Topic: The Ecology and Life-Cycle of the GGB
Duration: 1 hour 45 minutes
Objectives:
At the end of this session, the participants should be able to know:
i) The environment in which the GGB thrives.
ii) The life-cycle of the GGB.
Target Group:
- Subject Matter Specialists (SMS's)
- Technical Assistants (TA's)
- Farmers
- Local leaders
Training Materials:
i) Samples of materials which have been attacked by the GGB, i.e.- maize grains
- maize cobs
- dried cassava
- timber/wood
- sisal jute) baskets/bagsii) Magnifying glasses (lenses)
iii) Wall chart of the life cycle of the GGB - complete metamorphoses
iv) BB with chalk sticks or FC with paper and felt pen.
Process:
30 minutes
a) The trainer should pass around the well-labelled samples of the materials (see list above) which have been attacked by the GGB. Each participant should be allowed at least a minute or two to examine each sample before passing it on to the neighbouring participant. Participants should be encouraged to identify:- presence of adult GGB beetles, larvae and pupae;
- presence of bores/perforations/holes made by the GGB.b) The trainer should explain that the GGB is capable of living in many items.
30 minutes
c) The following facts of the ecology of the GGB should then be taught:i) It has been observed that the GGB can bore and live in wood.ii) The beetle can feed on dried cassava and some varieties of wheat and sorghum.
iii) The GGB feeds and breeds on maize.
iv) The beetle is capable of feeding on whole grains by tunnels (holes), generating large quantities of dust.
v) The GGB feeds on the most nutritious part of the maize kernel, i.e. the endosperm. Thus, the remaining dust and pieces of maize have almost no food value to the human being.
vi) Observations have shown that GGB causes more damage to stored cob maize than shelled grains. It multiplies faster on cob maize.
vii) The GGB can subsist very comfortably at temperatures ranging from 22° to 35°C and relative humidities of between 50 and 80% (most places in Kenya fall within the above ranges). So, the GGB can survive very well almost anywhere in Kenya.
d) The trainer should, at this stage, summarize the ecology of the GGB, i.e. points i) to vii) above before proceeding to the life-cycle.
30 minutes
e) The life-cycle of the GGB should be explained with the aid of the wall chart. The following facts should be taught:1) The female GGB lays between fifty and six hundred eggs, either singly or in pockets of about twenty eggs in the maize kernels. The eggs are laid in cavities dug at right angles to the main tunnels made by the GGB. The number of eggs laid depends on tempera ture and food availability,2) The eggs hatch into larvae, the larvae develop into pupae and the pupae later develop into beetles. The survival rate and the period it takes to complete the cycle depends on the availability of food (maize starch), temperature and relative humidity conditions:
i) Under optimal conditions (32°C and 80% r.h.), eggs develop into adults within 27 days.ii) Under unfavourable conditions (18°C and 60% r.h.), eggs develop into adults within 166 days.
3) The adult male lives for about 45 days while the adult female lives for about 61 days. The female becomes sexually mature, i.e. starts laying eggs after five to ten days.
4) Both the adult beetles and larvae feed on maize.
15 minutes
f) The trainer should allow question time after which he/she should summarize the lesson by briefly mentioning:i) the ecology and favourable conditions for the multiplication of the GGB;
ii) the stages of the life-cycle of the GGB;
iii) the time to maturity and the life expectancy of the GGB.5) lender optimal conditions, the stages of development from egg to adult take about twenty seven days. Both the adult GGB and the larvae feed on maize.
