Differences in photoactivating light intensities and the sequestration of host plant lutein may alter the efficacy of phototoxins against insect herbivores. We examined lutein sequestration by the parsnip webworm Depressaria pastinacella (Lepidoptera: Elachistidae) from populations in western North America that experience different UV intensities, as well as phototoxic furanocoumarins in the host plants Heracleum lanatum and Pastinaca sativa. Total furanocoumarin and total linear furanocoumarin contents of fruits were negatively correlated with UV irradiance, whereas total angular furanocoumarin content was positively correlated with UV irradiance. Among the individual furanocoumarins, bergapten, and xanthotoxin were negatively correlated, sphondin was positively correlated, and angelicin, imperatorin, and isopimpinellin were not correlated with UV irradiance. In contrast to the variation in furanocoumarin content, midgut metabolism rates for five furanocoumarins did not differ significantly among populations from New Mexico to Alberta. All five populations displayed metabolism rates near reported maximum values, suggesting that these webworms metabolize furanocoumarins at the limits imposed by existing genetic variation. Although lutein content of fruits did not vary with UV irradiance, lutein sequestration by sixth instars was significantly correlated with UV irradiance. Webworms from montane populations experiencing high levels of UV irradiance may rely on the ameliorative value of lutein against furanocoumarin toxicity to complement limited cytochrome P450-mediated metabolism of furanocoumarins. Differences in UV light intensities, lutein sequestration, and the presence of the polyembryonic parasitoid Copidosoma sosares Walker (Hymenoptera: Encyrtidae) may all be factors that interfere with the furanocoumarin-mediated interaction between the parsnip webworm and its hosts in these western populations.
Species 1: Lepidoptera Elachistidae Depressaria pastinacella (parsnip webworm)
Species 2: Hymenoptera Encyrtidae Copidosoma sosares
Keywords: cytochrome P450, furanocoumarin
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