Definition: Manipulation of beneficial organisms with the goal of reducing pest populations on an economically acceptable level
Teretriosoma nigrescens (T.n.) as a biological control means to the GGB
Teretriosoma nigrescens
1) It lives in the same surroundings (maize, cassava, etc.) and climatic zones as the GGB.2) Its size is such that it can easily go through the pores or bores made in maize, cassava, wood, etc. by the GGB.
3) In order to penetrate the bore, it uses its relatively strong legs to sweep away the frass left in the passages by the GGB.
4) It is sensitive to the aggregation pheromone (smell sent out by the GGB beetle to attract other GGB's). So it is easy for it to locate the GGB wherever it may hide.
5) The T.n. beetle feeds on the eggs, larvae and pupae of the GGB. Each adult T.n. eats about one to 1.5 GGB larvae per day.
6) The T.n. larvae also feeds on GGB eggs, larvae and pupae. T.n.'s larvae are even more ferocious than the adult beetles, each larva of T.n. is capable of consuming about 4.5 GGB larvae per day.
7) In an experiment carried out to determine the effectiveness of T.n. to control the GGB biologically, the predator was introduced to loose white maize and to maize left on cobs. In each case, the same quantity of maize was left free to act as a control. The four quantities of maize were observed for a period of 110 days (nearly four months). The results are summarized in the following table:
|
|
Loose Maize |
Maize on Cobs |
|
Population of GGB present in maize where T.n. was NOT introduced |
640 |
1,109 |
|
Population of GGB present in maize where T.n. WAS introduced |
85 |
315 |
|
Relative reduction in population of GGB |
87% |
72% |
8) The same experiment showed that, in the case of loose maize, losses were reduced by 76% when T.n. was introduced. The corresponding reduction in losses for maize still on cobs was 63%.9) It can be shown that, up to a point, the higher the population of T.n. in the maize, the lower the losses that may be incurred by the farmer. However, after a certain optimum T.n. population level, no further effect may be observed due to shortage of food for T.n. and cannibalism which sets in.
