Globalization of trade has exacerbated the problem of invasive plants; when weed species invade new areas, they can cause enormous economic and ecological damage. In many cases, toxic chemistry facilitates the process by which these weeds become established, but little information is available on the evolutionary changes in toxin content of plants that occur after introduction into a non-indigenous area and release from interactions with longtime insect associates. Even less is known about changes in toxin content that ensue when coevolved natural enemies resume interacting with a hostplant in a non-indigenous area. A unique opportunity has arisen in New Zealand to investigate this process as it unfolds. The parsnip webworm Depressaria pastinacella is native to Europe where it feeds on three plant species that contain toxic furanocoumarins. These three host plants invaded New Zealand 37 to 138 years ago and have been free of Old World herbivores until two years ago, when parsnip webworms were reported for the first time to be thriving on the South Island of NZ. The goals of this project are to determine whether furanocoumarin levels in New Zealand populations not yet infested by webworms are lower than levels in North American and European populations with a long history of webworm association and to determine whether New Zealand populations reassociated with parsnip webworms will experience directional selection for increased toxicity.
Broader Impacts: This situation provides an extraordinary opportunity to document the extent to which an invasion by a weed species depends on its toxic chemistry. As classical biological control involves introduction of herbivores to control invasive weeds, the results of this study will also provide essential information about how weeds might evolve subsequent to reassociation with a control agent and will be useful in the decision-making process involved in biological control programs involving introduction of coevolved herbivores.
