Induction of detoxification enzymes in phytophagous insects: Role of insecticide synergists,larval age,and species

Five insecticide synergists, all of which were either methylenedioxyphenyl compounds or analogs, were compared as to their effect on cytochrome P450 monooxygenase induction caused by an allelochemical in fall armyworm larvae. Feeding the synergists (piperonyl butoxide, safrole, isosafrole, MGK 264, and myristicin) individually to the larvae caused decreases in the microsomal aldrin epoxidase activities ranging from 38% to 74% when compared with controls. Feeding indole-3-carbinol resulted in a 4-fold increase in the microsomal epoxidase activity. However, cotreatment of any of the synergists and the inducer completely eliminated the induction. Sixth instar larvae were more inducible than second instar larvae with respect to microsomal epoxidase and glutathione transferase in the fall armyworm. Enzyme inducibility varied widely among the seven phytophagous Lepidoptera examined. When indole-3-carbinol was used as an inducer of microsomal epoxidase, the extent of inducibility of the enzyme was fall armyworm > velvetbean caterpillar > corn earworm > beet armyworm > tobacco budworm > cabbage looper > diamondback moth. When indole-3-acetonitrile was used as an inducer, the inducibility of glutathione transferase was fall armyworm > beet armyworm > corn earworm > cabbage looper > velvetbean caterpillar > tobacco budworm > diamondback moth. Inducibility of five microsomal oxidase systems also varied considerably in the corn earworm, indicating the multiplicity of cytochrome P450 in this species. Microsomal epoxidase and glutathione transferase were induced by cruciferous host plants such as cabbage and their allelochemicals in diamondback moth larve. © 1993 Wiley-Liss, Inc.