Chemical ecology and integrated management of the banana weevil Cosmopolites sordidus in Uganda

Infochemicals (pheromones and kairomones) maypotentially be used for control of the banana weevil Cosmopolites sordidus (Germar)(Coleoptera: Curculionidae).Cosmopolitessordidus is a major pest of East African highland banana and plantains in most banana growing regions of the world. The weevil produces an aggregation pheromone that attracts both males and females. The attractive isomer sordidin has been identified and synthesized, and is commercially available.The objective of the research project described in this thesis was to investigate whether an infochemical-based trapping system can be used to control C. sordidus under Ugandan conditions. In laboratory and field experiments, C. sordidus responded in an additive way to the combination of the fermented plant tissue and the aggregation pheromone. The effect was, however, more pronounced in laboratory than field experiments. Several factors such as thepest biology,pheromone efficacy, trap parameters, cropping system and environmental factors were found to variously influence the effectiveness of the pheromone-baited traps. The effectsof doubling pheromone trap densities from 4 to 8 per ha on C. sordidus population density and plant damage were negligible in an on-farm experiment . The pheromone-trapping system on farmers' fields was therefore not effective at the trap density recommended by the supplier (4 traps per ha).Olfactory responses of the banana weevil predatorsDactylosternumabdominale (Coleoptera: Hydrophilidae) and Pheidole megacephala (Hymenoptera: Formicidae)towards volatiles from banana pseudostem tissue (kairomones) and the synthetic banana weevil pheromone were evaluated in a two-choice olfactometer. Both predators discriminated between fermenting banana pseudostem tissue and clean air.There was no evidence that the pheromone influences predator distribution around the trap in the field.In experiments to investigate whether pheromone trapping can be integrated with use of entomopathogenic fungi, Beauveria bassiana to control C. sordidus,we observed that weevils can be aggregated on banana mats on which pheromone-baited traps are placed and on adjacent mats.Infected weevils were also observed to transmit the fungal pathogen to healthy individuals in the field. Weevil mortality due to pathogen infection was significantly higher in plots where aggregation pheromone was used in combination with B. bassiana compared to when the pathogen was applied without the pheromone. The data demonstrate that the banana weevil aggregation pheromone could be used to enhance the dissemination of B. bassiana for the control of C. sordidus.This project provides experimental evidence to further develop the application of the synthetic aggregation pheromone to control C. sordidus in Ugandan banana production by small scale farmers.The aggregation pheromone should be considered to be a good component of an IPM system in which it may not be effective by itself but stimulate several mortality factors for the control of the banana weevil. The next major strategy for use of pheromones is therefore to further exploit the potential to integrate entomopathogenic fungi and nematodes in the trapping system.