Synergism Studies with Organophosphorus Resistant Strains of the Indianmeal Moth13

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Abstract
Larvae of the last instar of Plodia interpunctella (Hübner) from susceptible and multiple organophosphorus (OP) resistant strains (T and M) were pretreated with piperonyl but oxide (Pb) and S, S, S-tributyl phosphorothioate (DEF). Susceptibility of larvae to malathion, dichlorvos, pirimiphos methyl, diazinon, and fenitrothion was then determined. In addition, larvae from each strain were tested against fenitro-oxon after Pb treatment. Pb equally synergised the chemicals, except malathion; in addition, it increased toxicity of fenitro-oxon. This result indicates that mixed function oxidases have a significant role in resistance to dichlorvos, pirimiphos methyl, diazinon, and fenitrothion. DEF completely restored susceptibility of the OP resistant strains to the aforementioned OP insecticides. The data indicate that the DEF mode of action deals with blocking both esterases and oxidases.