The 1-benzoyl-3-phenylurea insecticide diflubenzuron is a potent inhibitor for the conversion of (14)C-labeled glucose to (14)C-labeled chitin in isolated abdomens of newly emerged adult milkweed bugs (Oncopeltus fasciatus Dallas). The inhibitory activity of 24 diflubenzuron analogs in this in vitro chitin-synthesizing system is in good agreement with their toxicity to fifth instar nymphs of this species. These insecticides act quickly and directly within the integument to ultimately block the terminal polymerization step in chitin formation.
The flavin adenine dinucleotide--dependent monooxygenase in mammalian hepatic microsomes plays a major role in the oxidative metabolism of thioether-containing pesticides. Thirty-four compounds were tested, and it was determined that organophosphorus insecticides such as disulfoton and phorate are rapidly oxidized by the purified enzyme to their corresponding sulfoxides. The enzyme does not catalyze the oxidation of the thiophosphoryl and thiol sulfur atoms of these or other phosphorothioates and phosphorodithioates, or the oxidation of the sulfoxide to the sulfone. Carbamates aldicarb and Croneton are also oxidized, but at a lower rate.
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