| Insect herbivores that encounter phototoxic plant secondary compounds also consume antioxidants capable of reducing the efficacy of these chemicals. I investigated the effects of the xanthophyll lutein on the parsnip webworm, Depressaria pastinacella, and its interactions with host plant furanocoumarins activated by ultraviolet A light (UVA). Lutein ameliorates the negative effects of dietary xanthotoxin on neonate survivorship and sixth instar performance. Lutein reduced the toxic effects of xanthotoxin on sixth instar growth through post-ingestive effects on absorption and food conversion, rather than consumption. The absence of significant model interactions between UVA and diet components suggests that amelioration is not mediated by UVA.; Webworms can reduce phototoxicity through light avoidance. Sixth instars fed artificial diets supplemented with lutein, β-carotene, bixin, canthaxanthin, capsanthin, lycopene, or host plant material avoided UVA less often than webworms fed retinol or deprived of carotenoids.; Dietary lutein also affects xanthotoxin metabolism and cytochrome P450 enzyme expression. Sixth instars fed lutein showed higher metabolic rates than webworms reared on xanthotoxin-supplemented or unsupplemented diets. This enhancement of xanthotoxin metabolism may be due to upregulation of P450 enzymes, as shown by RT-PCR.; I examined lutein sequestration by sixth instars from populations in western North America that experience different UV intensities, as well as host plant furanocoumarins. Total furanocoumarins and total linear furanocoumarins were negatively correlated with UV irradiance (UVI), whereas total angular furanocoumarins were not correlated. Angelicin, bergapten, isopimpinellin, and xanthotoxin were negatively correlated, sphondin was positively correlated, and imperatorin was not correlated. Populations with the parasitoid Copidosoma sosares Walker (Hymenoptera: Encyrtidae) present had lower concentrations of total furanocoumarins, linear furanocoumarins, angelicin, bergapten, imperatorin, isopimpinellin, and xanthotoxin and higher concentrations of sphondin than populations lacking this parasitoid, presumably to reduce negative effects on parasitoid fitness. Metabolism rates for five furanocoumarins did not differ among five webworm populations from New Mexico to Alberta. All displayed rates near reported maximum values. Lutein content of fruits did not vary with UVI, but lutein sequestration by sixth instars was significantly correlated with UVI. UVI, lutein sequestration, and C. sosares may all be factors that interfere with webworm-host plant interaction in these western populations. |
