Aphid carboxylesterases: Biochemical aspects and importance in the diagnosis of insecticide resistance

Abstract

The activity of general carboxylesterases from susceptible and malathion-resistant strans of the green peach aphid, Myzus persicae, and the tobacco aphid, M. nicotianae, was examined using 10 1-naphtholic esters. The activity showed a parabolic relationship with the number of carbon atoms in the substrate acyl moiety. The maximal activity was obtained with 1-naphthyl propionate and 1-naphthyl butyrate, respectively, for the above species. No interstrain differences in the general profile of the structure-activity relationship were observed. However, an elevated carboxylesterase activity in the resistant strains when compared to the reference-susceptible strain was observed with each of the tested substrates, and the bestowed activity correlated with the degree of malathion resistance. The zymograms and intensity of the carboxylesterase bands when resolved by wide range isoelectric focusing (pH 3.5–9.5) and stained with Fast Blue B salt using 1-naphthyl acetate, 1-naphthyl propionate, and 1-naphthyl caproate as substrates correlated favorably with the general activity. From the above results a filter paper esterase test was developed and used for the diagnosis of the level of resistance in individual aphids. This test showed an excellent agreement with the susceptibility bioassay test of malathion against the green peach aphid. However, the test did not make possible an unambiguous discrimination between susceptible and resistant tobacco aphids. The possible impact of this and other more specific tests on the management of aphid populations is discussed.