Resistance to insecticides in insect vectors of disease estα3, a novel amplified esterase associated with amplified estβ1 from insecticide resistant strains of the mosquito Culex quinquesfasciatus

Resistance to insecticides in insect vectors of disease: estα3, a novel amplified esterase associated with amplified estβ1 from insecticide resistant strains of the mosquito Culex quinquefasciatus. Experimental Parasitology 87, 253-259. Vector control programmes in many countries face the dual problems of parasite drug resistance and insecticide resistance in the insect vectors of the disease. Here we report for the first timea new esterase-based insecticide resistance mechanism in the filariasis vector Culex- quinque-fasciatus. The field collected COL strain of C. quinquefasciatus from Columbia was heterogeneous for organophosphurus insecticide resistance. On native polyacrylamide gels it had an elevated β-naphthyl acetate specific esterase with the same R(f) as that for the Estβ1s involved in insecticide resistance in other strains of this mosquito species. After five generations of temephos insecticide selection, both the esterase specific activity with p-nitrophenyl acetate and the temephos LC50 values were increased, suggesting that elevation of esterase activity was the underlying mechanism of resistance. Western blots with antisera raised to Estα2 and Estβ2 from C: quinquefasciatus indicated that the COL strain had an elevated Estα3 enzyme which co-migrated on native gels with Estβ1. Southern blots indicated that an estα3 gene was amplified in the COL strain and a Cuban mosquito strain (MRes), although the restriction digest patterns of the estβ1 genes in these two strains are different. In contrast, the Californian TEMR strain, with the amplified estβ1 gene, had no associated elevated Estα. Restriction digest patterns for COL and TEMR DNA suggest that they contain an identical Estβ1 gene, but our data suggest that the estα3 gene occurs on the same amnplicon as an estβ1 gene although the genes are probably >10 kb apart. Hence, either the COL strain has two estβ1 genes or the estβ1 amplicon in TEMR has been disrupted at some stage during the long colonisation of this strain and the amplified estα has been lost.