What could be lower than the lowly parsnip, a root once prized for its portable starchiness but which was long ago displaced by the more palatable potato? Perhaps only the parsnip webworm gets less respect. An age-old enemy of the parsnip, the webworm is one of very few insects able to overcome the plants chemical defenses. The tenacious parsnip webworm has followed the weedy version of the parsnip in its transit from its ancestral home in Eurasia to Europe, North America and most recently New Zealand.
The long association of the parsnip (Pastinaca sativa) and parsnip webworm (Depressaria pastinacella) offers a unique window on the complex interaction of plant and insect enemies, according to a study appearing this week in the Proceedings of the National Academy of Sciences. And the recent appearance of parsnip webworms in New Zealand, more than 100 years after the parsnip first arrived there, offers the best view yet of how these species influence one another.
The research team, led by University of Illinois entomology professor and department head May Berenbaum, made two key findings. First, the researchers found, the New Zealand parsnips had significantly lower levels of certain chemical defenses than parsnips growing in Europe and North America, where webworms are a constant threat. Second, the New Zealand parsnip webworms were dramatically affecting the plants ability to reproduce. The webworm caterpillars eat the parsnip flowers and burrow into their stalks.
In certain populations affected by webworms, 75 percent of the plants were completely devoid of any reproductive parts, said Art Zangerl, a senior research scientist in the department of entomology and co-author on the paper. The affected plants were contributing zero fitness, which is really dramatic. We dont often see that.
Fitness is a measure of a species ability to successfully reproduce. Environmental factors that reduce the fitness of an
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University of Illinois at Urbana-Champaign