CONICET | Buscador de Institutos y Recursos Humanos

The organophosphorus azinphosmethyl (AzMe) is extensively applied in northern Patagonia (South Argentina) to manage codling moths (Cydia pomonella). This area is irrigated by fast-flowing channels providing a favorable habitat for many species including amphipods (Hyalella curvispina) and a field-mixed population of black flies (Simulium bonaerense, Simulium wolffhuegeli, and Simulium nigristrigatum). In the present study, AzMe susceptibility and carboxylesterase (CarbE) activity from both insecticide-exposed and nonexposed field populations were studied. The median lethal dose (LD50) determined in codling moths from an insecticide-treated orchard was significantly higher (3.48 µg/insect) than that observed in those from an untreated orchard (0.69 µg/insect). Similarly, the median lethal concentration (LC50) determined in black flies collected from the treated area (0.021 mg/L) was significantly higher than that recorded in those from the untreated site (0.011 mg/L). For amphipods, both a subpopulation susceptible to AzMe (LC50 = 1.83 µg/L) and a resistant one (LC50 = 390 µg/L) were found in the treated area. Both subpopulations were more resistant to AzMe than the one from the untreated site (LC50 = 0.43 µg/L). Significant differences (p < 0.001) in CarbE activities were observed between populations from pesticide-treated and untreated areas. Mean activities from treated and untreated sites were 0.21 ± 0.16 and 0.016 ± 0.008 µmol/min/mg protein for codling moths; 2.17 ± 1.71 and 0.81 ± 0.35 µmol/min/mg protein for black flies and 0.27 ± 0.10 and 0.14 ± 0.07 µmol/min/mg protein for amphipods, respectively. The results suggest that enhanced CarbE activity is one of the mechanisms that provide AzMe resistance in H. curvispina, Simulium spp. and C. pomonella populations from the insecticide-treated areas.

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