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Kenis, M.; Hurley, B.P.; Colombari, F.; Lawson, S.; Sun, J.; Wilcken, C.; Weeks, R. and Sathyapala, S. 2019. Guide to the classical biological control of insect pests in planted and natural forests, FAO Forestry Paper No. 182. Rome, FAO.

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Cover photo: The sirex woodwasp, a serious pest of Pinus species. © B. HURLEY

Contents

Foreword

Acknowledgements

Acronyms

1Introduction

1.1 The threat to forests posed by insect pests

1.2 Managing insect pests

1.3 What is biological control?

1.4 Classical biological control

1.5 About this guide

2 Classical biological control

2.1 The benefits of classical biological control

2.2 Natural enemies used in classical biological control

2.3 Communication and classical biological control

2.4 The classical biological control process

3 Process leading to classical biological control

3.1 Pest detection

3.2 Pest identification and characterization

3.3 Pest risk analysis

3.4 Evaluating pest management options

3.5 Studying natural enemies in an invaded region

4 Implementing classical biological control

4.1 Reviewing potential biological control agents

4.2 Studying natural enemies in a pest’s native range

4.3 Importing biological control agents

4.4 Rearing and multiplying biological control agents in quarantine

4.5 Assessing the risk of introducing a biological control agent

4.6 Releasing biological control agents from quarantine

5 Monitoring and evaluating classical biological control

5.1 Post-release monitoring

5.2 Evaluating the success of a classical biological control programme

6 Other considerations

6.1 The Nagoya Protocol

6.2 Stakeholder engagement

6.3 The way forward

7 Case studies

7.1 Coconut rhinoceros beetle in the Pacific region

7.2 Great spruce bark beetle in Europe

7.3 Asian chestnut gall wasp in North America, northern Asia and Europe

7.4 Orthezia bug on Saint Helena

7.5 Eucalypt gall wasp

7.6 Bronze bug on Eucalyptus in Brazil

7.7 Mango mealybug in West Africa

7.8 Sirex woodwasp in Australasia, Africa, the Americas and Asia

7.9 Winter moth in Canada and the United States of America

7.10 Ambermarked birch leaf miner in Canada and the United States of America

7.11 Fall webworm in China

Glossary

Annex: List of pests, biological control agents and tree hosts mentioned in the guide

References and further reading

Figures

1 Stages, actions and decisions in a classical biological control programme

2 Floor plan for a basic physical containment/biosecurity level 2 quarantine facility

Boxes

1Categories of natural enemies used in classical biological control

2Studying natural enemies in an invaded region

3Classical biological control projects against the same insect pests in different countries

4Key considerations when transporting a biological control agent into an importing country

5Basic requirements for quarantine facilities for importing insect-pest biological control agents

6Physical containment/biosecurity levels for containing biological control agents securely

7Key considerations for receiving biological control agents into quarantine facilities

8Key biological characteristics to be understood when rearing an insect pest and its biological control agent

9Example of a parthenogenetic species used for classical biological control

10Criteria for selecting non-target test species

11Host-specificity study of native and non-native species as non-targets

12Assessing biological control agent effectiveness: parasitism rates

13Non-target effects of the biological control agent Compsilura concinnata

Foreword

Insect pests damage millions of hectares of forest worldwide each year. Moreover, the extent of such damage is increasing as international trade grows, facilitating the spread of insect pests, and as the impacts of climate change become more evident. Globally, and especially in developing economies, outbreaks of forest pests can have major consequences for the livelihoods of forest-dependent communities.

FAO views the threat posed by forest insect pests very seriously. Pest management is an important element of Sustainable Development Goal 15 (“Life on Land”), especially target 15.8: “By 2020, introduce measures to prevent the introduction and significantly reduce the impact of invasive alien species on land and water ecosystems and control or eradicate the priority species”. FAO’s ongoing programme on integrated pest management supports the achievement of this target, including through classical biological control.

Classical biological control is a well-tried, cost-effective approach to the management of invasive pest species. It involves the importing of “natural enemies” (parasitoids, predators and pathogens) of non-native pests from their countries of origin with the aim of establishing permanent, self-sustaining populations capable of reducing pest populations to below acceptable damage thresholds. Classical biological control is especially well suited as a management tool for exotic pests that invade new environments, and it can provide long-term, efcacious control at minimal ongoing cost. It also poses risks and it is crucial, therefore, that it is implemented with adequate safeguards.

A great deal of knowledge on classical biological control has been accumulated worldwide in the last few decades. This publication, which was written by a team of experts, distils that information in a clear, concise guide aimed at helping forest-health practitioners and forest managers – especially in developing countries – to implement successful classical biological control programmes. It provides general theory and practical guidelines, explains the “why” and “how” of classical biological control in forestry, and addresses the potential risks associated with such programmes. It features 11 case studies of successful efforts to implement classical biological control around the world.

I thank everyone involved in producing this document, especially the authors and all those who participated in the expert meetings that gave rise to the work. I have no doubt that the application of this guide in diverse situations will help in the safe, effective use of classical biological control and thereby in ensuring the health and productivity of the world’s forests.

Acknowledgements

Shiroma Sathyapala, FAO Forestry Officer (Forest Health and Protection), coordinated the preparation of this publication under the overall guidance of Eva Müller, Director of Forestry Policy and Resources, FAO Forestry Department. Two international expert meetings were convened to assist in preparing the publication, the first in Rome, Italy, in March 2017 and the second in Langkawi, Malaysia, in September 2017. FAO thanks Carl Rankin for facilitating both meetings as well as online consultations and for preparing a first draft of the document based on inputs received from experts. The following members of a peer-review group are acknowledged for their contributions and comments on various drafts of the publication: independent reviewers Professor Timothy D. Paine and Dr Eston Mutitu; Avetik Nersisyan and Sandra Goritschnig from the International Plant Protection Convention; Andrei Orlinski from the European and Mediterranean Plant Protection Organization; and Mette Løyche Wilkie from the FAO Forestry Department. FAO acknowledges the contributions made to the needs-assessment survey by members of the Asia-Pacic Forest Invasive Species Network, the Forest Invasive Species Network for Europe and Central Asia, the Near East Forest Health and Invasive Species Network, the Forest Invasive Species Network for Africa, and Federica Urbani at FAO. Many thanks to technical editor Susan House, copyeditor Alastair Sarre and designer Kate Ferrucci for their contributions.

FAO also thanks the authors of this guide: Dr Marc Kenis, Centre for Agriculture and Biosciences International, Switzerland; Dr Brett Hurley, Forestry and Agricultural Biotechnology Institute, University of Pretoria, South Africa; Dr Fernanda Colombari, University of Padova, Italy; Dr Simon Lawson, University of the Sunshine Coast, Australia; Professor Carlos Wilcken, São Paulo State University, Brazil; Dr Jianghua Sun, Institute of Zoology, Chinese Academy of Sciences, China; Dr Ronald D. Weeks, United States Department of Agriculture, United States of America; and Dr Shiroma Sathyapala, FAO, Rome.

Acronyms

BCAbiological control agent

BSbiosecurity

CBCclassical biological control

CBDConvention on Biological Diversity

FAOFood and Agriculture Organization of the United Nations

IOBC International Organisation for Biological and Integrated Control

IPMintegrated pest management

IPPCInternational Plant Protection Convention

ISPMInternational Standard for Phytosanitary Measures

NPPOnational plant protection organization

PCphysical containment

PRApest risk analysis

WHOWorld Health Organization

Introduction

1.1 The threat to forests posed by insect pests

Planted and natural forests provide many economic, social and environmental benefits. For example, they help combat desertification, protect watersheds, regulate climate, conserve biodiversity and maintain social and cultural values. In economically developing countries, forests help meet basic needs for food, medicines, timber, energy and fodder.

Insect pest outbreaks damage about 35 million hectares of forests annually, mainly in the temperate and boreal zones (FAO, 2010). Such outbreaks are increasing globally as the volume and speed of international trade escalates and the climate changes.

In planted and natural forests, endemic insects and tree diseases are integral components of ecosystems. The introduction of non-native insect pests to new areas where they have no natural enemies, however, can have catastrophic impacts. Damage caused by invasive forest insect pests can reduce tree growth and timber quality and production, cause declines in biodiversity, significantly affect vital forest ecosystem functions and change entire landscapes. Although native forest pests can have similar effects, usually these are more sporadic and can be managed by modifications to management regimes.

In economically developing countries, non-native forest insect pests can cause severe economic losses, affecting the livelihoods and food security of many forest-dependent people. It is crucial, therefore, to manage insect pests appropriately. Pest management is an important element of Sustainable Development Goal 15 (“Life on Land”), especially target 15.8: “By 2020, introduce measures to prevent the introduction and significantly reduce the impact of invasive alien species on land and water ecosystems and control or eradicate the priority species”.

1.2 Managing insect pests

Forest insect pests can be managed by the deployment of resistant or tolerant germplasm and by chemical, cultural and biological means. These various methods can be applied compatibly as part of integrated pest management (IPM) – a widely accepted approach implemented in both natural and planted forests worldwide (see section 3.4).

1.3 What is biological control?

Biological control involves the use of “natural enemies” as an essential component of IPM. In a broad sense, a natural enemy is an organism that causes the death or impairment of another organism. Biological control can be defined as using living natural enemies (“beneficial organisms”) to control other living organisms (“pests”). International Standard for Phytosanitary Measures (ISPM) 3 defines a biological control agent (BCA) as a “natural enemy, antagonist or competitor, or other organism, used for pest control”. The objective of all biological control programmes in forestry and agriculture is to reduce the impacts of pests to below acceptable thresholds. Biological control can be used alone or in combination with other control methods in IPM programmes.

There are three main approaches to biological control:

1. Augmentation biological control – increasing the density of native or non-native natural enemies with regular releases. Releases may be made

- at the beginning of each season, when relatively few individuals of a natural enemy are released (these are expected to reproduce during a certain period), or

- as a single mass release of a natural enemy expected to result in immediate control.

2. Conservation biological control – the manipulation of habitat with the aim of enhancing the reproduction, survival and efficacy of natural enemies already present in an affected area.

3. Classical biological control (CBC) – the introduction of a natural enemy of non-native origin to control a pest, usually also non-native, with the aim of establishing a population of the natural enemy sufficient to achieve the sustainable control of the target pest.

1.4 Classical biological control

CBC is often a key component of IPM in forestry. It consists of controlling non-native pests by importing natural enemies (parasitoids, predators or pathogens) from their countries of origin. The objective is to establish permanent, self-sustaining populations of natural enemies that will disperse and suppress a pest population or reduce its rate of spread, including as part of wider IPM systems. Although, on its own, a CBC programme will not eradicate an invasive pest species, it can help reduce the population to below an acceptable threshold of damage. CBC is particularly well-suited as a management tool for non-native pests that invade new environments and can provide long-term, efficacious control at minimal ongoing cost.

1.5 About this guide

This guide has been written to enable forest-related personnel in economically developing countries to implement successful CBC programmes. It provides general theory and practical guidelines, explains the “why” (background and understanding) and “how” of forest pest control using CBC, and features 11 case studies of the successful application of CBC worldwide. CBC can be used to target many kinds of organism, including invasive plants and pathogens. This guide is concerned with forest insect pests, although its recommendations may also be valid for agricultural ecosystems.

Chapter 2 provides an introduction to some of the basic elements of a CBC programme. Chapters 3–5 examine the three main stages of a CBC programme, focusing especially on aspects of planning, implementation and the monitoring and evaluation of outcomes. Chapter 6 canvasses other important considerations, and Chapter 7 presents case studies. A glossary provides definitions of many of the technical terms used in this guide, and an annex lists the main species and genera of pests, BCAs and tree hosts described herein.

This guide is designed to complement a key FAO Forestry Paper, Guide to the Implementation of Phytosanitary Standards in Forestry (FAO, 2011), and the International Standards for Phytosanitary Measures, especially ISPM 3: Guidelines for the Export, Shipment, Import and Release of Biological Control Agents and Other Beneficial Organisms. Both these documents, which are available free of charge, should be consulted in tandem with this guide.

2 Classical biological control

2.1 The benefits of classical biological control

CBC is a permanent, self-sustaining form of pest control. These qualities give CBC an important advantage over chemical and silvicultural pest-control methods as well as over the augmentation and conservation biological control methods. Once established, non-native natural enemies of targeted pests should require no further intervention, thus potentially resulting in substantial cost savings and economic benefits. For example, the CBC project against the mango mealybug in Africa generated an estimated cost–benefit ratio of 1:808 over 40 years (case study 7.7).[1]

Successful CBC projects enable reductions in the use of insecticides, which has substantial benefits for human health and the environment. CBC programmes are increasingly being developed to protect biodiversity and natural ecosystems where the use of pesticides is not an option – such as in the case of the orthezia bug on the island of Saint Helena (case study 7.4). CBC is also being used in protected areas – such as the Galapagos Islands, where the vedalia beetle (Rodolia cardinalis) has been introduced to help manage the impact of cottony cushion scale (Icerya purchasi), a plant pest.

2.2 Natural enemies used in classical biological control

In CBC, one or more of a pest’s natural enemies are selected as potential BCAs. They may be parasitoids, predators or pathogens (Box 1), and they are most often sourced from a pest’s native range, although related taxa from other invaded regions or elsewhere may also be considered.

2.3 Communication and classical biological control

All CBC programmes should include awareness campaigns aimed at the programme’s main beneficiaries (e.g. farmers, foresters and consumers). The objectives of such campaigns should be clear – such as to inform stakeholders about the intention to implement CBC and to provide updates on the process. It is important to initiate awareness campaigns very early on – as soon as the decision has been made to use CBC. Awareness campaigns must be maintained throughout the duration of a CBC programme using appropriate media to reach all affected stakeholders, including the public.

2.4 The classical biological control process

CBC programmes have two main phases (Figure 1):

1. the process to develop a CBC programme (described in Chapter 3); and

2. the implementation of a CBC programme (described in Chapter 4; see also Chapter 5 on monitoring and evaluation, which are parts of implementation).

3 Process leading to classical biological control

3.1 Pest detection

Globally, a range of phytosanitary measures is employed to limit the risk of accidental introductions of new invasive alien pests. One approach to managing high-risk pathways for such introductions is to implement ISPM 15: Regulation of Wood Packaging Material in International Trade, which is a phytosanitary standard designed to minimize the movement of pests in wood packaging. The FAO publication, Guide to the Implementation of Phytosanitary Standards in Forestry (FAO, 2011), outlines the most applicable phytosanitary practices in forestry.

Despite such measures, however, the potential remains for the introduction of invasive alien pests into countries and regions where they have not occurred previously. Such introductions, when detected, are the usual targets of CBC programmes.

Surveillance

Pests may be detected using active or passive surveillance. Active surveillance comprises structured, systematic and targeted surveys of trees and forests by trained personnel. Passive surveillance relies on reports of unusual signs, symptoms or pest insects on trees or in forests by stakeholders such as farmers and forest workers. Surveillance should target three main locations:

1. borders;

2. post-border areas; and

3. plantations, natural forests and urban forests.

Borders. Border surveillance involves inspecting goods arriving in a country for signs of pests (or the symptoms of these). Due to the large volumes involved, only a small proportion of such goods can be inspected. Even so, interception records are valuable indicators of which pests are moving around the world, the frequency at which they are moving and the pathways they are using. This knowledge helps improve pre-border phytosanitary measures, import protocols and post-border surveillance.

Post-border areas. Targeted surveillance can be carried out at high-risk sites (e.g. seaports, airports, import warehouses, container and pallet depots, and botanic gardens) using, for example:

•insect traps (e.g. those using pheromones or other lures, sticky traps, and light traps);

•sentinel plants (i.e. plants cultivated and located to attract known or new pests or diseases); and

•intensive (“blitz”) surveys of insects and pathogens on trees and other woody plants along transects at high-risk entry sites.

Plantations, natural forests and urban forests. In many forests, surveillance is carried out as a routine part of management to assess forest health and to detect outbreaks of endemic or new pests. Methods include:

•walk-through surveys (along transects);

•drive-through surveys;

•aerial surveys (fixed-wing aircraft, helicopters and, increasingly, unmanned aerial vehicles – drones); and

•remote sensing (from aircraft or satellites).

ISPM 6: Surveillance describes general surveillance and specific surveys and stipulates the necessary components of surveys and monitoring systems for the purposes of plant-pest detection.

Actions following detection

Reporting. If a suspected new exotic pest is detected, an essential first action is to report this to the relevant national or provincial plant protection or biosecurity agency. ISPM 17: Pest Reporting describes how this should be done. Such reporting will trigger official responses and notifications.

Response plans. A regulatory framework that includes preparedness and response plans for pest incursions is highly desirable. Response plans can be generic or pest-specific: Australia’s “PLANTPLAN” response plan developed by government and industry (Plant Health Australia, 2017) is an example of good practice for a generic approach.

Early responses under a response plan typically include:

•delimiting the surveillance area to determine the distribution of the pest;

•convening an expert panel to make early management decisions based on knowledge of the biology, ecology and economic importance of the pest, public awareness and contingency plans; and

•restricting the movement of potentially pest-infested goods to prevent the pest’s spread.

The next step is to decide whether eradication is feasible or if another option, such as containment to limit the spread of the pest, is more appropriate. The earlier a pest is detected, the higher the probability of eradicating it, containing it or limiting its spread.

3.2 Pest identification and characterization

Identification

As soon as a potential insect pest is detected, it is important to identify it correctly to determine whether it is:

•new to the country or region;

•a native species; or

•an already-established non-native species.

This means it is essential to know which insects are present locally. Such information might be obtained from local historical records of pest occurrence; scientific literature; previous surveys of forest pests; and the local knowledge of forest growers and tree owners.

Images and specimens of potential new pests can be directed to local taxonomic experts, if available, for rapid identification, and they can also be sent to international experts. Resources required for local identification include:

•access to good-quality microscopes (ideally fitted with cameras for taking high-quality images); and

•taxonomic keys relevant to the insect involved.

Many online resources are available to assist with provisional pest identification, including Internet image searches (e.g. Forestry Images, PaDIL and online insect identification keys);[2] email discussion groups such as PestNet;[3] and software applications (“apps”) for mobile devices.

If experienced morphological taxonomists are unavailable to make authoritative diagnoses, molecular barcoding is the next best option for identification. This requires access to a molecular-biology laboratory and experienced staff to carry out analyses and interpret results. If such facilities and personnel are unavailable in-country, appropriately preserved specimens can be sent internationally for analysis as per national protocols. An advantage of molecular-based diagnoses is that they may also be able to identify a pest’s region of origin, which could be important for a biological control programme.

Characterization

Characterizing a new pest means documenting its biology, ecology and known management options. Early characterization can be obtained by reviewing the scientific literature, which could contain detailed relevant information if the insect is a known pest. If the insect is not well known, scientific literature might exist for closely related species that share similar biological traits.

Crucial information needed for assessing risk and management options includes:

•Host range

•Life-cycle duration

•Global distribution

•Climatic requirements

•Dispersal ability

•Control methods

•Nature of damage or symptoms on host

•Associated natural enemies.

3.3 Pest risk analysis

When a new insect is detected, a pest risk analysis (PRA) is conducted to:

•determine whether the organism is a pest and is likely to establish and spread in the country;

•evaluate whether and to what extent the pest has the potential to cause economic, social and environmental damage;

•evaluate the potential impacts on international trade; and

•determine any phytosanitary measures to be taken against it.

A PRA will provide sufficient information to determine whether the newly detected insect is a significant pest that should be managed. It is important, therefore, to determine the risk posed by an insect as soon as possible after it is detected. ISPM 2: Framework for Pest Risk Analysis, ISPM 11: Pest Risk Analysis for Quarantine Pests, and ISPM 21: Pest Risk Analysis for Regulated Non Quarantine Pests describe the processes for PRA and for selecting appropriate risk management options, and they provide information on assessing plant-pest risks to the environment and biodiversity. Some regional plant-protection organizations (e.g. the European and Mediterranean Plant Protection Organization) and countries (e.g. Australia and New Zealand) have specific PRA processes. A country’s national plant protection organization (NPPO) or delegated authority should conduct PRAs for newly found non-native insects.

A PRA requires an understanding of the ecology and behaviour of the insect, including the range of suitable hosts and its life stages, method and rate of reproduction, life-cycle duration and climatic requirements. PRAs consider the potential impacts of pest damage on forest plantations, including losses in nursery production, total crop losses, reduced growth rates, poor tree form and decreased wood quality. In native forest ecosystems, negative impacts on tree species may cause changes in forest composition and a consequent loss of habitat for wildlife dependent on affected tree species.

Where possible and practicable, estimates should be made of production losses. These are relatively easy to make when damage is severe (e.g. the total loss of a plantation) and more difficult if damage has subtler effects on growth rates and wood quality. Where the impact is on growth rates, impact assessments may be needed over several years because growth losses may take some time to be realized and many tree species have significant capacity to compensate for defoliation.

The scientific literature and historical records of pests detected in other countries or regions may provide much of the information needed for conducting a PRA. It is especially important to obtain information from other invaded areas because the actions of natural enemies may suppress an insect pest in its native range.

Key considerations that can help initiate a PRA include the following:

•Is the insect invasive in other countries?

•Is the insect a significant pest in other countries or regions or in its native range?

•Is the insect included in national and international pest lists?

•Have previous PRAs been conducted in other countries?

•Which tree host(s) has the insect affected?

•How severe is the damage and does this vary according to host species?

•What is the insect’s current distribution?

•Is the distribution or range increasing?

•Are response plans available in other countries?

•What methods are used to control the insect in other countries?

3.4 Evaluating pest management options

If a PRA concludes that the risk is high enough to take action, options such as eradication, containment and management should be evaluated to determine which is most appropriate. Note that a combination of several management methods can be used in an IPM approach.

Eradication

The eradication of a new pest may be feasible if surveys show it has a limited distribution. Other aspects to consider are the pest’s dispersal and reproductive ability and the availability of control methods with a high probability of eliminating the pest. Such methods may include:

•effective chemical and biopesticide treatments;

•traps that can be baited with pheromones or kairomones (see “semiochemicals” below) that efficiently trap the pest and reduce numbers quickly; and

•especially for bark- and wood-boring pests, the removal and destruction of infested trees.

More information on pest-eradication strategies is available in ISPM 9: Guidelines for Pest Eradication Programmes.

Containment

If a pest is not eradicable or eradication fails, containing the pest may be the next-best option. The objective of containment is to prevent the pest from expanding its range or at least to slow its spread to other areas. Methods usually focus on limiting human-assisted spread, for example by restricting the movement of nursery material and timber products. Methods for eradicating a pest can also be used for its containment.

If a pest cannot be eradicated or contained, other management methods should be evaluated.

Integrated pest management

IPM is the combination of prevention, monitoring and suppression methods to sustainably maintain pest populations at an economically, socially and environmentally acceptable level. IPM may involve carefully selected and applied chemical, silvicultural and biological control practices.

For IPM to be effective, field practitioners need a reasonable knowledge of the biology and ecology of the pests and host trees involved. They also need a good understanding of the control methods used in forestry, as described below.

Chemical control

Insecticides are commonly used worldwide as a control method in forestry. Increasingly, however, chemical use is being restricted due to its negative impacts on the environment and human health. Forest sustainability certification schemes, such as that of the Forest Stewardship Council, impose strict conditions and restrictions on chemical use by forest managers seeking certification for their products. “Soft” insecticides (those with few off-target impacts) can still form an important part of IPM systems when used appropriately. Evaluations should determine:

•which chemicals may be effective against the new pest;

•whether those chemicals are registered for use in forestry; and

•whether the use of such chemicals is permitted under the Forest Stewardship Council and other certification schemes.

Emergency-use registrations can sometimes be obtained for eradication programmes. The Joint FAO/World Health Organization (WHO) Meeting on Pesticide Residues and the Joint FAO/WHO Meeting on Pesticide Specifications have generated a list of evaluated pesticides.[4]

Silvicultural control

Some pests can be managed effectively by altering silvicultural practices; this requires a good understanding of interactions between a pest’s biology and silvicultural practices. Changes in silvicultural practices may include removing trees that are current or imminent sources of infestation and altering the timing of planting, thinning, pruning or harvesting. Interactions between soil nutrition and the application of fertilizers may also be important. Decisions on silvicultural pest-control practices require close collaboration between entomologists and silviculturalists, who should jointly determine which manipulations are likely to be effective and whether implementation is practical.

Tree resistance or tolerance

Any resistance to or tolerance of a new pest among tree hosts should be identified as early as possible. Selecting for genetic resistance in tree populations, and subsequently growing resistant varieties, can be an effective method for managing new pests. On the other hand, the developers of resistant germplasm often retain ownership rights to this genetic material, which therefore may not be readily available to small-scale growers, at least in the short term.

The time it takes to identify resistance to or tolerance of a new pest, develop the germplasm and deploy the plants will depend, to some extent, on the age at which trees become susceptible. For example, resistance to a pest that attacks seedlings can be screened for and deployed much faster than resistance to a borer pest that attacks older trees. Genetic markers of resistance or tolerance can be used to speed this process, but this will require significant investment in research.

Semiochemicals

The methods insects use to find mates and locate hosts can be exploited in management programmes. Pheromones (insect-produced chemicals that affect the behaviour of individuals of the same species) and kairomones (chemicals produced by one species that influence the behaviours of other species) are used widely to manage pests. Pheromones, which are species-specific, are an especially useful tool for monitoring insect populations and reducing population numbers. Suitable chemicals may already be available for certain well-known pests but, for new pests, discovering, testing and commercializing behavioural semiochemicals can be a long and expensive process.

Literature searches and expert advice will ascertain whether potentially effective semiochemicals are available for monitoring and regulating populations of a new pest (e.g. Pherobase is a good resource for semiochemical information).[5] Effective semiochemicals (as well as suitable traps and methods for applying the chemicals) are available for some common invasive forest pests, with several companies specializing in such products.

Biological control

Biological control – the use of natural enemies to regulate pest populations – is a frequently employed and often-effective management practice. There are three main approaches, which mostly apply either to already-existing endemic or exotic pests or to newly introduced non-native pests:

1. Conservation biological control

2. Augmentation biological control

3. Classical biological control.

Conservation biological control. Cultural practices that conserve existing thriving natural enemies in an ecosystem by providing them with suitable conditions include, for example:

•encouraging nectar sources for parasitoids to enhance their survival and reproductive capacity;

•providing habitats in which natural enemies can survive during unfavourable conditions (e.g. after a crop has been harvested), such as by promoting the growth of plant hosts that help maintain natural-enemy populations; and

•reducing the effect that pesticides have on natural enemies, for example by switching to biopesticides or reducing pesticide dosages.

Augmentation biological control. This approach involves continually rearing, multiplying and releasing natural enemies of a pest – generally in large numbers at the same location repeatedly. Augmentation biological control is usually used when natural control systems are ineffective and other methods (e.g. the use of chemicals) are undesirable. Natural enemies used in augmentation biological control are often supplied commercially by specialized businesses. This approach also includes the use of entomopathogens as biopesticides.

Classical biological control. CBC involves importing natural enemies from a pest’s endemic range and releasing them to become established in the new country or region as a means of providing ongoing pest control. This method is the focus of this guide.

3.5 Studying natural enemies in an invaded region

In evaluating the options for IPM, early surveys of a pest will have determined whether natural enemies are already present and having a significant impact on the pest population. Such natural enemies may be from the endemic range of the pest that have travelled with it, or they may be organisms endemic to the invaded region that are exploiting the new pest as a host or prey (Box 2).

Knowing whether an existing natural enemy is effective will have an impact on decisions to import BCAs as part of a CBC programme. The presence of local natural enemies of a new pest also opens up opportunities for conservation and augmentation biological control.

4 Implementing classical biological control

When CBC is selected as the biological control method, the next step is to determine a suitable BCA, which must meet import and quarantine regulations before it can be reared and released.

4.1 Reviewing potential biological control agents

Any CBC programme should be based on a thorough understanding of similar previous programmes against the target pest and of the natural enemies that could be used as BCAs.

Review previous and existing biological control programmes

A comprehensive literature review should be carried out on previous and existing biological control programmes for the target pest and any known natural enemies of the pest in other parts of the world. Given that pests often invade more than one area, several CBC programmes for a target pest may already exist (Box 3). Much can be learned from these, but bear in mind that the same pest may need different control measures in different areas. Nevertheless, obtaining as much information as possible from previous and existing CBC programmes and potential BCAs will undoubtedly help in planning the new CBC programme and in minimizing costs.

The literature review should cover all the information available on CBC against the target pest, including primary publications and reports, and it should consult CBC project databases worldwide. Every piece of information that may be relevant to the planned CBC programme should be examined, including natural-enemy complexes in various regions, natural-enemy selection processes and rearing and release methods, and programme outcomes. The strengths, weaknesses and challenges of previous programmes should be assessed.

If no information exists on previous CBC projects carried out against a target pest, published information on the target pest’s natural enemies should be reviewed. This will assist surveys for natural enemies in the native range, and investigations may also provide opportunities for collaborating with experts in CBC against the pest and obtaining access to supplies of BCAs. Collaboration might also be possible with experts in the native range, who could provide support for surveys and expertise in other relevant areas.

Preliminary investigations may lead to one of the following three main findings:

1. Previously successful CBC programmes exist – when a previous CBC programme has been successful, the option of introducing the same natural enemy through the planned programme may be considered if:

- the environmental conditions in the previous programme were similar to the conditions of the planned CBC programme (e.g. similar climate and habitats); and

- analysis of the previous programme suggests that the most suitable natural enemy was chosen.

In this case, surveys and studies in the native range (see section 4.2) may be unnecessary. Nevertheless, the potential for non-target effects should be considered because biodiversity in the planned area of introduction may differ from that in the previous CBC programme.

2. Previous studies concluded that no suitable natural enemies exist – if comprehensive surveys and studies to find a BCA conclude that no suitable natural enemy exists in the native range, discontinuing the planned CBC programme should be considered.

3. More information is needed about natural enemies as potential BCAs – in all other cases (for example, CBC has not previously been carried out against the pest, previous CBC programmes were poorly executed, or the environment in the new target area differs significantly from those previously targeted) the planned CBC programme should continue with surveys of natural enemies in the native range.

4.2 Studying natural enemies in a pest’s native range

Purpose

Understanding the natural-enemy complex of a target pest in its native range (and especially the respective roles of natural enemies in controlling pest populations) will help in selecting the most efficient and safe BCAs to introduce to the infested area. This knowledge may already be available for some target pests, for example from previous CBC programmes in other parts of the world. If the natural-enemy complex is not well known, however, a study is a key requirement. It may also be the most time-consuming and expensive step in the entire CBC programme.

Collaborate closely with local agencies

Studying the natural-enemy complex in its native range must always be done in close collaboration with relevant national institutions, such as universities, research institutes and government agencies. These institutions can provide logistical support and scientific collaboration, and they can share the knowledge generated, for example through joint publications and the sharing of voucher specimens. All studies in the native range should adhere to the laws of the surveyed countries, especially in relation to the sampling and exporting of insects and plant materials. The NPPO of the country of survey should be the first point of contact for information on exporting insects, other natural enemies and plant materials.

Survey a relevant sample of the pest’s native range

Because a pest’s native range is often large and not clearly defined, it is usually not possible to survey its entirety. The main survey areas for a natural-enemy complex should be selected using the following two criteria:

1. Survey areas similar to the area of introduction – surveys should concentrate on areas that are climatically and ecologically most similar to the intended range of introduction (or the target area, if the CBC programme will focus on only a part of the introduction range). Computer programmes such as CLIMEX can be used to help determine similarities in climatic conditions (“matching”) and the likely effects on species in the area where the natural enemy is to be introduced.

2. Survey the pest’s area of origin – where possible, surveys should focus on the putative (presumed) point of origin of a pest. The true “native range” is difficult to define, however, because the pest may have invaded areas many years previously, and this “naturalized range” may be difficult to distinguish from its native range; this is particularly the case where host trees have been planted outside their native ranges. For example, the boxwood tree moth (Cydalima perspectalis), an invasive species in Europe and the Caucasus, is thought to be native to China, where it occurs on ornamental boxwood trees (Buxus spp.) in most provinces. Because natural stands of boxwood trees occur in only a limited area, however, other Chinese provinces are considered to be invaded areas and only part of the original natural-enemy complex may be present there. In this case, surveys of natural enemies should be conducted in natural stands of boxwood or in ornamental boxwood trees in the same areas.

In some cases, a pest’s area of origin can be determined through genetic studies using molecular tools. If the area of origin remains unknown, however, surveys of natural enemies should focus on the most likely areas of origin, especially those that are climatically and ecologically similar to the target area of the CBC programme.

Objectives of natural-enemy studies in pest’s native range

Survey natural enemies in the field and quantify their impacts on the pest. All life stages of a pest should be collected in the field and reared in the laboratory so that naturally occurring parasitoids and pathogens might be found. Methods will differ, depending on the target insect pest and its developmental stages; researchers should be encouraged, therefore, to consult the scientific literature related to the relevant insect group and its natural enemies.

Parasitoids are often the easiest natural enemies to obtain and quantify (compared with predators and pathogens) because they can be reared from material collected in the field. Apparent rates of parasitism can be measured by dividing the number of emerged parasitoids by the sum of the number of hosts and parasitoids. Note that there is potential for error in this method. The results will be influenced by the timing of collection of the parasitized hosts, which is related to:

•the time during which the hosts were available to be parasitized; and

•the proportion of hosts and parasitoids that would have already emerged.

This error can be reduced by repeated sampling at different times.

Pathogens of insect pests can also be identified through field collections. Quantifying the mortality caused by such pathogens is unreliable if based solely on field collections, however, because excessive mortality may occur in laboratory rearing. Some pathogens do not kill their host insects directly but reduce measures of fitness such as longevity and fecundity. Such factors can only be assessed in specific laboratory studies, which are rarely part of CBC programmes (on the other hand, programmes for the sirex woodwasp routinely assess the influence of the entomopathogenic nematode BCA, Deladenus siricidicola, on the woodwasp’s fertility – see case study 7.8).

Predators are the most difficult natural enemies to study because they rarely leave signs of attack when they eat or kill their prey. Identifying predators requires careful observation, sampling in the field, and further testing in the laboratory. Quantifying the effects of predators on target pest populations is even more challenging.

What level of detail is required to study the effects of natural enemies? Quantifying the exact effects of natural enemies on pest mortality can be done using the life-table method. In this approach, all developmental stages are studied separately in field conditions and the various mortality factors are quantified for each stage. Life tables are useful for comparing the effects of mortality factors in the native and introduction ranges, but their use is very time-consuming and their efficiency varies by insect group. For these reasons, life-table studies are rarely carried out in CBC programmes. Note that it is usually unnecessary to gather accurate data on the mortality caused by natural enemies in the native range because mortality rates tend to vary substantially between the native and introduction ranges. Thus, identifying apparently important natural enemies in the native range is usually sufficient for their further evaluation.

Study the biology and ecology of pests and natural enemies in their native ranges. The successful introduction of a BCA requires in-depth knowledge of the biology and ecology of the pest and its natural enemies. This knowledge is gained through a combination of literature reviews and field and laboratory research. Biological and ecological studies of pests and natural enemies will be more relevant and valid if done in the field or in non-quarantine laboratory conditions in the native range rather than in the constrained conditions of a quarantine laboratory in the introduced range. Knowing the biological and ecological characteristics of natural enemies helps in assessing whether a parasitoid, predator or pathogen will adapt to the pest and environment in the introduction area. The availability of this information will also greatly simplify studies conducted in quarantine conditions in the introduction area or elsewhere.

Selecting which studies to conduct will depend on what is known about the pest and its natural enemies and how easy it is to do field work in the native range. Potential aspects for study include the following:

•Life cycle of pest’s natural enemies and other potential hosts or prey – this type of study may help determine the specific stage(s) at which a natural enemy attacks or kills a pest host or prey. It may also identify the natural enemy’s fecundity, pest resistance, pre-oviposition period, development time, host-stage suitability and preference, and intraspecific competition, as well as any potential non-target effects.

•Climatic requirements of natural enemies – climatic requirements are assessed through field surveys in climatically different areas and also in laboratory studies of a natural enemy’s development under differing temperatures and humidities and its cold and heat hardiness. In some CBC programmes, studies of climatic requirements generate climate models for predicting establishment success for a natural enemy in the introduction area. Climatic requirements can also be modelled or predicted from location data in previous collections, including data from museum specimens.

•Habitat preferences of natural enemies – field surveys can determine a natural enemy’s habitat preferences at the scale of both macrohabitat (e.g. humid versus dry zones) and microhabitat (e.g. preferred host plant species for parasitism).

•Associated cryptic species and biotypes – it is now clear that many pests and their natural enemies once thought to belong to single species actually comprise several cryptic species or biotypes of the same species. Such species or biotypes may differ in important traits such as host range, host preference, climatic requirements and fecundity. Thus, it is essential to select the most appropriate species and biotypes for further testing and potential introduction. Characterizing cryptic species and biotypes can begin in the native (indigenous) range using three interdependent selection approaches based on collections of several populations from different regions, hosts or habitats:

1. Test the different populations of species or biotypes for traits such as climatic requirements and host specificity (or preference) in the laboratory.

2. Sequence the different populations using molecular approaches (barcoding) to detect different lineages.

3. If cryptic species are suspected, perform crossings to assess their reproductive compatibility.

•Elements of population dynamics – a natural enemy’s potential to control a pest at various pest densities can be assessed by determining the host–parasitoid, host–pathogen or prey–predator density dependencies.

Studies on rearing natural enemies and host-specificity assessments are usually conducted in quarantine facilities in the introduction area (see sections 4.4 and 4.5). It is also possible, however, to gather important information on these aspects in the native ranges.

4.3 Importing biological control agents

This section describes the process for importing BCAs to manage forest insect pests, as set out in ISPM 3: Guidelines for the Export, Shipment, Import and Release of Biological Control Agents and Other Beneficial Organisms. ISPM 3 lists the principles for facilitating safe trade and using BCAs and describes the responsibilities of an exporting country’s NPPO, the exporter and importer, and the importing country’s NPPO before, during and after importing a BCA.

Import and export requirements for biological control agents

Before importing or exporting a BCA, both the importer and exporter should contact their respective NPPOs or other relevant authorities to ensure they understand the specific requirements for moving the BCA safely from one country to another.

Import requirements. In most countries, the importing process cannot begin until an import permit or licence has been issued to the importer. A permit or licence is the official authorizing document that describes the import requirements, as developed by the importing country’s NPPO based on the results of a risk assessment. If the risk of importing a BCA can be managed adequately, the importing country’s NPPO will issue the permit or licence to allow the BCA to be brought in, provided that the consignment meets the specified requirements. Some countries may require evidence of a risk assessment and cost–benefit analysis before granting a permit to import a BCA into containment.

Export consignment requirements. A BCA consignment for export is prepared according to the import requirements of the import permit or licence and any other regulatory conditions. In some countries, exporters may need to obtain export permits issued by the relevant agency in the exporting country before exporting BCAs. The relevant agency in the exporting country will need to be satisfied that a consignment meets all requirements before issuing the relevant certification, such as a phytosanitary certificate or an export permit.

Transporting biological control agents

Transporting a BCA between countries can be very challenging given differing rules and regulations of the importing and exporting countries (and, potentially, of transit countries). It is crucial to check with all countries involved before attempting to transport a BCA (Box 4).

Requirements for quarantine facilities at import destination

Quarantine facilities are used to ensure that imported BCAs are reared and studied in containment before permission is granted for their release.

There is no internationally agreed standard for establishing and maintaining quarantine facilities for rearing and multiplying BCAs. The European and Mediterranean Plant Protection Organization, the North American Plant Protection Organization, and countries such as Australia, Canada, Japan, New Zealand, the Republic of Korea and the United Kingdom of Great Britain and Northern Ireland have their own standards. Because legal requirements for the establishment, maintenance and use of quarantine facilities can differ between countries, it is essential to work closely with relevant NPPOs or other delegated authorities. In all cases, the relevant NPPO or other delegated authority is accountable for the initial approval and ongoing audits of quarantine facilities. Quarantine facilities must have the necessary approvals in place before receiving BCAs. Box 5 sets out basic good-practice requirements and considerations for quarantine facilities containing insect BCAs.

Quarantine facilities should be designed to accommodate containment rooms with special ventilation that can manage a wide temperature range, elevated relative humidity, and potential allergy problems related to insect-rearing. Some quarantine facilities also have separate greenhouses to provide adequate natural and artificial light for normal plant growth and insect behaviour.

Quarantine facilities are required to meet standard levels of physical containment (PC) depending on the nature of the BCA and the risk associated with it. Some countries specify the same PC levels as those used for biosecurity (BS). There are four generally accepted PC/BS levels reflecting the status of a quarantine facility and the systems in place to contain BCAs safely. PC/BS levels 1–3 apply mainly to quarantine facilities handling BCAs, and PC/BS level 4 is typically used for dangerous arthropods with implications for human health. Box 6 summarizes PC/BS levels 1–3 for quarantine facilities.

Establishing and maintaining quarantine facilities requires ongoing resources (the higher the PC/BS level, the more resources required). Where feasible, countries or regions should consider sharing facilities.

In the basic PC/BS level 2 quarantine facility depicted in Figure 2, entry and exit are via darkened airlocks 1 and 2 only. Note that all doors open inwards, creating a small negative pressure when opened. The workroom contains an autoclave, which must be used to process all material before it is disposed of outside. The “clean room” is where consignments of BCAs are opened and processed before the BCAs are moved into the laboratory for breeding and testing.

Receiving biological control agents into quarantine

Consignments of imported BCAs, whether couriered or hand-delivered, must go directly to an approved quarantine facility before they are opened.

Once received into the quarantine facility, a BCA consignment can be opened and the BCAs removed. The survival and condition of BCA specimens should be recorded, including the total number received, the percentage survival, the sex ratio, and comments on the apparent health of the specimens.

The contents of consignments should be assessed for contaminants – that is, other organisms that have been accidentally imported with a BCA, such as insects, hyperparasitoids, phoretic mites, nematodes and microbial pathogens of the BCA. This step is crucial: the introduction of contaminants into the release area could compromise the efficacy of the BCA (for example if the contaminants are hyperparasitoids or microbial pathogens of the BCA) or result in the accidental introduction of other pest species. Detected contaminants should be killed, identified and preserved as voucher specimens for future reference.

After all individuals of a BCA have been removed and the package examined for contaminants, all packing material should be destroyed according to quarantine operating procedures.

The identity of an imported BCA must be confirmed, where possible in consultation with appropriate taxonomic experts. It is good practice to use the BCA’s molecular barcode sequence in combination with taxonomic expertise to confirm a consignment’s identity, although this will only be possible if the species’ barcode sequence is available. In some cases, taxonomic expertise may be unavailable, and barcode sequencing may be the only method of species confirmation. Box 7 lists key considerations when receiving BCAs into quarantine.

The country’s NPPO and other relevant authorities must be notified of receipt of a BCA consignment, along with confirmation of the species’ identity and whether any contaminants were detected.

Receiving biological control agents for direct release

In some situations, an importing country may initiate a CBC programme without having its own in-country quarantine facility for rearing BCAs. In this case, it may be possible to import (and release) BCAs directly from participating laboratories or quarantine facilities in another country. To do so, it is crucial that the necessary permits, as well as research on rearing, environmental impacts (including non-target assessments) and releases conducted by the participating laboratories, are completed – in accordance with the requirements of the importing country – before the dispatch of a BCA to the importing country. Although this is not the ideal way to import a non-native BCA into a new environment, it can be done safely through carefully coordinated partnerships.

Transporting a live BCA requires packaging that prevents specimens of the BCA from escaping and maintains the consignment’s viability. Where possible, a small test shipment of the BCA should be conducted to test the importation process. Arrangements should be made with relevant authorities to clear shipments promptly at the point of entry (e.g. an international airport). Consignments should be transferred to a suitable facility with minimal delay and placed in cages or screened greenhouses to be opened, sorted and studied.

Before a BCA is imported, the exporter should take the utmost care to ensure that consignments will not be contaminated (e.g. with hyperparasitoids, pathogens or “hitchhikers”). Screening should be done either in the exporting country (preferably in quarantine conditions) just before shipment or in an intermediate country with an approved quarantine facility. Direct releases of natural enemies collected in the region of origin should be avoided. In the event that accidental contamination is discovered in either the exporting, intermediate or importing country, rapid communication between contracting parties should address the issue before further shipment occurs. Any plant materials accompanying the contaminated consignment, as well as the packaging, should be destroyed or sterilized, as per border quarantine operating procedures (if these are in place). Hyperparasitoids should be killed and sent for identification. As a quality assurance and validation measure, at least one generation of the BCA should be completed in containment (in as secure a facility as possible, given that quarantine facilities are unavailable) before release. This will help ensure that BCA specimens are not carrying pests or diseases.

4.4 Rearing and multiplying biological control agents in quarantine

Imported BCAs should always be reared in quarantine through at least one generation to continue screening for contaminants (including hyperparasitoids).

In most cases, multiple generations will need to be reared to produce sufficient numbers of the BCA to test host specificity, for other studies (see section 4.5) and for release (if approval is granted). Usually, a BCA is reared on its target host species (i.e. the pest species); a population of the pest will be required, therefore, in the quarantine facility. Depending on the pest, it may be necessary to maintain live plant material for it to feed on. In this case, good practice is to grow the plant material in a quarantine greenhouse so that clean plants can regularly and securely be brought into the quarantine facility. In the absence of a greenhouse in the quarantine facility, an alternative secure greenhouse may be used, as long as adequate steps are taken to ensure no contaminating pests or diseases are brought into the quarantine facility.

In certain cases, an insect pest may be reared on an artificial diet. Such diets are feasible for wood-boring insects such as the emerald ash borer (Agrilus planipennis) and for defoliating moths such as the gypsy moth (Lymantria dispar). These diets may be modified to suit other insects with similar niches (e.g. other wood-borers and defoliators). Rearing an insect pest on artificial diets is easier than growing plant materials, but this option is not always available or suitable for BCAs.

Methods for rearing BCAs vary by species, and a basic understanding of a BCA’s biology and its insect pest host is required for a successful rearing programme. Box 8 lists key biological characteristics that need to be understood for rearing an insect pest and its BCA.

Ideally, the necessary information for rearing a BCA and the target pest should be obtained before the BCA is imported. This may be available in published literature or reports or from studies in the BCA’s native range linked to the effort to introduce it. If no information on the BCA or pest can be obtained, biological studies will be needed in the quarantine facility. These should occur concurrently with efforts to multiply the BCA, with both activities dependent on the other.

4.5 Assessing the risk of introducing a biological control agent

The risks (likelihood and impact) associated with introducing a BCA to a new area should be fully understood before the BCA is released. For this, a risk assessment should be undertaken.

Growing awareness of the potential adverse effects of BCAs has prompted regulations and methods for risk assessment, the aim of which is to ensure that any non-native natural enemies introduced to an area are safe. A proper evaluation of the potential economic, social and environmental risks is now standard procedure.

The Internet Book of Biological Control (van Lenteren, 2012) describes the environmental risk-assessment process for introducing natural enemies. Some countries, such as Australia, New Zealand and the United States of America, have specific national regulations governing risk-assessment processes. When sufficient information is available, risk assessments may be conducted before a BCA is imported into quarantine.

The risk of introducing a BCA may be indirect or direct:

•Indirect effects are impacts on ecological communities or ecosystem processes through changes to the composition or structure of the food web (e.g. competition for food or space). For example, an introduced BCA may compete with native insects for the same resources (prey or host), resulting in a decline in native insect populations or the reduced suppression of the target pest. Although indirect effects should be considered, they can be difficult to test before the release of a BCA.

•Direct effects include impacts on non-target species, such as consumption, infection or parasitization by the BCA, and the hybridization of the BCA with a native species (which could affect the fitness, behaviour or ecology of the hybrid progeny). Introducing parthenogenetic biotypes is considered a solution to the issue of hybridization (Box 9).

The most commonly considered risk associated with introducing a BCA is the potential for the BCA to prey on or parasitize non-target species. Host-specificity tests are used to evaluate this risk.

Host-specificity and related studies

The aim of host-specificity studies is to identify potential non-target effects caused by introducing a BCA: in particular, they assess and predict whether a BCA will prey on or parasitize native (non-target) species or other species of concern and thereby reduce their populations. A list of non-target species should be developed for testing in consultation with taxonomists or experts in the target species’ taxonomic group.

The study of other potential non-target effects is highly recommended. These might include:

•negative food-web effects (e.g. competition for prey, apparent competition, and displacing native species);

•positive food-web effects that benefit non-target species; and

•the potential for an introduced natural enemy to hybridize with native species.

Criteria exist for determining the non-target species that should be subject to testing (Box 10); other factors include the availability of such species and the potential for rearing them successfully in quarantine.

Sometimes a potential non-target species cannot be reared in a laboratory and therefore cannot be tested in quarantine. In this case, permission may be requested from the NPPO or other relevant government authority to conduct semi-quarantine tests (e.g. within field cages) as an interim stage between importing it into quarantine and releasing it into the environment. Because this approach increases the likelihood of a BCA escaping accidentally, however, strict risk-management measures must be put into place.

Methods for testing host specificity

Behavioural and developmental studies. Host-specificity studies assess the impacts of the behaviour of BCAs on non-target species. For a parasitoid BCA, for example, observations should include the presence or absence of oviposition behaviour towards the non-target species and whether the BCA can develop on the non-target species. The development of a BCA can be categorized into:

•incomplete development – in which BCA development continues only to a certain incomplete life stage; and

•complete development – in which a BCA completes its life cycle on the species.

For both behavioural and developmental studies, it is essential that the target species is included as a positive control to confirm that the testing method is sufficient. For example, if a BCA does not show positive behaviour towards the target host or does not complete its development on the target host, then the experimental design is flawed and should be reviewed. The conditions for studying different treatments, such as tests on non-target and target (control) species, must be standardized. This includes standardizing factors such as host age, mating and feeding history, and host biotype; for example, the same population of a BCA should be used for testing all the test species.

Choice studies. Both choice and no-choice studies can be used in host-specificity tests.

•Choice studies expose a BCA to a number of non-target species (and usually also the target species) simultaneously. Results indicate which species are preferred hosts.

•No-choice studies involve exposing a BCA to one host at a time to determine whether the BCA will develop on the host, even if it is not preferred.

Variations of choice and no-choice tests are available. No-choice tests should be performed first because, when these are negative, it can be assumed that choice tests are unnecessary.

Interpreting the results of host-specificity tests

If a BCA shows no interest in non-target species and does not develop on them, it can be considered host-specific. Note, however, that the degree of host specificity can never be stated with absolute certainty under laboratory or controlled conditions because it depends on the non-target species selected, which in turn is limited by current knowledge and the availability of species for testing. Nevertheless, host-specificity studies should provide good evidence of the likely specificity or non-specificity of an intended BCA.

If a BCA develops completely or partially on one or more of the non-target species tested, or shows interest (for example, oviposition) in any of the non-target species, further consideration and experimentation may be required. A case can still be argued for host specificity if a BCA attacks a non-target species but does not complete development; further experiments are advisable, however, to confirm the lack of full development.

When there is complete development on a non-target species, the suitability of that BCA should be reconsidered. Decisions on the suitability for release of a BCA should also take other factors into account, such as the:

•preference of the BCA for the non-target species;

•likely impact of the BCA on that species; and

•likelihood of the BCA encountering that species in the field.

These factors will require investigation.

The methods used for host-specificity tests should be planned carefully and documented clearly.

As well as studies on a proposed BCA’s host specificity and biology, studies should be undertaken to determine whether the BCA is likely to have an impact on the pest population. In most cases, such studies assess the levels of parasitism or predation achieved by a BCA. Although study results may not accurately reflect parasitism or predation levels in the field, they can provide an indication of the likely effectiveness of a BCA (see Chapter 5).

Occasionally, non-target effects can have unexpected benefits, such as when an introduced BCA also attacks a non-target non-native pest species (Box 11).

4.6 Releasing biological control agents from quarantine

Releasing a BCA from quarantine is a major decision. In a CBC programme, the research and study phases, as well as importing a BCA into quarantine, can all be stopped at any time without significant impact. Releasing a BCA from quarantine, however, is the point of no return.

Applying for release

An application to release is made to the NPPO or other relevant government authority when the results of host-specificity and other studies (see section 4.5) indicate that the intended BCA is suitable for release. When a direct release is planned, it may be possible to obtain import and release authorization in a single application. BCA release-approval applications are not standardized. To help the application, as much relevant information as possible should be provided about the BCA release. National policies and relevant documentation should be consulted in preparing the release application. Suggested topics to include are as follows:

•a brief background of the target insect pest, including its impact and any control options available;

•the value of, and need for, the proposed BCA;

•a description of the proposed BCA, including taxonomy, biology, origin, recorded host species, and any regions in which the BCA has previously been released;

•results of host-specificity and related studies – these will include any known possible indirect ecological effects of the proposed BCA;

•data and discussion on the efficacy of the proposed BCA against the target pest;

•a cost–benefit analysis comparing current or potential losses (economic, social and environmental) from the pest with the expected benefits of releasing the BCA;

•in the case of expected non-target effects, a discussion of the possible environmental impacts and a benefit–risk assessment; and

•the proposed release strategy, including:

- the number and location of the intended release sites

- for insect BCAs, the number of individuals to be released at each site

- the frequency of releases (whether a single release or multiple releases)

- the organizations and facilities involved in rearing the BCA

- the time required to rear the BCA (predefined or long-term)

- any need for further BCA imports.

Data on pest population levels

The release strategy should include baseline data on the pest population as it is before the initial release (“pre-release survey”). This enables comparisons of pest population levels before and after release. The method used for collecting pest population data in before-release and after-release surveys, preferably at the same sites, should be consistent.

Confirming identity of the biological control agent before release

A BCA’s identity to species level should be reconfirmed before release, and voucher or reference specimens should be retained and deposited with at least two key national organizations. Reference specimens can be used to ensure that any future introductions in the same or other areas are of the same species (see section 4.3). Potentially, reference specimens can also be used to determine whether different lineages of the same BCA species have been released. Where possible, reference specimens should be stored in a freezer in 96 percent ethanol for potential future comparisons of DNA sequence data.

Releasing biological control agents into the field environment

When a BCA has already been released in a different area, details of the release method may be available. Otherwise, the process for release can be developed by referring to previous releases of similar BCAs and/or by conducting field trials. The “propagule pressure” – that is, the number of BCA individuals (for insect BCAs) released per site and the number of release sites – can differ between species and areas because establishment depends on the interaction between the founding population and the environment. It is important, therefore, to document all information pertaining to a release and to consider such information in planning post-release monitoring (see Chapter 5).

Regulatory requirements

Before the initial BCA release, an official authorization to perform field releases must be obtained from the NPPO or other relevant authority.

Communication strategy

A clear communication strategy is essential for informing and engaging stakeholders potentially affected by a release, including farmers, producer organizations, forest companies, researchers, universities, neighbouring countries and the public. The NPPO or other authority has primary responsibility for communicating with all relevant parties on a BCA release. Releasing BCAs can be highly contentious, and it is important for stakeholders to support the communication efforts of the NPPO or other authority as much as possible.

Selecting sites for release of biological control agents

The selection of an initial release site should take into consideration the BCA’s preferred habitat and the density of the target pest. Potential sites should have easy, unrestricted access, and they should have no recent (or planned) intensive pest-control activities.

Initial release sites should be used for validation experiments, such as:

•evaluating a BCA’s parasitism or predatory capacity in field conditions;

•climatic or weather effects during and after release;

•BCA establishment and spread; and

•tree recovery.

To facilitate such assessments, the exact release points should be marked (e.g. with stakes) and the coordinates recorded using a global positioning system device.

Newly released BCAs are likely to have been reared in laboratory conditions in a quarantine facility and may be especially sensitive to unfavourable weather in the field-release environment. The release should be timed to ensure, as much as possible, that optimum weather conditions apply. In many cases, failure to establish a BCA in a region is related directly to previous applications of chemical insecticides. It is important, therefore, to select release sites that have not recently been sprayed with insecticides or other toxic chemicals.

Methods for releasing biological control agents

There are various methods for releasing BCAs in the field. The method selected should be matched to the type of natural enemy and its life cycle and dispersal mechanism and the developmental stage at which it is collected and shipped. It is important that the phenology of a BCA is synchronized with that of the pest when deciding on the timing and method of release.

Conditions during release. Ideally, BCAs should be kept cool (but not cold) and shaded during transportation, with adequate ventilation in containers to avoid condensation. Survival rates can be improved by providing food sources (e.g. pollen or nectar for parasitoids) during transportation and at the release site. In general, BCAs should be released when temperatures are moderate (e.g. in the morning or late afternoon/early evening on hot days and at midday on cool days); insect BCAs should not be released on rainy days.

Insect BCAs. The simplest way to release insect BCA larvae, nymphs or adults into the field environment is to tap an opened container onto a pest-infested host plant. The BCAs should fall out or emerge and seek out the pest. Adults will disperse, so one release point (e.g. a single plant) per site is often sufficient. On the other hand, actively feeding immature stages are less mobile and should be scattered on several plants to ensure they can find sufficient food.

Pathogen BCAs. For fungal pathogens in particular, the preferred release methods are to:

•spray or dust several pest-host plants with a suspension of spores in water; or

•place presprayed plants in pots at the release site.

In both cases, the pathogen’s humidity requirements should be met for the first 6–8 hours. This means that either release should occur on a misty or rainy day, or the treated plants should be misted and covered with plastic bags overnight to maintain humidity.

Spores will wind-disperse and travel long distances from the initial point of release.

Release methods for pathogenic nematodes differ from those for fungal pathogens; see case study 7.8 for the release method used for BCAs of the sirex woodwasp.

Aerial application. When a target area is large or the terrain difficult, BCAs may be released aerially. Planes and helicopters used in conventional aerial pest-control operations are being replaced by drones for this purpose because they are more flexible and cheaper to operate.

Post-release establishment. To enable BCA populations to establish and grow, attention should be paid to the release site for a certain period after release to ensure that:

•the site is not sprayed with insecticide;

•plants are not destroyed; and

•plants or plant parts that support the BCA’s life cycle are not removed.

Use the data collected and lessons learned from an initial release to increase the effectiveness of subsequent releases in other areas. Steps should be taken to ensure that sufficient BCAs are reared for wider release areas.

Rearing procedures for further releases of biological control agents

Researchers should develop protocols for rearing BCAs in quarantine. For field releases, these protocols should be adapted to reproduce a given BCA on a larger scale outside the quarantine area once permission to release has been granted. If possible, BCAs for release should be reproduced in insectaries inside greenhouses or screened cages. Alternatively, it might be possible to recover BCAs directly from post-release field sites and to transfer them to new release sites.

5 Monitoring and evaluating classical biological control

5.1 Post-release monitoring

Monitoring BCA performance during pre-release, release and post-release is a crucial final step in implementing a CBC programme. Accurate monitoring will ascertain the effectiveness and impacts of a BCA, enable ongoing comparisons between regions, and help improve future programmes.

A post-release monitoring system includes:

•sampling methods for the BCA and target pest;

•monitoring procedures to regularly observe, measure and record the BCA’s populations, dynamics, weather, host-tree conditions (e.g. pest damage symptoms), pest populations, infestation levels and potential competitors or natural enemies of the BCA; and

•assessing non-target effects of the BCA.

In developing sampling methods, it is useful to identify population benchmarks for both the BCA and the target pest. Such benchmarks can be described using the following parameters of population expression:

•population density – the number of individuals per available food resource (e.g. host or prey insects for BCAs and leaves, buds, seeds, fruit or biomass for herbivorous insects);

•relative population – the number of individuals per sampling unit (e.g. tree canopy or trap) – samples might be collected using knockdown insecticides (in a small area or tree canopy) or traps (e.g. light traps and sex or aggregation pheromone traps); and

•population indexes – indirect measures of insect density such as frass weight, damage severity and percent defoliation.

Population density and relative population are the best parameters for BCA population expression, and population density can be used to estimate parasitism (Box 12) and predation. Relative population is useful when a BCA cannot be sampled directly from its host, for example when the tree canopy is very high.

Before setting traps to capture BCAs, previous studies should be consulted to evaluate the best trap designs and tree position(s). Malaise traps and coloured sticky traps are suitable for many insect parasitoids.

Population indexes can be used to assess pest populations when it is difficult to apply other sampling methods. These are easier and less time-consuming to use, although they require more time for verifying differences in pest symptoms and signs. In most cases, population indexes are unreliable for correlating a reduction in pest population with true BCA effectiveness, but they are useful for evaluating defoliation (e.g. by Gonipterus weevils) and gall severity (e.g. gall-wasp infestations).

Once the sampling methods have been decided, monitoring procedures should be determined for the selected sites. Monitoring data can be used to understand the dynamics of a pest population and the climatic and seasonal factors that affect it. To ensure consistent results, the same monitoring procedures should be used at all sites where a pest has been identified. Assessing data from ongoing monitoring efforts ensures the accurate measurement of BCA effectiveness, pest reductions and non-target effects.

Effectiveness of biological control agents

Assessing the effectiveness of a BCA can start in the early stages of introduction to help indicate the likelihood of ongoing success. Key assessment parameters are:

•Establishment

•Population growth

•Dispersal.

These parameters are assessed by monitoring BCA numbers:

•over time – to assess establishment and population growth; and

•within and beyond the introduced area – to assess dispersal.

Results will help determine whether the level of establishment, population growth and dispersal of a BCA is likely to suppress the target pest to below the desired economic or environmental threshold.

Biological control agent establishment. The failure of a BCA to establish may be due to reasons unassociated with the BCA’s suitability. Releasing a low number of individuals is a common reason for failing to achieve establishment. Other causes influencing the survival of the initially released populations include competition with other insects; predation and parasitism; unsuitable release timing; and severe weather events following release. If the first population is too small, either because too few individuals were released or because of high mortality after release, the population may go extinct due to the “allee effect” – which occurs when the population is very small or highly dispersed in its new environment, reducing the likelihood that individuals will encounter the opposite sex, mate and reproduce.

In many cases, the factors affecting BCA establishment can be overcome by changing the:

•size of each release to find the optimal release size;

•number of releases (frequency);

•release season; or

•release method (for example, releasing different developmental stages).

Note that, in rare cases, BCA populations have established successfully despite their release in small numbers (ten or fewer individuals).

Biological control agent population growth. Established populations of a BCA may be difficult to detect at first, particularly when survey procedures are inadequate (e.g. sample sizes are too small). There may be a time lag between a field release and recording the presence of a BCA, with some BCAs remaining at low and sometimes undetectable densities for several generations after release. This is referred to as the “eclipse period” (also “lag phase”), when populations stay small while the BCA adapts to local conditions. Although populations of some BCAs grow very fast, others will require several years to reach population sizes capable of having an impact on a target pest. The number of generations produced per year will influence the speed at which populations grow.

Biological control agent population dispersal. High dispersal ability is a desirable attribute of BCAs because it enables faster control of a pest population and reduces the number of release points needed. A high dispersal ability can, however, also reduce the abundance of a BCA, both at the release site and at non-release sites, due to migration and an “area dilution” effect. In this case, population density will decline towards the margins of the geographical range of expansion because individuals spread out over a progressively larger area.

A BCA with low dispersal ability will require greater effort to ensure that it spreads throughout the introduced range, likely increasing the cost of the CBC programme. This, however, should not be a reason for dismissing the BCA from the programme.

Pest reduction

Pre-release surveys, combined with pest monitoring, will confirm whether pest numbers have declined, but this reduction may not be due to the BCA alone. Year-to-year pest abundance can vary substantially due to climatic fluctuations, land-use change, tree susceptibility, forest practices and the impacts of native natural enemies. To make objective assessments of the impacts of BCAs, standardized quantitative surveys need to be repeated over time.

Temporal comparisons. It is desirable to collect pre-release data for pest damage and the effectiveness of native natural enemies to enable temporal (“before and after”) comparisons for assessing the effectiveness of a BCA release. For example, a CBC programme in Italy was implemented against the Asian chestnut gall wasp (case study 7.3) that had caused a significant (up to 80 percent) decrease in chestnut yields. Monitoring of native parasitoid efficacy at different sites showed that, 3–5 years after the arrival of the pest, the average rate of parasitism was very low (0.45 percent). A few years after the release of the BCA Torymus sinensis, its efficacy was estimated by considering chestnut production recovery (at least 50 percent of the values observed before the pest’s arrival) and the high mortality inflicted on the pest by both the BCA (up to 90 percent) and native parasitoids (2 percent).

Spatial comparisons. A pest reduction caused by a BCA can be confirmed by comparing areas where the BCA is already present with areas where it is absent (spatial “with and without” comparisons). This is particularly useful when pre-release data are insufficient for carrying out a temporal comparison, for example when serious damage caused by an invasive species requires urgent action.

Both spatial and temporal comparisons should ideally be carried out to assess pest- reduction rates and the impact of a released BCA.

Non-target effects

As stressed in section 4.5, it is important to determine whether a BCA introduction will have a positive, negative or neutral impact on local ecosystems. After release, there is an opportunity to confirm the validity of pre-release risk assessments and tests on host-range impacts. For example, a post-release monitoring study was carried out in North America on the BCA Peristenus digoneutis, which is an egg parasitoid of Lygus plant bugs. The study revealed that the impact of the parasitoid on non-target species was significantly less than predicted by laboratory analysis. Nevertheless, BCA releases can have negative non-target impacts (Box 13).

5.2 Evaluating the success of a classical biological control programme

The success of a CBC programme is determined by the extent to which it meets the objective of safely reducing the impacts of pests on trees and the environment. The reduction of pest numbers to an acceptable threshold, and limited non-target effects, would be indicators of a successful CBC programme. The extent of success can be better understood by answering the following three questions:

1. To what extent has the BCA been effective, and why?

2. To what extent was the pest reduction caused by the BCA or other factors?

3. What was the extent of any non-target effects?

It must be noted that even partial success (e.g. a reduction in pest density that remains permanently or occasionally above a threshold level) may have a positive effect if it reduces the use of costly or unsustainable pest-control methods.

Another aspect to consider in determining the success of a CBC programme is how well it has been implemented. Analysing the implementation of each step of the programme will provide a greater understanding of the extent of its success and help in identifying ways to improve future programmes. Questions about a CBC programme’s implementation might include:

•Has the programme gone according to plan?

•How effectively and efficiently was each step in the programme carried out, including the accuracy of assessments and studies undertaken, the communication strategy and other social considerations?

•Has stakeholder engagement been appropriate?

•Has the cost of the programme kept within the allocated budget?

Assessing the impact of a classical biological control programme

In addition to assessing the success of a CBC programme, its wider impact should also be determined, including its economic, social and environmental benefits. Relevant questions include:

•Has the CBC programme resulted in increased or restored forest production?

•Has the pest reduction led to a reduction in insecticide use?

•Have jobs been created or protected?

Estimating all the benefits of a CBC programme will increase the credentials of future programme proposals.

6 Other considerations

6.1 The Nagoya Protocol

The Nagoya Protocol on Access to Genetic Resources and the Fair and Equitable Sharing of Benefits Arising from their Utilization, a supplementary agreement to the Convention on Biological Diversity (CBD), came into force on 12 October 2014. The CBD recognizes that countries have sovereign rights over genetic resources within their boundaries and that CBD parties have the authority to determine access rights to these genetic resources. The Nagoya Protocol provides a framework for the fair and equitable sharing of benefits arising from the use of genetic resources, including BCAs used in CBC programmes against forest insect pests.

CBC involves the release of living organisms into new environments. BCAs that become established, reproduce and spread will have a self-sustaining effect on target pests. Such BCAs thus become “common goods” available to all, and CBC programmes must comply with regulations governing access and benefit-sharing arising from the Nagoya Protocol.

Countries that have signed up to the Nagoya Protocol are required to develop and introduce frameworks to ensure shared access to genetic resources, benefit-sharing and compliance. Many signatory countries allow free access as part of their frameworks, but some place restrictions on the import or export of genetic resources, including BCAs. These restrictions can hinder the successful implementation of CBC in managing transboundary pests.

FAO, the CBD, the Centre for Agriculture and Bioscience International and the International Organisation for Biological Control (IOBC) work to promote the use of BCAs under special considerations of the Nagoya Protocol and to facilitate compliance with the Protocol. The IOBC provides guidelines for best practices that maintain continued, legitimate access to BCAs for research and use as a public good.

6.2 Stakeholder engagement

The importance of the ongoing involvement of, and meaningful communication with, all stakeholders throughout the course of a CBC programme cannot be overstated.

In many countries, stakeholder engagement on the implementation of CBC is conducted by NPPOs or other relevant national organizations. Very early in the process (even before a BCA is imported into quarantine) it is beneficial to develop a communication plan jointly with the NPPO or other relevant organization and to identify all the affected stakeholders, including the public.

Good stakeholder communication is very important in forestry, where large, highly biodiverse areas are often subject to pest management. A lack of communication can result in misconceptions about the impacts of a CBC programme, and miscommunication can lead to barriers to the use of CBC as an option in IPM.

Compared with other pest-control methods, the benefits of CBC as a self-sustainable, long-term pest-management option are often less apparent and underestimated. Also, the risk-assessment process for introducing BCAs must be transparent. At the beginning of a CBC programme, the process should be explained clearly to all stakeholders, including forest practitioners and managers, non-governmental organizations and the public, through training workshops, farmer field schools and the media and by distributing fact sheets about the programme. A participatory approach is the best option for implementing CBC programmes.

6.3 The way forward

As shown in this guide, implementing an effective CBC programme is a multistep process requiring a highly coordinated approach by a wide range of actors and organizations, including regulators, scientists, forest managers and practitioners. Many countries that would benefit from effective CBC programmes lack access to the required knowledge and resources. Ongoing collaboration and information-sharing between countries, as well as regionally and globally, is vital, therefore, for ensuring successful CBC outcomes. Stakeholder consultation and participation is also essential: CBC works best when it is inclusive and championed by many.

Several national and regional organizations and networks, including working groups of the IOBC, promote CBC as part of IPM and actively encourage the sharing of information and resources. Such organizations also encourage participation, and membership is open to representatives of countries and organizations as well as to individuals. The knowledge gained, support given and assistance provided is invaluable for preventing, detecting and managing forest insect pest outbreaks.

In looking ahead, it is important to consider the role that all stakeholders can play in challenging negative perceptions of CBC, which may exist due to the adverse environmental impacts of past CBC programmes. It is crucial to ensure that future CBC programmes are based on sound scientific data and analysis and best management practices and to communicate this to the public. There is a need to promote CBC and its successes widely to ensure its greater acceptance among scientists, forest practitioners, the public and decision-makers. This, in turn, will help ensure the safe and effective deployment of CBC in the world’s forests.

7 Case studies

7.1 Coconut rhinoceros beetle in the Pacific region

Insect pest: Oryctes rhinoceros L. (Coleoptera: Scarabaeidae)

Biological control agent: Oryctes rhinoceros nudivirus (OrNV)

Insect pest

The coconut rhinoceros beetle (Oryctes rhinoceros – CRB), a native of Southeast Asia, is a major invasive pest of coconut and oil-palm trees in the Pacific region. The adult beetle bores into the crowns of palms, where it damages growing tissue and feeds on tree sap, cutting across young fronds and flowers. This reduces leaf area, causes early nut fall, decreases yields and creates open wounds that can become infected by decay organisms. The damage significantly reduces production and can lead to tree death.

Biological control programme

CRB has been managed successfully in the Pacific since the 1960s using a viral BCA, Oryctes rhinoceros nudivirus (OrNV), as part of IPM. OrNV was discovered in Malaysia in the nuclei of CRB larval fat-body cells and the nuclei of midgut epithelium cells (of larvae and adults), as well as in the adult ovarian sheath and spermatheca. The virus is transmitted orally and also deposited in feeding sites through beetle faeces. Once infected, larvae die within 1–4 weeks. The virus did not exist in any South Pacific country before its introduction as a BCA in the 1960s.

Impact of classical biological control

This is an example of the highly successful, practical use of an insect virus in CBC, and it is a landmark case. The virus has established successfully at many sites in Fiji, Mauritius, Papua New Guinea, Tokelau and Tonga and on the Samoan islands and Wallis Island. It significantly reduces beetle damage to palms within 1.5 years of establishment.

After 40 years, some Pacific Islands with established CRB populations – such as Guam, Hawaii, Palau, Papua New Guinea and Solomon Islands – reported an increased severity and frequency of damage caused by CRB. Attempts to introduce OrNV into the Guam CRB population have been unsuccessful, and it is possible that the CRB population biotype on Guam is tolerant of or resistant to OrNV isolates. Efforts are underway to identify a virus in CRB’s native range that will be effective against the newly described biotype CRB-G.

Key lessons

•The use of a virus in a CBC programme can cause persistent pest suppression over time.

•To achieve a virus’s optimal control capacity, it is essential to comply with IPM principles.

•To maintain high levels of control, additional biotypes of a BCA may be required over time or for different populations of the pest.

Further reading

Huger (2005); Jackson (2009).

7.2 Great spruce bark beetle in Europe

Insect pest: Dendroctonus micans Kugelann (Coleoptera: Curculionidae, Scolytinae)

Biological control agent: Rhizophagus grandis Gyllenhal (Coleoptera: Rhizophagidae)

Insect pest

The great spruce bark beetle (Dendroctonus micans) lives under the bark of spruce trees (Picea spp.) and is sometimes found in other conifers. It is probably native to northern Siberia, but it has spread westward over the past 100 years. D. micans was first noticed in Belgium in 1897 and in the United Kingdom of Great Britain and Northern Ireland in 1982, where it caused significant mortality to sitka spruce (P. sitchensis). The beetle is still expanding its range, although it has not yet reached Ireland or Spain. From the Russian Federation it has also spread southward: it was first recorded in Georgia in 1957, from where it entered Turkey. Under endemic conditions, the beetle is widespread but causes only minor damage, and outbreaks occur mainly on the edges of its expanding range, where heavy tree losses due to repeated attacks have been observed.

Biological control programme

The first biological control programme was developed in the Georgian Soviet Socialist Republic in the 1960s, a few years after the pest was detected in the region and where it caused severe damage to oriental spruce (P. orientalis). A predatory beetle, Rhizophagus grandis, specific to D. micans, was known to control bark beetle populations in central Europe. Adults of R. grandis are attracted by volatiles in frass produced by D. micans and lay eggs among the prey’s brood. R. grandis larvae and adults feed on the eggs and larvae of D. micans in their galleries. This predator, imported from Czechoslovakia, was released in Georgia as a BCA, with a series of rearing units set up to further distribute the species. A similar CBC programme was later implemented in Turkey.

CBC programmes to combat D. micans were set up in central and western France and the United Kingdom of Great Britain and Northern Ireland in the 1980s, and hundreds of thousands of R. grandis specimens were produced and released. With D. micans continuing to spread in both countries, R. grandis is still being released regularly in newly infested areas.

Impact of classical biological control

Rhizophagus grandis has established quickly in all areas in which it has been introduced, and pest outbreaks have usually collapsed within 6–10 years. In France and the United Kingdom of Great Britain and Northern Ireland, there is a strong link between reduced pest populations and the increased predator levels encountered in the main infested areas.

Key lessons

•Natural enemies do not always closely follow their host or prey when a pest is invading new areas. In such cases, CBC is appropriate to assist natural enemies in their spread and to restore natural control.

•Although many predators are generalists and thus not suitable for CBC, some are very specific to their prey and can be used successfully as BCAs.

Further reading

Fielding and Evans (1997); Grégoire (1988).

7.3 Asian chestnut gall wasp in North America, northern Asia and Europe

Insect pest: Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae)

Biological control agent: Torymus sinensis Kamijo (Hymenoptera: Torymidae)

Insect pest

The Asian chestnut gall wasp (Dryocosmus kuriphilus) (ACGW) is a specialist gallmaker on chestnuts (all Castanea spp. and their hybrids) native to China. After its accidental introduction to Japan, the Republic of Korea, North America and Nepal (in the 1940s, 1950s, 1970s and 1990s, respectively), the ACGW arrived in northwestern Italy in 2002 and spread rapidly throughout Europe. Parthenogenetic females emerge in summer and lay eggs in newly developed chestnut buds, where the larvae overwinter. In spring, attacks by the ACGW cause galls to form on growing leaves and shoots, potentially damaging tree growth and reducing fruit, wood and honey production. Moreover, trees weakened by intensive ACGW attacks are likely to be highly susceptible to other disturbances, such as drought and infection by pathogens.

Biological control programme

Native parasitoids in invaded countries have been unable to control the ACGW, due largely to mismatches in life cycles. To control the ACGW, therefore, extensive CBC programmes have been implemented in Japan, the United States of America and, more recently, Italy to introduce Torymus sinensis, a parasitoid specific to the ACGW in China. T. sinensis has one generation per year, like its host, and its flight period coincides with the appearance of the host galls, where it lays eggs. Larvae of T. sinensis develop within the galls, killing the pest larvae before overwintering and pupation. Releases in Italy usually comprised 150 individuals with a female-to-male ratio of 2:1. This propagule size was sufficient to establish the parasitoid successfully at most sites.

Impact of classical biological control

Declines in ACGW populations to below threshold levels of damage were reported in Japan and the United States of America following the introduction of T. sinensis as a BCA – indirect evidence of the parasitoid’s efficacy and its ability to expand its geographic range alongside expanding ACGW populations. In northwestern Italy, parasitism as high as 85 percent was recorded eight years after release of the BCA. In Veneto in northeastern Italy, chestnut stands are distributed over an area of 20 500 hectares, and severe losses in both nut production (down by 80 percent) and wood yield (down by 40 percent) were reported before BCA release. Almost 500 BCA releases were made over six years. The BCA reached non-release sites (via short- and long-distance flights), up to 70 km away from the nearest release site, within 3–5 years of first release. The average mortality inflicted on the pest was 82.5 percent, resulting in a recovery in yield of at least 50 percent. Recent studies have shown that T. sinensis has had minimal impact on non-target cynipid wasps, and it is able to follow fluctuations in the host population in both time and space.

Key lessons

•Specific parasitoids that are well synchronized with their hosts can have a large impact on pest populations.

•BCAs are able to respond to the spatial distribution of hosts, ensuring the rapid colonization of the host’s geographic range.

•Habitat structure (e.g. resource concentration, such as host-containing patches and food) can play a fundamental role in the rapid establishment, growth and spread of introduced BCAs.

Further reading

Battisti et al. (2014); Colombari and Battisti (2016a); Colombari and Battisti (2016b); Ferracini et al. (2017); Colombari and Battisti (2017).

7.4 Orthezia bug on Saint Helena

Insect pest: Insignorthezia insignis Browne (Hemiptera: Ortheziidae); syn: Orthezia insignis Browne (Hemiptera: Ortheziidae)

Biological control agent: Hyperaspis pantherina Fürsch (Coleoptera: Coccinellidae)

Insect pest

The orthezia bug (Insignorthezia insignis) is a polyphagous scale insect from South and Central America that is now widespread throughout the tropics. It has been controlled successfully in Hawaii, several African countries and Peru using its specific predator, the coccinellid beetle (Hyperaspis pantherina). In 1991, the orthezia bug was found to have severely affected the endemic and highly valued gumwood tree (Commidendrum robustum) on the small South Atlantic island of Saint Helena. At the time of this first record, the gumwood population was restricted to 2 000 individuals. Two years later, 400 of the 2 000 had been killed.

Biological control programme

In collaboration with international organizations, the Government of Saint Helena, Ascension and Tristan da Cunha initiated a CBC programme immediately after the damage was discovered. The H. pantherina beetle was collected in Kenya, where it successfully controls the same scale on other trees. The collected specimens were imported to the United Kingdom of Great Britain and Northern Ireland for quarantine studies, which showed that the predator lives and develops in close association with the orthezia bug and is probably specific to it. Because no closely related indigenous scales are present on Saint Helena Island, releasing the coccinellid beetle there was considered safe for the environment.

Impact of classical biological control

The introduction of H. pantherina on Saint Helena resulted in the rapid collapse of the orthezia bug population. Within two years, mean orthezia bug numbers per 20-cm branchlet had decreased from more than 400 adults and nymphs to fewer than 15. Outbreaks of the scale have not been observed since 1995, and H. pantherina is considered to have averted gumwood’s extinction. This is probably the first CBC programme implemented for the purpose of saving a tree from extinction.

Key lessons

•As well as being effective for commercial crops, CBC can be a valuable management method for protecting the environment against invasive pests.

•Fast reaction is essential to save trees endangered by an invasive pest.

•Previous CBC successes can serve as the basis for planned new CBC programmes.

Further reading

Cock et al. (2015); Fowler (2004).

7.5 Eucalypt gall wasp

Insect pest: Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae)

Biological control agents: Quadrastichus mendeli Kim & La Salle (Hymenoptera: Eulophidae); Selitrichodes kryceri Kim & La Salle (Hymenoptera: Eulophidae); Megastigmus zvimendeli Doganlar & Hassan (Hymenoptera: Torymidae); Megastigmus lawsoni Doganlar & Hassan (Hymenoptera: Torymidae); Selitrichodes neseri Kelly & La Salle (Hymenoptera: Eulophidae)

Insect pest

Leptocybe invasa is a small wasp (1–1.5 mm in length) of presumed Australian origin that induces galls on the leaf midribs, petioles and stems of susceptible Eucalyptus species. It was first detected in the Middle East and Mediterranean in 2000, and within ten years it had spread to all regions of the world in which eucalypts are grown. Damage can range from the complete write-off of plantations at establishment (caused by heavy seedling malformation) to negative impacts on growth rates in young trees.

L. invasa mainly reproduces parthenogenetically, and males are found only rarely. This ability to reproduce asexually has contributed significantly to the species’ success as a highly invasive pest. The spread of the wasp has also been assisted by the movement of infested nursery stock around the world. Another – currently undescribed – species of Leptocybe is also spreading; in many areas it co-occurs with L. invasa. The two species are morphologically indistinguishable and can only be identified with molecular barcoding.

Biological control programme

Israeli scientists carried out surveys of Leptocybe-like galls in eastern Australia in 2006, collecting four parasitoids to use in Israel’s CBC programme – two eulophid wasp species, Quadrastichus mendeli and Selitrichodes kryceri, and two torymid wasp species, Megastigmus zvimendeli and M. lawsoni. These four parasitoids were released in Israel in 2007. A South African scientist discovered a fifth parasitoid, Selitrichodes neseri, in Australia in 2010, and this was released in South Africa in 2012 and Brazil in 2015 and then in a number of other countries in Africa and South America.

Impact of classical biological control

All four parasitoids released in Israel became established and are now exerting substantial control over L. invasa there and in most of the Mediterranean region. Quadrastichus mendeli and M. zvimendeli appear to be the most successful and abundant of the four parasitoids, but all four are helping reduce population densities of L. invasa in Israel. Initial data show that S. neseri has established successfully in South Africa and Brazil, and its establishment in other countries is being assessed. Q. mendeli has been recorded moving unassisted to several parts of the world, including Africa and Southeast Asia. In some locations, apparently native parasitoids have switched to L. invasa as a host and are contributing significantly to the control of pest populations.

All parasitoids so far released against L. invasa have been collected on another, undescribed species of Leptocybe in Australia (L. invasa is yet to be found in Australia). The short- and long-term impacts of this on the biocontrol of both Leptocybe species is unknown.

Key lesson

Introducing and releasing multiple parasitoids against an invasive pest may achieve higher and more stable levels of control under a variety of climatic conditions and range of tree hosts. Single parasitoid species, often sourced from a single location in a pest’s endemic range, are less able to adapt to different climates and may also have lower genetic variability.

Further reading

Dittrich-Schröder et al. (2018); Mendel et al. (2004); Mendel et al. (2017).

7.6 Bronze bug on Eucalyptus in Brazil

Insect pest: Thaumastocoris peregrinus Carpintero & Dellapé (Hemiptera: Thaumastocoridae)

Biological control agent: Cleruchoides noackae Lin & Huber (Hymenoptera: Mymaridae)

Insect pest

The bronze bug (Thaumastocoris peregrinus), which is native to Australia, has become a serious pest of eucalypt plantations in Africa, South America and Europe. It was introduced unintentionally to South Africa in 2003, Argentina in 2005 and Italy in 2011, and it spread quickly across Africa, South America and Europe, causing silvering and bronzing in eucalypt canopies and intense defoliation. The bronze bug can infest almost any commercially planted Eucalyptus species and clone. Data from forest inventories of eucalypt plantations in different parts of Brazil over the period 2010–2015 show a reduction in wood production of 10–20 percent and estimated losses of USD 330 million.

Biological control programme

The egg parasitoid Cleruchoides noackae was introduced to Brazil from Australia in 2012, with the first releases in infested plantations in the states of São Paulo and Minas Gerais. Females of C. noackae parasitize T. peregrinus eggs and adults emerge from the egg operculum, making it difficult to evaluate effective parasitism. The life cycle (egg to adult) of C. noackae spans about 16 days at 24 °C, and the adult stage spans 1.1–3.6 days. A new egg-laying technique using paper towels enabled a higher production of pest eggs and parasitoids and, by 2018, the parasitoid had established in four Brazilian states, with more than 250 000 parasitoids reared and released in the country in 2014–2016. Laboratory and field evaluations have shown parasitism rates of 50–60 percent, reaching as high as 90 percent in some places. The parasitoid was introduced to Uruguay in 2015, successfully reducing pest populations in eucalypt plantations there, too.

Impact of classical biological control

The CBC programme successfully reared, released and established the parasitoid in plantations in five areas. Three years after the first releases of C. noackae, the infested area had been reduced by 18.8 percent (compared with 2012). In addition, avoiding the use of chemical insecticides enabled native natural enemies, such as the predatory bugs Atopozelus opsimus and Supputius cincticeps, to assist in reducing pest populations. The CBC programme will continue until the parasitoid has been established in all Brazilian states.

Key lessons

•An egg parasitoid with a lifespan synchronized with its host and well adapted to field conditions can be highly effective in reducing pest populations.

•Enhancing rearing techniques improves the production of BCAs and reduces the time before parasitoids become established and control is effective.

•By allowing a reduction in the use of chemical insecticides, the introduction of successful BCAs helps native natural enemies play complementary roles in pest management.

Further reading

Barbosa et al. (2017); Dias et al. (2014); Mutitu et al. (2013); Soliman et al. (2012); Wilcken et al. (2010).

7.7 Mango mealybug in West Africa

Insect pest: Rastrococcus invadens Williams (Hemiptera: Pseudococcidae)

Biological control agents: Gyranusoidea tebygi Noyes (Hymenoptera: Encyrtidae); Anagyrus mangicola Noyes (Hymenoptera: Encyrtidae)

Insect pest

Mango (Mangifera indica) is a highly valued fruit and shade tree in West Africa. The mango mealybug (Rastrococcus invadens), which originates in Southeast Asia, was first found in Ghana and Togo in 1981. Nymphs and adults affect plant leaves, inflorescences and fruit by sucking the sap, but the main damage is due to the honeydew secreted by the bug. This secretion allows a black sooty mould to develop, which limits photosynthesis and reduces tree growth and fruit production. In Benin, yield losses due to the mango mealybug were estimated at 89 percent. The pest is polyphagous, and attacks have also been observed on other fruits, such as banana and citrus, although mango appears to be preferred.

Biological control programme

Benin’s national authorities developed a CBC programme in 1986 in collaboration with various international organizations. Surveys for natural enemies were carried out in India and Malaysia, and two abundant and previously undescribed parasitoids found in India were sent to the United Kingdom of Great Britain and Northern Ireland for quarantine studies. These parasitoids, later described as Gyranusoidea tebygi and Anagyrus mangicola, occupy different ecological niches: G. tebygi attacks young nymphs and A. mangicola targets older females. Moreover, laboratory tests showed that the parasitoids are specific to the mango mealybug and it was decided therefore to introduce the two species. Releases started in 1987 for G. tebygi and in 1991 for A. mangicola. The two species were later distributed in many countries throughout West and Central Africa from a mass-rearing facility in Benin. They also spread naturally to other African countries and are now present in the entire area occupied by the mango mealybug.

Impact of classical biological control

The results of the CBC programme were spectacular, with mealybug populations dropping significantly throughout West and Central Africa. In Benin, mango production increased by 142 percent. The CBC programme lasted nine years and cost USD 3.66 million, and the benefits were huge. Cost–benefit ratios of 1:145 and 1:808 were calculated for Benin and sub-Saharan Africa, respectively, to 1999 and are likely much higher today. The calculation of the ratios did not take into account the non-monetary value of mango trees for shade and medicine and as a source of energy and vital nutrients for rural communities.

Key lessons

•Two effective parasitoids can be introduced together when they occupy different ecological niches.

•Huge benefits can be achieved with CBC because they persist over time without further action.

Further reading

Cock et al. (2015); Moore (2004).

7.8 Sirex woodwasp in Australasia, Africa, the Americas and Asia

Insect pest: Sirex noctilio Fabricus (Hymenoptera: Siricidae)

Biological control agents: Deladenus (Beddingia) siricidicola Bedding (Tylenchida: Neotylenchidae); Ibalia leucospoides Hochenwarth (Hymenoptera: Ibalidae); Megarhyssa nortoni Cresson (Hymenoptera: Ichneumonidae); Rhyssa persuasoria persuasoria L. (Hymenoptera: Ichneumonidae)

Insect pest

The sirex woodwasp (Sirex noctilio) is native to Europe, North Africa and parts of Asia and has been introduced unintentionally to most pine-growing areas of Australasia, Africa, the Americas and Asia. The sirex woodwasp has become a serious pest of Pinus species when the trees are grown as non-natives in plantations. The wasp introduces a symbiotic fungus (Amylostereum areolatum) and a toxic mucous into pines during oviposition, resulting in the eventual death of the trees.

Biological control programme

The first report of the sirex woodwasp outside its native range was in New Zealand in about 1900; it was reported in Tasmania, Australia, in 1952 and on the Australian mainland in 1961. Increasing infestations of the sirex woodwasp, particularly in Australia, prompted a programme in the 1960s and 1970s to search for BCAs, both in its native range and in North America, where other Sirex species occur. This programme tested a number of natural enemies as potential BCAs.

A parasitic nematode (Deladenus siricidicola) and a number of parasitic wasps were released into the field environment in the invaded range (after considering host specificity, recorded prevalence – effectiveness – on the target host, and suitability for mass-rearing).

D. siricidicola has a bicyclic life cycle. It parasitizes larvae of the sirex woodwasp in the parasitic life cycle and remains in its host until pupation, when it moves to the reproductive organs and infests and sterilizes the female’s eggs. The female wasp oviposits the sterile eggs into host trees, which helps spread the nematode. In the fungus-feeding life cycle, D. siricidicola feeds on A. areolatum (the symbiotic fungus of the sirex woodwasp). The nematode’s life cycle on the fungus lasts only about two weeks, which means large numbers of the nematode can be reared in the laboratory on fungal cultures in a short period. Mass-reared nematodes are dispatched to the infested areas in breathable plastic bags, with water. Polyacrylamide powder is then added to the nematode–water mixture, forming a gel that is inoculated into holes made in infested trees with specialized inoculation hammers.

Of the parasitic wasps introduced as BCAs against the sirex woodwasp, the most successful have been Ibalia leucospoides, Megarhyssa nortoni and Rhyssa persuasoria. The first of these parasitizes the eggs and early larval instars of the woodwasp and the other two parasitize its mature larvae.

Impact of classical biological control

The use of CBC to manage populations of the sirex woodwasp is considered to have been largely successful where it has been applied in Australasia, Africa and South America. In the late 1980s, it was reported that the strain of nematode released previously had lost virulence, possibly because the fungal-feeding form had been cultured for more than 20 years. This prompted the selection of a new nematode strain for release.

The extent of parasitism achieved by the parasitic wasp BCAs is reported to vary between regions with differing climates, and the nematode control method has consequently been applied in some of those areas.

Key lessons

•The ability to mass-rear and effectively apply the parasitic nematode D. siricidicola to infested trees, together with the high rates of parasitism obtained in many areas, contributed to the use of this nematode as the primary BCA of the sirex woodwasp.

•BCAs may lose virulence over time and are not always effective uniformly between areas. It may be necessary, therefore, to release new strains and to adapt local CBC programmes over time.

Further reading

Bedding and Iede (2005); Hurley, Slippers and Wingfield (2007); Slippers, Hurley and Wingfield (2015).

7.9 Winter moth in Canada and the United States of America

Insect pest: Operophtera brumata L. (Lepidoptera: Geometridae)

Biological control agents: Cyzenis albicans Fallén (Diptera: Tachinidae); Agrypon flaveolatum Gravenhorst (Hymenoptera: Ichneumonidae)

Insect pest

The winter moth (Operophtera brumata) is native to Europe, where it is considered a sporadic pest of various deciduous trees. It was introduced unintentionally to Nova Scotia in eastern Canada in the first half of the twentieth century and quickly became a serious pest of forest trees there, particularly oak (Quercus) species but also orchard trees such as cherry and apple. In the 1950s, red oak (Q. rubra) in Nova Scotia suffered a mortality rate as high as 40 percent due to O. brumata outbreaks; later, the moth appeared on the west coast of Canada. In the United States of America, O. brumata appeared first on the west coast and, more recently (in the 1990s), it was reported in Massachusetts on the east coast. Caterpillars of the winter moth defoliate trees in spring, and the flightless females emerge from pupae in the soil in late autumn or early winter to lay eggs that hatch just before bud burst, when they start feeding on fresh leaves.

Biological control programme

Six parasitoids were introduced to Nova Scotia from Europe in the 1950s. Two became established: a tachinid fly, Cyzenis albicans, and an ichneumonid wasp, Agrypon flaveolatum. Both species parasitize moth larvae and overwinter in pupa in the soil, but they have different roles in the moth’s population dynamics. Cyzenis albicans can reduce moth populations at outbreak densities, and A. flaveolatum probably plays a more important role at relatively low host densities. It has been shown that the establishment of the two parasitoids in eastern Canada favoured moth predation by some key local generalist predators that also help keep pest populations at low densities. Cyzenis albicans is specific to the winter moth, but there is uncertainty about the host range of A. flaveolatum, largely due to its uncertain taxonomic status.

After the success of the CBC programme in eastern Canada in the 1950s, the two parasitoids were released in western Canada (British Columbia) and western United States of America (Oregon) in the early 1980s, where they quickly became established, causing outbreaks to collapse. In Massachusetts, only C. albicans was released because it is highly specific to the winter moth (A. flaveolatum can also attack closely related moth species), and it has been established in that state since 2012.

Impact of classical biological control

The introduction of the two parasitoids to Canada is a classic case of successful CBC against a forest pest. The winter moth is now only a very minor pest in eastern Canada, where it causes less damage than in its area of origin. Populations of the moth also declined rapidly on the North American west coast following the establishment of C. albicans and A. flaveolatum, although, in some areas, densities are higher than in Nova Scotia. In Massachusetts, ongoing studies suggest that C. albicans alone will control the pest.

Key lessons

•Two natural enemies that play different roles in the population dynamics of a pest can be complementary in a CBC programme.

•Introduced natural enemies may enhance the effectiveness of native natural enemies on an invasive pest.

•Resolving the taxonomy of a natural enemy is essential for assessing its suitability as a potential BCA.

Further reading

Elkinton and Boettner (2014).

7.10 Ambermarked birch leaf miner in Canada and the United States of America

Insect pest: Profenusa thomsoni Konow (Hymenoptera: Tenthedinidae)

Native congeneric: Profenusa canadensis Marl. (Hymenoptera: Tenthedinidae)

Biological control agents: Lathrolestes thomsoni Reshchikov (Hymenoptera: Ichneumonidae); Aptesis segnis Provancher (Hymenoptera: Ichneumonidae); Lathrolestes soperi Reshchikov (Hymenoptera: Ichneumonidae)

Insect pest

The ambermarked birch leaf miner (Profenusa thomsoni) is a rare species in its native range of mainly peat bogs in central and northern Europe. Its larvae mine the leaves of birch trees (Betula spp.) but never cause significant damage. The species was introduced accidentally to North America at the beginning of the twentieth century, and it became a serious pest of birch in Alberta and the Northwest Territories, Canada, in the 1970s and in Alaska, United States of America, in the 1990s. Damage was particularly high in urban trees, with up to 90 percent of leaves damaged, severely affecting the aesthetic value of the trees.

Biological control programme

A CBC programme was initiated in the early 1990s to control P. thomsoni in Alberta. Surveys carried out in Europe found parasitoids that could potentially be introduced to Canada. In 1994, however, populations of P. thomsoni in Alberta crashed unexpectedly due to parasitism from a previously unknown ichneumonid wasp, Lathrolestes thomsoni (then designated as L. luteolator), an internal parasitoid of larvae in leaf miners.

L. thomsoni was also observed controlling the leaf miner in the Northwest Territories. It was introduced intentionally as a BCA in Alaska in 2004–2009 and became established at all release sites.

L. thomsoni has never been found on P. thomsoni in Europe, so it probably came from another host species in North America, although the possibility that it was introduced accidentally from Europe with its host, or from another region, cannot be ruled out. Interestingly, L. thomsoni was recently found parasitizing P. thomsoni in Massachusetts, United States of America, where the leaf miner has never occurred at outbreak densities since its arrival at the beginning of the twentieth century; it is possible that the parasitoid has been present in that region for a long time.

Impact of classical biological control

Populations of P. thomsoni in Alberta crashed within two years of the arrival of L. thomsoni and have remained low since. Damage levels also decreased significantly in Alaska, although in that region the decline of P. thomsoni was also attributed at least partly to two other ichneumonid parasitoids, Aptesis segnis and L. soperi. A. segnis is a native ectoparasitoid, attacking last instar host larvae in their earthen cells in soils – this species is also known from a native congeneric leaf miner, Profenusa canadensis. L. soperi is a larval endoparasite which, like L. thomsoni, is of unknown origin and has never been found on another host.

Key lesson

Invasive insects can be accidentally controlled by native natural enemies that attack the invader and by non-native natural enemies that arrive unintentionally.

Further reading

Digweed et al. (2003); Soper, MacQuarrie and Van Driesche (2015).

7.11 Fall webworm in China

Insect pest: Hyphantria cunea Drury (Lepidoptera: Arctiidae)

Biological control agent: Chouioia cunea Yang (Hymenoptera: Eulophidae)

Insect pest

The fall webworm (Hyphantria cunea), a native of North America, is an invasive forest insect pest in China. It was discovered there in 1979 in Dandong, a town in Liaoning Province on the border with the Democratic People’s Republic of Korea. The fall webworm has since spread to many other parts of China, including the provinces of Anhui, Hebei, Shaanxi and Shandong and the municipalities of Beijing and Tianjin.

The fall webworm defoliates many species of ornamental, forest and fruit trees as well as agricultural crops (it is known to use 175 plant species as hosts in 49 families and 108 genera). Initially, pesticides were applied in an attempt to control the species; due to the side-effects of pesticide use, however, biological control was explored in conjunction with other measures as a sustainable alternative for containing further spread and damage.

Biological control programme

A search was conducted in China for effective native insect natural enemies of the fall webworm; previous attempts to control the species in Europe using insect parasitoids introduced from North America had only limited success. Surveys conducted in the early 1980s in Shaanxi Province discovered potential native predators and parasitoids. Subsequent surveys in 1996–2000 throughout the range of the fall webworm in China resulted in the identification of 27 potential insect predators and parasitoids. Among these, an endoparasitic chalcid wasp, Chouioia cunea, which parasitizes the pupae of the fall webworm, was identified as an effective BCA. A mass-rearing and augmentative release programme was developed for the chalcid wasp using an alternative host, Antheraea pernyi.

Impact of classical biological control

Chouioia cunea has been deployed widely as an effective BCA as part of an IPM approach for the fall webworm in China.

Further reading

Yang (1989); Yang (1990); Yang et al. (2008).

Glossary

The definitions provided in this glossary have been collected from publications and the Internet and edited for clarity; note that not all terms listed here are used in the main text of this publication. Although the definitions of terms used in forestry and many other technical fields are often highly variable, considerable effort has been made to find common understandings to reduce confusion. In forestry, FAO and the International Union of Forest Research Organizations have collaborated for many years on this issue, producing, for example, a glossary on forest genetic resources. FAO has also developed terms and definitions for its Global Forest Resources Assessments, taking into account the recommendations of experts in various fora. Except in a few instances, this glossary provides only one definition for each term (usually with the source of the definition indicated), but readers should be aware that other meanings may exist. Note that the ISPMs use the definitions specified in ISPM 5 exclusively. For the latest definitions of the International Plant Protection Convention (IPPC), please refer to its website (www.ippc.int). For the latest definitions of the IOBC, please refer to its website (www.iobc/global.org).

Annex: List of pests, biological control agents and tree hosts mentioned in the guide

References and further reading

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Plant Health Australia. 2017. PLANTPLAN: Australian Emergency Plant Pest Response Plan. Version 3.1. Canberra, Australia (available at www.planthealthaustralia.com.au/wp-content/uploads/2017/12/PLANTPLAN-30-November-2017.pdf).

Secretariat of the North American Plant Protection Organization. 2011. RSPM 22. Guidelines for construction and operation of a containment facility for insects and mites used as biological control agents. North American Plant Protection Organization (available at www.nappo.org/files/2514/3895/9309/RSPM_22-07-07-11-e.pdf).

Secretariat to the Convention on Biological Diversity. 2011. Nagoya Protocol on Access to Genetic Resources and the Fair and Equitable Sharing of Benefits Arising from their Utilization to the Convention on Biological Diversity. Montreal, Canada (available at www.cbd.int/abs/doc/protocol/nagoya-protocol-en.pdf).

Slippers, B., Hurley, B.P. & Wingfield, M.J. 2015. Sirex woodwasp: a model for evolving management paradigms of invasive forest pests. Annual Review of Entomology, 60: 601–619.

Smith, R.F. & Reynolds, H.T. 1966. Principles, definitions and scope of integrated pest control. Proceedings of the FAO Symposium on Integrated Pest Control, 1: 11–17.

Soliman, E.P., Wilcken, C.F., Pereira, J.M., Dias, T.K.R., Zaché, B., Dal Pogetto, M.H.F.A. & Barbosa, L.R. 2012. Biology of Thaumastocoris peregrinus in different Eucalyptus species and clones. Phytoparasitica, 40(3): 218–227. https://doi.org/10.1007/s12600-012-0226-4

Soper, S., MacQuarrie, C.J.K. & Van Driesche, R. 2015. Introduction, establishment, and impact of Lathrolestes thomsoni (Hymenoptera: Ichneumonidae) for biological control of the ambermarked birch leafminer, Profenusa thomsoni (Hymenoptera: Tenthredinidae), in Alaska. Biological Control, 83: 13–19.

Tadic, M. 1958. Biological control of fall webworm (Hyphantria cunea Dr.) in Europe. Proceedings of 10th International Congress of Entomology, pp. 855–858.

USDA. 2010. Containment guidelines for plant pathogenic bacteria. (Includes mycoplasmas, spiroplasmas). United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (available at www.aphis.usda.gov/plant_health/permits/downloads/bacteria_containment_guidelines.pdf).

USDA. 2017. Bacteria, fungi, nematodes, phytoplasmas and viruses. Import information. United States Department of Agriculture (USDA) (available at www.aphis.usda.gov/aphis/ourfocus/planthealth/import-information/permits/regulated-organism-and-soil-permits/sa_plant_pathogens/ct_plant_pathogens).

Van Driesche, R.G. & Bellows, Jr. T.S. 1996. Biological control. New York, USA, Chapman & Hall.

van Lenteren, J.C., ed. 2012. Internet book of biological control. Version 6, Spring 2012. International Organisation for Biological and Integrated Control (available at www.iobc-global.org/publications_iobc_internet_book_of_biological_control.html).

Wilcken, C.F., Soliman, E.P., Sá, L.A.N., Barbosa, L.R., Dias, T.K.R., Ferreira Filho, P.J. & Oliveira, R.J.R. 2010. Bronze bug Thaumastocoris peregrinus Carpintero & Dellapé (Hemiptera: Thaumastocoridae) on Eucalyptus in Brazil and its distribution. Journal of Plant Protection Research, 50(2): 184–188.

Yang, Zhong-qi. 1989. A new genus and species of Tetrastichinae (Hymenoptera: Eulophidae) parasitizing Hyphantria cunea in China. Entomotaxonomia, 11: 117–130.

Yang, Zhong-qi. 1990. An effective natural enemy of Hyphantria cunea, Chouioia cunea Yang. Forest Pest Diseases, 1990(2): 17.

Yang, Zhong-qi, Wang, Xiao-yi, Wei, Jian-rong, Wang, Chuan-zhen & Qiao, Xiu-rong. 2008. Survey of the native insect natural enemies of Hyphantria cunea Dury (Lepidoptera: Arctiidae) in China. Bulletin of Entomological Research, 98: 293–302.

Yang, Zhong-qi, Wei, Jian-rong & Wang, Xiao-yi. 2006. Mass rearing and augmentative releases of the native parasitoid Chouioia cunea (Hymenoptera: Eulophidae) for biological control of the introduced fall webworm Hyphantria cunea in China. BioControl, 51(4): 401–418.

Adopted ISPMs and approved specifications

ISPM 2. 2007. Framework for pest risk analysis. Rome, IPPC, FAO (available at www.ippc.int/static/media/files/publication/en/2016/01/ISPM_02_2007_En_2015-12-22_PostCPM10_InkAmReformatted.pdf).

ISPM 3. 2005. Guidelines for the export, shipment, import and release of biological control agents and other beneficial organisms. Rome, IPPC, FAO (available at www.ippc.int/static/media/files/publication/en/2016/01/ISPM_03_2005_En_2015-12-22_PostCPM10_InkAmReformatted.pdf).

ISPM 5. Glossary of phytosanitary terms. Rome, IPPC, FAO (available at www.fao.org/3/a-y4224e.pdf).

ISPM 6. 2018. Surveillance. Rome, IPPC, FAO (available at www.ippc.int/static/media/files/publication/en/2018/06/ISPM_06_2018_En_Surveillance_2018-05-20_PostCPM13_KmRiysX.pdf).

ISPM 9. 2016. Guidelines for pest eradication programmes. Rome, IPPC, FAO (available at www.ippc.int/static/media/files/publication/en/2016/01/ISPM_09_1998_En_2015-12-22_PostCPM10_InkAmReformatted.pdf).

ISPM 11. 2017. Pest risk analysis for quarantine pests. Rome, IPPC, FAO (available at www.fao.org/3/a-j1302e.pdf).

ISPM 15. 2018. Regulation of wood packaging material in international trade. Rome, IPPC, FAO (available at www.fao.org/3/a-mb160e.pdf).

ISPM 17. 2017. Pest reporting. Rome, IPPC, FAO (available at www.fao.org/3/a-y4224e.pdf).

ISPM 21. 2004. Pest risk analysis for regulated non-quarantine pests. International Standard for Phytosanitary Measures No. 21. Rome, IPPC, FAO (available at www.fao.org/3/y5722e00.htm).

[1] Note that it is usually easier to calculate the economic benefits of CBC for agricultural pests than for forestry pests, partly because measuring differences in tree growth rates or timber production over relatively long rotations requires considerably more investment and time compared with measuring the growth of annual agricultural crops or the loss of fruit production.

[2] “Forestry Images” is an image database for forestry species of economic concern maintained by the Centre for Invasive Species and Ecosystem Health at the University of Georgia, United States of America; it is available at www.forestryimages.org. “PaDIL” – the Pest and Diseases Image Library – is an image database and information tool for biosecurity and biodiversity maintained by the Australian Government’s Department of Agriculture and Water Resources; it is available at www.padil.gov.au.

[3] “PestNet” is an email network to provide rapid advice and information on crop protection, including the identification and management of plant pests; it is available at www.pestnet.org.

[4] The list is available at www.fao.org/agriculture/crops/thematic-sitemap/theme/pests/jmps/ps-new

[5] Pherobase is available at www.pherobase.com

FAO Forestry Papers

1Forest utilization contracts on public Land, 1977 (E F S)

2Planning forest roads and harvesting systems, 1977 (E F S)

3World list of forestry schools, 1977 (E F S)

3 Rev.1World list of forestry schools, 1981 (E F S)

3 Rev.2World list of forestry schools, 1986 (E F S)

4/1World pulp and paper demand, supply and trade – Vol. 1, 1977 (E F S)

4/2World pulp and paper demand, supply and trade – Vol. 2, 1977 (E F S)

5The marketing of tropical wood in South America, 1976 (E S)

6National parks planning, 1976 (E F S)

7Forestry for local community development, 1978 (ar E F S)

8Establishment techniques for forest plantations, 1978 (Ar C E * F S)

9Wood chips – production, handling, transport, 1976 (C E S)

10/1Assessment of logging costs from forest inventories in the tropics – 1. Principles and methodology, 1978 (E F S)

10/2Assessment of logging costs from forest inventories in the tropics – 2. Data collection and calculations, 1978 (E F S)

11Savanna afforestation in Africa, 1977 (E F)

12China: forestry support for agriculture, 1978 (E)

13Forest products prices 1960–1977, 1979 (E F S)

14Mountain forest roads and harvesting, 1979 (E)

14 Rev.1Logging and transport in steep terrain, 1985 (e)

15AGRIS forestry – world catalogue of information and documentation services, 1979 (E F S)

16China: integrated wood processing industries, 1979 (E F S)

17Economic analysis of forestry projects, 1979 (E F S)

17 sup.1Economic analysis of forestry projects: case studies, 1979 (E S)

17 Sup.2Economic analysis of forestry projects: readings, 1980 (C E)

18Forest products prices 1960–1978, 1980 (E F S)

19/1Pulping and paper-making properties of fast-growing plantation wood species – Vol. 1, 1980 (E)

19/2Pulping and paper-making properties of fast-growing plantation wood species – Vol. 2, 1980 (E)

20Forest tree improvement, 1985 (C E F S) 20/2 A guide to forest seed handling, 1985 (E S)

21Impact on soils of fast-growing species in lowland humid tropics, 1980 (E F S)

22/1Forest volume estimation and yield prediction – Vol. 1. Volume estimation, 1980 (C E F S)

22/2Forest volume estimation and yield prediction – Vol. 2. Yield prediction, 1980 (C E F S)

23Forest products prices 1961–1980, 1981 (E F S)

24Cable logging systems, 1981 (C E)

25Public forestry administrations in Latin America, 1981 (e)

26Forestry and rural development, 1981 (E F S)

27Manual of forest inventory, 1981 (E F)

28Small and medium sawmills in developing countries, 1981 (E S)

29World forest products, demand and supply 1990 and 2000, 1982 (E F S)

30Tropical forest resources, 1982 (E F S)

31Appropriate technology in forestry, 1982 (E)

32Classification and definitions of forest products, 1982 (Ar E F S)

33Logging of mountain forests, 1982 (E F S)

34Fruit-bearing forest trees, 1982 (E F S)

35Forestry in China, 1982 (C E)

36Basic technology in forest operations, 1982 (E F S)

37Conservation and development of Tropical forest resources, 1982 (E F S)

38Forest products prices 1962–1981, 1982 (E/F/S)

39Frame saw manual, 1982 (E)

40Circular saw manual, 1983 (E)

41Simple technologies for charcoal making, 1983 (E F S)

42Fuelwood supplies in the developing countries, 1983 (Ar E F S)

43Forest revenue systems in developing countries, 1983 (E F S)

44/1Food and fruit-bearing forest species – 1. Examples from eastern Africa, 1983 (E F S)

44/2Food and fruit-bearing forest species – 2. Examples from southeastern Asia, 1984 (E F S)

44/3Food and fruit-bearing forest species – 3. Examples from Latin America, 1986 (E S)

45Establishing pulp and paper mills, 1983 (E)

46Forest products prices 1963–1982, 1983 (E/F/S)

47Technical forestry education – design and implementation, 1984 (E F S)

48Land evaluation for forestry, 1984 (C E F S)

49Wood extraction with oxen and agricultural tractors, 1986 (E F S)

50Changes in shifting cultivation in Africa, 1984 (E F)

50/1Changes in shifting cultivation in Africa – seven case-studies, 1985 (E)

51/1Studies on the volume and yield of tropical forest stands – 1. Dry forest formations, 1989 (E F)

52/1Cost estimating in sawmilling industries: guidelines, 1984 (E)

52/2Field manual on cost estimation in sawmilling industries, 1985 (E)

53Intensive multiple-use forest management in Kerala, 1984 (E F S)

54Planificación del desarrollo forestal, 1984 (S)

55Intensive multiple-use forest management in the tropics, 1985 (E F S)

56Breeding poplars for disease resistance, 1985 (E)

57Coconut wood – Processing and use, 1985 (E S)

58Sawdoctoring manual, 1985 (E S)

59The ecological effects of eucalyptus, 1985 (C E F S)

60Monitoring and evaluation of participatory forestry projects, 1985 (E F S)

61Forest products prices 1965-1984, 1985 (E F S)

62World list of institutions engaged in forestry and forest products research, 1985 (E F S)

63Industrial charcoal making, 1985 (E)

64Tree growing by rural people, 1985 (Ar E F S)

65Forest legislation in selected African countries, 1986 (E F)

66Forestry extension organization, 1986 (C E S)

67Some medicinal forest plants of Africa and Latin America, 1986 (E)

68Appropriate forest industries, 1986 (E)

69Management of forest industries, 1986 (E)

70Wildland fire management terminology, 1986 (E F S)

71World compendium of forestry and forest products research institutions, 1986 (E F S)

72Wood gas as engine fuel, 1986 (E S)

73Forest products: world outlook projections 1985–2000, 1986 (E F S)

74Guidelines for forestry information processing, 1986 (E)

75Monitoring and evaluation of social forestry in India – an operational guide, 1986 (E)

76Wood preservation manual, 1986 (E)

77Databook on endangered tree and shrub species and provenances, 1986 (E)

78Appropriate wood harvesting in plantation forests, 1987 (E)

79Small-scale forest-based processing enterprises, 1987 (E F S)

80Forestry extension methods, 1987 (E)

81Guidelines for forest policy formulation, 1987 (C E)

82Forest products prices 1967–1986, 1988 (E F S)

83Trade in forest products: a study of the barriers faced by the developing countries, 1988 (E)

84Forest products: World outlook projections – Product and country tables 1987–2000, 1988 (E F S)

85Forestry extension curricula, 1988 (E F S)

86Forestry policies in Europe, 1988 (E)

87Small-scale harvesting operations of wood and non-wood forest products involving rural people, 1988 (E F S)

88Management of tropical moist forests in Africa, 1989 (E F P)

89Review of forest management systems of tropical Asia, 1989 (E)

90Forestry and food security, 1989 (Ar E S)

91Design manual on basic wood harvesting technology, 1989 (E F S) (Published only as FAO Training Series, No. 18)

92Forestry policies in Europe – An analysis, 1989 (E)

93Energy conservation in the mechanical forest industries, 1990 (E S)

94Manual on sawmill operational maintenance, 1990 (E)

95Forest products prices 1969–1988, 1990 (E F S)

96Planning and managing forestry research: guidelines for managers, 1990 (E)

97Non-wood forest products: the way ahead, 1991 (E S)

98Timber plantations in the humid tropics of Africa, 1993 (E F)

99Cost control in forest harvesting and road construction, 1992 (E)

100Introduction to ergonomics in forestry in developing countries, 1992 (E F I)

101Management and conservation of closed forests in tropical America, 1993 (E F P S)

102Research management in forestry, 1992 (E F S)

103Mixed and pure forest plantations in the tropics and subtropics, 1992 (E F S)

104Forest products prices 1971–1990, 1992 (E F S)

105Compendium of pulp and paper training and research institutions, 1992 (E)

106Economic assessment of forestry project impacts, 1992 (E F)

107Conservation of genetic resources in tropical forest management – Principles and concepts, 1993 (E F S)

108A decade of wood energy activities within the Nairobi Programme of Action, 1993 (E)

109Directory of forestry research organizations, 1993 (E)

110Proceedings of the Meeting of Experts on Forestry Research, 1993 (E F S)

111Forestry policies in the Near East region – analysis and synthesis, 1993 (E)

112Forest resources assessment 1990 – tropical countries, 1993 (E)

113Ex situ storage of seeds, pollen and in vitro cultures of perennial woody plant species, 1993 (E)

114Assessing forestry project impacts: issues and strategies, 1993 (E F S)

115Forestry policies of selected countries in Asia and the Pacific, 1993 (E)

116Les panneaux à base de bois, 1993 (F)

117Mangrove forest management guidelines, 1994 (E)

118Biotechnology in forest tree improvement, 1994 (E)

119Numéro non assigné

120Decline and dieback of trees and forests – a global overview, 1994 (E)

121Ecology and rural education – Manual for rural teachers, 1995 (E S)

122Readings in sustainable forest management, 1994 (E F S)

123Forestry education – New trends and prospects, 1994 (E F S)

124Forest resources assessment 1990 – Global synthesis, 1995 (E F S)

125Forest products prices 1973–1992, 1995 (E F S)

126Climate change, forests and forest management – An overview, 1995 (E F S)

127Valuing forests: context, issues and guidelines, 1995 (E F S)

128Forest resources assessment 1990 – Tropical forest plantation resources, 1995 (E)

129Environmental impact assessment and environmental auditing in the pulp and paper industry, 1996 (E)

130Forest resources assessment 1990 – Survey of tropical forest cover and study of change processes, 1996 (E)

131Ecología y enseñanza rural – Nociones ambientales básicas para profesores rurales y extensionistas, 1996 (S)

132Forestry policies of selected countries in Africa, 1996 (E F)

133Forest codes of practice – Contributing to environmentally sound forest operations, 1996 (E)

134Estimating biomass and biomass change of tropical forests – A primer, 1997 (E)

135Guidelines for the management of tropical forests – 1. The production of wood, 1998 (E S)

136Managing forests as common property, 1998 (E)

137/1Forestry policies in the Caribbean – Volume 1: Proceedings of the expert consultation, 1998 (E)

137/2Forestry policies in the Caribbean – Volume 2: Reports of 28 selected countries and territories, 1998 (E)

138FAO Meeting on Public Policies Affecting Forest Fires, 2001 (E F S)

139Governance principles for concessions and contacts in public forests, 2003 (E F S)

140Global Forest Resources Assessment 2000 – Main report, 2002 (E F S)

141Forestry Outlook Study for Africa – Regional report: opportunities and challenges towards 2020, 2003 (Ar E F)

142Cross-sectoral policy impacts between forestry and other sectors, 2003 (E F S)

143Sustainable management of tropical forests in Central Africa – In search of excellence, 2003 (E F)

144Climate change and the forest sector – Possible national and subnational legislation, 2004 (E)

145Best practices for improving law compliance in the forest sector, 2005 (E F R S)

146Microfinance and forest-based smallscale enterprises, 2005 (Ar E F S)

147Global Forest Resources Assessment 2005 – Progress towards sustainable forest management, 2006 (E F S)

148Tendencias y perspectivas del sector forestal en América Latina y el Caribe, 2006 (S)

149Better forestry, less poverty – a practitioner’s guide, 2006 (Ar E F S)

150The new generation of watershed management programmes and projects, 2006 (E F S)

151Fire management – Global assessment 2006, 2007 (E)

152People, forests and trees in West and Central Asia – Outlook for 2020, 2007 (Ar E R)

153The world’s mangroves 1980–2005, 2007 (E)

154Forests and energy – Key issues, 2008 (Ar C E F R S)

155Forests and water, 2008 (E F S)

156Global review of forest pests and diseases, 2009 (E)

157Human-wildlife conflict in Africa – Causes, consequences and management strategies, 2009 (E F)

158Fighting sand encroachment – Lessons from Mauritania, 2010 (E F)

159Impact of the global forest industry on atmospheric greenhouse gases, 2010 (E)

160Criteria and indicators for sustainable woodfuels, 2010 (E)

161Developing effective forest policy – A guide, 2010 (E F S)

162What woodfuels can do to mitigate climate change, 2010 (E)

163Global Forest Resources Assessment 2010 – Main report (Ar C E F R S)

164Guide to implementation of phytosanitary standards in forestry, 2011 (C E F R)

165Reforming forest tenure – Issues, principles and process, 2011 (E S)

166Community-based fire management – a review (E)

167Wildlife in a changing climate (E)

168Soil carbon monitoring using surveys and modelling – (E)

169Global forest land-use change 1990–2005 (E F S)

170Sustainable management of Pinus radiata plantations (E)

171Edible insects – Future prospects for food and feed security (E F)

172Climate change guidelines for forest managers (E F S)

173Multiple-use forest management in the humid tropics (E S)

174Towards effective national forest funds, 2015 (E)

175Global guidelines for the restoration of degraded forests and landscapes in drylands – Building resilience and benefiting livelihoods, 2015 (E)

176Forty years of community-based forestry – A review of its extent and effectiveness, 2016 (E)

177Forestry for a low-carbon future – Integrating forests and wood products in climate change strategies, 2016 (E)

178Guidelines on urban and peri-urban forestry, 2016 (E)

179National socioeconomic surveys in forestry – Guidance and survey modules for measuring the multiple roles of forests in household welfare and livelihoods, 2016 (E F S)

180Making forest concessions in the tropics work to achieve the 2030 Agenda: Voluntary Guidelines, 2018 (E)

181Climate change for forest policy-makers – An approach for integrating climate change into national forest policy in support of sustainable forest management – Version 2.0, 2018 (E)

Ar – Arabic

C – Chinese

E – English

I – Italian

F – French

K – Korean

P – Portuguese

S – Spanish

R – Russian

M – Multilingual

* – Out of print

FAO Forestry Papers are available through the authorized FAO Sales agents or directly from Sales and Marketing Group, FAO, Viale delle Terme di Caracalla, 00153 Rome, Italy, or at www.fao.org/forestry/58718/en/