Evolution in wild parsnip (Pastinaca sativa) chemistry after escape and reassociation with a specialist herbivore (Depressaria pastinacella)

Wild parsnips in North America have been associated with a detrimental florivore, Depressaria pastinacella, the parsnip webworm, for over a century. In 2004, webworms were discovered in New Zealand (NZ), an area with parsnip populations that have been free from herbivory since the 1800s. We predict that escape from and subsequent reassociation with a specialist herbivore will result in changes in plant chemistry that reflect selection by both an antagonistic herbivore and mutualistic pollinators.

We established a common garden with wild parsnip individuals from populations in the US and from infested and non-infested NZ populations. We measured oviposition preference, cateripillar damage, pollination success, leaf and floral chemistry. Our findings indicate that US and NZ populations differ significantly in chemitry, oviposition success and damage.