Electrophoretic Esterase Patterns in Insecticide-Resistant and Susceptible Mosquitoes1

The esterase patterns of insecticide-resistant and susceptible strains of Culex pipiens fatigans Wiedemann, Culex pipiens pipiens L., C. tarsalis Coquillett, and Anopheles albimanus Wiedemann, were investigated by starch gel electrophoresis. At least one highly active esterase is present in every organophosphate-resistant Strain of Culex spp. A highly active esterase B2, catalyzing the hydrolysis of β-naphthylacetate and being suppressible by DEF® (S,S,S-tributyl phosphorotrithioate) is most probably associated with organophosphorus multiresistance in C. p. fatigans from California, Esterase B2 has no equivalent in chlorpyrifos-resistant C. p. pipiens from France. Interspecific and interstrain differences in esterase patterns and their relationship to resistance are discussed.