Wild parsnip pollination in the absence of herbivory: A tale of two hemispheres

Wild parsnips (Pastinaca sativa) in North America have been associated with a florivore, the parsnip webworm (Depressaria pastinacella), for over a century. In 2004, webworms were discovered in New Zealand (NZ), an area that has been free from herbivory since the 1800s. Herbivore-free parsnips in NZ are characterized by reduced levels of defensive chemicals but produce higher levels of certain floral volatiles, suggesting that some compounds might be under selection by pollinators in the absence of herbivory. We examined the floral bouquet of wild parsnips and its influence on pollinator attraction. Volatiles and floral visitors were collected and quantified from parsnips in the US and in NZ. Large muscoid calyptrate flies and small syrphids were effective pollinators in both NZ and the US. In the US, β-pinene, γ-terpinene, hexyl butyrate, octyl butyrate, germacrene D and an unknown monoterpene were all positively correlated with visitation by large calyptrates and small syrphids. In NZ, trans- ocimene, carene and octyl butyrate were positively correlated with visitation. Remarkably, most compounds positively associated with visitation are produced in significantly higher proportions in NZ flowers, suggesting that NZ flowers, in the absence of specialized florivores, may be chemically better constituted to attract pollinators.