Abstract
A mutant form of E4, the enzyme responsible for insecticide resistance in M. persicae, was identified in a holocyclic population of aphids from peaches in Italy. The enzyme, FE4, differed from E4 electrophoretically, and also hydrolysed naphth-1-yl acetate, trans-permethrin and organophosphorus insecticides (but not methyl carbamates or dimethyl carbamates) slightly faster. Assaying the esterase with naphth-1-yl acetate therefore over-estimates the molar amount of enzyme present in comparison with such assays on E4, but since organophosphorus insecticides are hydrolysed at comparably increased rates, esterase determinations reliably indicate resistance to this class. On the other hand, resistance to carbamates depends mainly on sequestration of the insecticide by the enzyme, so that esterase assays over-estimate resistance to carbamates in aphids with FE4.
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