Fenitrothion-deltamethrin cross-resistance conferred by esterases in Guatemalan Anopheles albimanus

Abstract

Biochemical tests and bioassays show elevated nonspecific esterase activity to cause fenitrothion-deltamethrin cross-resistance in Guatemalan Anopheles albimanus adults and larvae. Resistance to both insecticides was nearly abolished by a specific esterase inhibitor (DEF). Polyacrylamide gel electrophoresis (PAGE) revealed an intensely staining esterase zone in all resistant mosquitoes, but in none of the susceptibles. All individuals surviving exposure to each of the two insecticides possessed this esterase zone. Mosquitoes with elevated esterase activity in microplate assays were those possessing the intensely staining zone. Isoelectric focusing electrophoresis resolved the zone into a series of bands, with elevated activity in resistant individuals. Densitometric measurements of the esterase zone on PAGE minigels suggest that elevated levels of these esterases may be the product of an amplified gene. The electrofocusing gels, chromatofocusing, and high-performance liquid chromatography allow estimates of nondenatured molecular weight (60,000) and p I (4.6). The resistance esterase activity shows some characteristics of B-esterases.