The influence of the host plants tobacco, chilli and brinjal on the susceptibility of Myzus persicae (Sulz.) to five OP insecticides was assessed. The order of toxicity of the insecticides to the aphids on tobacco was monocrotophos > demeton methyl > dimethoate > methamidophos > acephate, on chilli; methamidophos = monocrotophos > demeton methyl = acephate > dimethoate and on brinjal, methamidophos = monocrotophos > acephate > demeton methyl = dimethoate. Among the five insecticides, monocrotophos had the highest inhibitory potency in vitro as indicated by I50 and ka values, followed by demeton methyl, dimethoate, methamidophos and acephate. Electrophoretograms of homogenates of aphids adopted to chilli and brinjal showed a higher activity of the detoxicating enzyme carboxylesterase than found in aphids on tobacco.
