The Greeks knew it takes a thief to catch a thief. Today, taking a page from the ancients, scientists at the Arnold Arboretum of Harvard University are using one foreigner to combat another, but in this case it’s fauna against flora.
The target: swallow-wort, or Vincetoxicum nigrum or V. rossicum, a weed that is no stranger (or friend) to city gardeners or country strollers. Cambridge, in fact, distributes flyers asking residents to yank the seed pods when they see them; in woodsier suburbs, whole trees can be swamped with the climber.
Exuding toxins, smothering neighbors, and chemically tricking monarch butterflies into laying their eggs on leaves that kill the larvae, swallow-wort is a threat to biodiversity, and on a quest for domination. The foul-smelling, finely-rooted weed resists conventional controls such as pulling, mowing, and herbicides, so this summer, the Arboretum partnered with the University of Rhode Island’s (URI) Biocontrol Laboratory to become a release site for the defoliating moth Hypena opulenta, a species native to Ukraine whose larvae eat swallow-wort leaves. The three-year project will gather data showing whether the moth could serve as an effective biocontrol agent against the rapidly spreading, highly adaptable Vincetoxicum.
The alien invader’s threat to native insect and plant communities is so great that in 2005, URI researchers began investigating biocontrol options to conserve local ecosystems and the animals and insects that rely on them for survival. Biocontrol, when carefully and scientifically vetted, is a safe and effective alternative to pesticides, using living organisms or “natural predators” to reduce pest populations and invasive plants.
Richard Casagrande, the entomology professor emeritus who initiated the URI biocontrol program, said host relationships that developed over millennia mean that many insects rely on specific organisms for their development.
“Biocontrol specialists seek out these host-specific insect parasitoids, often wasps and flies, for controlling insect pests and weeds that are outside of their native range,” he said. “Centuries of experiences have shown these relationships to be stable in the new, introduced environments.”
Hypena opulenta was shown to be a safe and potentially effective biocontrol agent against swallow-wort by several seasons of field surveys and preliminary testing in Europe, the native habitat or both moth and weed, followed by studies at URI’s Biocontrol Laboratory, a U.S. Department of Agriculture (USDA)-approved quarantine facility.
“A plant like the swallow-wort is introduced into North America, but it doesn’t have a native insect to feed on it, so we have to go back to its place of origin to find, research, and potentially introduce the natural enemy to its host plant, while ensuring safety to the surrounding ecosystem,” said Lisa Tewksbury, a Biocontrol Lab manager who has worked on the project since its inception.
