DOMINANCE OF INSECTICIDE RESISTANCE PRESENTS A PLASTIC RESPONSE

Dominance level of insecticide resistance provided by one major gene ( an insensitive acetylcholinesterase) in the mosquito Culex pipiens was studied in two distinct environments. Dominance level was found to be very different between environments, varying from almost complete dom inance to almost recessive when either propoxur (a carbamate insectici de) or chlorpyrifos (an orpanophosphorus insecticide) was used. To bet ter understand this plastic response, three environmental parameters w ere manipulated and their interactions studied. For chlorpyrifos, each parameter had a small effect, but when all parameters were changed, t he dominance level was greatly affected. For propoxur, one environment al parameter had a large effect by itself. It was further studied to u nderstand the causal relationship of this plasticity. Recessivity of r esistance was associated with more demanding environments. These resul ts are discussed in the context of the various theories of the evoluti on of dominance. It appears that dominance of insecticide resistance c annot be directly predicted by Wright's physiological theory.