Diagnostic esterases and insecticide resistance in the tobacco aphid, Myzus nicotianae Blackman (Homoptera: Aphididae)

Abstract

Insecticide resistance in the tobacco aphid, Myzus nicotianae Blackman, from different localities in the southeastern United States has been found to exist mainly in aphids with red body coloration. Frequency distribution of esterase activity in individual tobacco aphids collected from a tobacco field and a greenhouse indicated that organophosphate resistance was always linked to high carboxylesterase activity toward 1-naphthyl acetate. Two approaches were taken to speed up the detection methodology of the frequency of resistant phenotypes. First, an abbreviated bioassay test, using malathion as a reporter molecule, was developed to rapidly distinguish between OP-resistant and susceptible phenotypes of the tobacco aphid. A time threshold of 50 min following aphid exposure to 50 ppm malathion in a water suspension accurately discriminated between susceptible and resistant phenotypes. Second, assays of aphid carboxylesterases, using the acetates and propionates of 1-naphthol, 2-naphthol, and 4-nitrophenol, were performed to optimize and better understand the esterase discriminating activity between resistant and susceptible phenotypes. Only activity toward 1-naphtholic esters unambiguously discriminated between susceptible and resistant aphids. In general, resistance to malathion appeared to be esterase-mediated and some electrofocusing-detectable esterase isozymes were associated with resistance.