Some organophosphate insecticides were less toxic to male Oriental fruit moths (OFM) than to females in in vivo toxicity assays. The moths were from a laboratory population started from larvae collected from a research farm in New Jersey, with the history of organophosphate insecticide use. Higher tolerance to organophosphates in these males may be attributed to the gender differences in the target site, acetylcholinesterase, and also to differences in detoxifying enzymes, such as the general esterases. Male moths showed significantly higher general esterase activity than females in both soluble and membrane-bound fractions. Among heads, thoraxes, and abdomens, the largest difference between males and females was in the abdomens. Among tissues, the fat body/hemolymph fraction had the highest activity. A population of moths that was never exposed to insecticides showed the same gender difference in esterase activity, although to a lesser degree. This suggests that the difference in esterase activity between male and female moths is an inherent characteristic of the OFM species and unrelated to insecticide resistance, and that selection pressure by organophosphate insecticides can amplify the difference.
Species 1: Lepidoptera Tortricidae Grapholita molesta (oriental fruit moth)
Keywords: organophosphate, tolerance
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