Defense of parsnip webworm against phototoxic furanocoumarins: Role of antioxidant enzymes.

The parsnip webworm,Depressaria pastinacella (Lepidoptera: Oecophoridae), feeds on plants rich in furanocoumarins, phototoxic allomones. Final-instar larvae possess high levels of activities of antioxidant enzymes (Superoxide dismutase, catalase, glutathione reductase), which detoxify oxygen radicals generated from the furanocoumarins of their host plants. When added to an artificial diet, three linear furanocoumarins (xanthotoxin, bergapten, imperatorin) do not increase levels of the antioxidant enzymes. However, on diets containing both xanthotoxin and piperonyl butoxide, a cytochrome P-450 inhibitor, food utilization indices of the insect are reduced and superoxide dismutase activity is enhanced. These data suggest that cytochrome P-450s act as a primary detoxification system of ingested furanocoumarin, and antioxidant enzymes as a backup system to detoxify oxygen radicals generated by unmetabolized furanocoumarins.