Natural enemies of Bathycoelia thalassina (Herrich-Shaeffer) (Hemiptera: Pentatomidae), a pest of cocoa in Ghana
(1) A large number of species of natural enemies were found associated with Bathycoelia thalassina. These comprised 15 insect, 5 spider and 3 vertebrate species. (2) Amongst the parasites, two species of Trissolcus (Hymenoptera: Scelionidae) were most commonly reared from the eggs of B. thalassina. Parasitization by these was about 10 percent in the field and nearly 80 percent in the insectary. (3) Methods were developed to mass rear Trissolcus spp. in the laboratory. The complete life cycle of the parasites was followed in the insectary. (4) The host finding and oviposition behaviour of Trissolcus spp. was studied in detail. The efficiency of the parasites was affected by the age and the fertility of the host eggs, but not by their own age, the surface area of the host eggs or the duration of the period over which the host eggs were exposed. There was no loss of efficiency over 12 generations in the insectary and the parasites could reproduce parthenogenetically. (5) The Trissolcus spp. were non-specific to B. thalassina eggs and would in the field parasitize other pentatomid eggs e.g. Nezara spp. and Bathycoelia rodhaini. (6) The low incidence of parasitization by Trissolcus spp. in the field as compared with the insectary was attributed to poor searching ability of the parasites in locating eggs. (7) Cylindromyia cribrata (Villen) (Tachinidae: Diptera) was found to parasitize the larvae and adults of B. thalassina. The parasitization was on average 40 percent in the insectary and 23 percent in the field. (8) The life cycle of C. cribrata was followed in the insectary and observations made on mating and oviposition behaviour. (9) It was found that not all adult B. thalassina parasitized by C. cribrata died. Crosses between parasitized and non-parasitized adults showed that the parasite had an adverse effect on the male host. Normal females fertilized by parasitized males did not lay any eggs. 4 percent of the parasitized females fertilized by normal males laid fertile eggs. The parasitization by C. cribrata was found to be density dependent, buy that by Trissolcus spp. appeared to be independent of host density. (10) Predation of B. thalassina eggs was about 20 percent in the field, mainly by ants and spiders. A mean larval predation of 31 percent was by spiders, ants, mantids and reduviids. (11) Field experiments showed that Gamma-BHC, the commonly used anti-capsid insecticide in Ghanaian cocoa-farms had an adverse effect on the natural enemies of B. thalassina. It was found that only 2 percent of the initial population of B. thalassina reached the adult stage when they were exposed to all possible natural enemies, but 71 percent reached adulthood when most of these enemies had been removed by spraying. It was concluded that the extensive use of lindane has encouraged an increase in B. thalassina population to pest level.
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| Format: | biblioteca |
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1976
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| Subjects: | THEOBROMA CACAO, BATHYCOELIA THALASSINA, INSECTOS DEPREDADORES DE LOS FRUTOS, ENEMIGOS NATURALES, MUESTREO, PARASITISMO, CICLO VITAL, INSECTICIDAS, EVOLUCION DE LA POBLACION, GHANA, |
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