Chemical mediation of oviposition and damage: Wild parsnip, Pastinaca sativa, volatiles influence parsnip webworm, Depressaria pastinacella, adult and larval host choice

The parsnip webworm, Depressaria pastinacella, is a highly specialized florivore on wild parsnip, Pastinaca sativa. Webworm adults oviposit on leaves of overwintered rosettes and the larvae feed on buds, flowers and immature fruit of the flowering stalk. We identified parsnip volatiles that mediate adult oviposition and larval orientation. We conducted oviposition counts, measured florivore damage and collected leaf and flower tissue for GC-MS analysis. GC-EAG analysis of female moth antennae with leaf volatiles revealed distinct depolarization for cis- and trans ocimene as well as beta-farnesene. Ocimene and beta-farnesene levels differ among populations and are positively associated with oviposition counts, suggesting that these compounds may function as kairomones. By contrast, larval damage was inversely associated with furanocoumarin content and positive associated with octyl butyrate. We compared leaf and floral volatiles to determine if adult host choice matched larval suitability.