August 18, 2011

Swallow-wort Biocontrols Pass Test

by MARY WOODSEN
Northeastern IPM Center

Entomologists Richard Casagrande and Heather Faubert helped rid a Rhode Island farm of cypress spurge, an invasive weed, in the late 1990s. The spurge is a pretty thing but a thug nonetheless, and poisonous to cattle. Their weapon: a cadre of hungry beetles, biocontrol agents so keyed into spurge they won’t eat anything else.

“Then,” says Casagrande (Univ. of Rhode Island), “along came swallow-wort.” Now Casagrande is leading a team to help find biocontrol foes to take on swallow-wort, research backed by Northeast IPM Partnership funds.
A menace to monarchs

Swallow-wort is ornery enough to land two botanical monikers. Vincetoxicum spells it out: this plant is poisonous. And Cynanchum means “dog strangler” or “to choke a dog”: take your pick. But swallow-wort has acquired new meaning in the Northeast. This rampant invasive smothers small trees and native toughies like goldenrod, practically swallowing them whole.

Because swallow-wort is related to native milkweeds, Casagrande’s grad student Jennifer Dacey wanted to see how well swallow-wort could provide for monarch butterflies. Results: 100 percent of monarch larva died when hatching on black swallow-wort. “They stopped eating after a single bite,” says Casagrande...

Working off a TAG (technical advisory group) test-plant list approved by the USDA’s Animal and Plant Health Inspection Service, Casagrande’s team examined five possible biocontrol specialists in their quarantine lab, including two moths that evolved to feed on swallow-wort leaves. The researchers wanted to be sure these biocontrol insects wouldn’t jump to plants on the TAG list, since the last thing anyone wants is a new pest dominating the landscape...

The TAG list includes, naturally, most native milkweed relatives and even their sixth cousins. “Luckily, none of our native plants are closely related to swallow-wort,” says Casagrande. “That makes it a great candidate for classical biological control.” ...

Results? Both leaf-eating moths “passed the acid test,” says Casagrande. But isn’t it risky to welcome in guests who die when the serving platter is empty? Considering how rampant swallow-wort is, these two could be fat and happy for many years to come. Next steps? Strategizing with U.S. and Canadian colleagues on best practices for releasing this deadly duo.

Read the full article at link.

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