In New Zealand, the newly arrived parsnip webworms are a major selective agent, Zangerl said, wiping out a majority of the flowering parsnips.
The altered chemical defenses of New Zealand parsnips are probably allowing the webworms to feast on most of the plants in any given locale, Berenbaum said.
The parsnips chemical defenses normally include a good dose of furanocoumarins, a class of organic compounds that can be toxic to insects that eat the plant. While the parsnip webworm has evolved to tolerate large doses of furanocoumarins in its diet (it can eat up to 5 percent of its body weight of these toxins) the chemicals do limit its capacity to inflict damage.
What isnt clear is whether the absence of parsnip webworms in New Zealand for more than 100 years allowed the parsnips to let down their guard, Berenbaum said.
Parsnips have been in New Zealand since the 19th century, she said. Absent an aggressive enemy like the webworm, the parsnip had no reason to keep producing large amounts of furanocoumarins.
It could be simply that the parsnips have had 100 years to relax, Berenbaum said.
Other factors may explain the lower levels of certain furanocoumarins, however, she said. It could be that the parsnips that were first brought to New Zealand had less of these chemicals to begin with. Or perhaps the soil or climate influenced their evolution.
The appearance of parsnip webworms in New Zealand offers an appealing research opportunity, Berenbaum said. The researchers will be able to measure any changes in plant chemistry that result from the webworm infestation.
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|Contact: Diana Yates|
University of Illinois at Urbana-Champaign