Metabolism and excretion of the furanocoumarin xanthotoxin by parsnip webworm,Depressaria pastinacella

The parsnip webworm,Depressaria pastinacella, feeds on plants containing high concentrations of furanocoumarins. compounds toxic to many organisms. Parsnip webworm larvae were fed radiolabeled xanthotoxin to quantify the detoxification of this furanocoumarin. They metabolized approximately 95% of the ingested xanthotoxin, indicating that metabolic detoxification is important in their tolerance to this allelochemical. Excretion of xanthotoxin and its metabolites was not restricted to the frass but also occurred by means of the silk glands. The silk glands contained half as much of the tritiated compounds as the rest of the body. Because of the feeding habits of this insect, such an excretory pathway may have implications for interactions with predators and pathogens.