The effects of environmental conditions on tolerance to malathion in bruchid beetles (Coleoptera: Bruchidae)

Bruchid beetles are economically important pests of grain legumes. Their medium to high level infestation is being controlled with insecticide. This study investigated the effects of environmental factors such as temperature, toxicant concentration, food and bruchid geographical strain on malathion tolerance in Callosobruchus species (c. maculatus, C. chinensis and C. rhodesianus). There were variations in insecticide tolerance among the species and C. maculatus which is the most widely spread and known showed the highest tolerance. Geographical origin had a pronounced impact on the response of C. maculatus to malathion. There was a positive relationship between temperature effect and bruchid susceptibility to malathion as often observed with organophosphate. The impact of food on insecticide tolerance in Callosobruchus was quite unpredictable. Overall, the interactive effects of all the factors are very complex. An alteration of anyone factor could either enhance or reduce tolerance. This could be driven by bruchid ancestry or fitness cost. Biochemical pathway study with malaoxon (malathion metabolite) ruled out acetylcholinesterase (AChE) as primarily responsible for malathion tolerance in bruchids; though it could be an additional factor to other tolerance mechanisms. However, there was variation in AChE activity among the species and strains with influence from the rearing food. Preliminary screening of the bruchids for the endosymbiont Wolbachia, prior to studies on its effect on insecticide tolerance was undertaken. The study revealed a high probable presence of this organism in C. maculatus and C. rhodesianus, which were previously thought to be non-host species. The implication of these findings in order to optimize bruchid management especially with insecticides to avoid/combat the development of insecticide resistance is discussed. This includes the impacts on legume breeding, production, transportation and storage.EThOS - Electronic Theses Online ServiceGBUnited Kingdo