Behavioral effects of carotenoid sequestration by the parsnip webworm, Depressaria pastinacella

The parsnip webworm, Depressaria pastinacella, acquires a distinct yellow stripe when it consumes the yellow flowers of its principal host plant, Pastinaca saliva, the wild parsnip. Caterpillars raised on artificial diet lacking host-plant material lack this yellow coloration. By chemical characterization and comparison of caterpillars raised on parsnip flowers and on artificial diet, we were able to determine that lutein, along with smaller amounts of other xanthophylls from the host plant, is selectively sequestered in the fat body. In bioassays designed to measure avoidance of ultraviolet light, caterpillars raised on parsnip flowers or on artificial diet supplemented with lutein were less likely to avoid exposure to ultraviolet light than caterpillars raised on unaugmented artificial diet and thus lacking sequestered carotenoids. The ability to sequester xanthophylls, which are highly effective antioxidants, may confer a selective advantage on these caterpillars, whose apiaceous host plants produce large quantities of furanocoumarins, natural products that are photoactivated by light wavelengths in the ultraviolet region; such sequestered pigments may reduce not only the oxidative stress associated with ultraviolet light and diurnal foraging but also the photooxidative stress associated with ingestion of photoactive furanocoumarins.