Qualitative differences between populations of culex quinquefasciatus in both the esterases a2 and b2 which are involved in insecticide resistance

Organophosphate resistance in Culex mosquitos is commonly due to elevation of esterase activity. The usual form of elevation involves esterases A2 and B2 which are always together in the same individual insect. Using previously established purification methods, the purified esterases A2 and B2 from three resistant strains of Culex quinquefasciatus have been isolated and characterized. Substrate kinetic studies as well as the kinetics of insecticide interaction demonstrate that the esterases A2 and B2 differ both from each other and in the forms found in the three strains. That variations exist in the esterases in several resistant strains indicates polymorphism in the mosquito enzymes. This finding supports the hypothesis of insecticide resistance occurring multiple times and selecting different resistance-conferring esterases.