URI’s Biocontrol Laboratory heading project to fight invasive weed

Released moth to combat invasive swallow-worts

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Hypena opulenta caterpillar
Hypena opulenta caterpillar in the lab. Photo by Nora Lewis

KINGSTON, R.I.–July 31, 2018–After more than 10 years of research, scientists at the University of Rhode Island’s Biocontrol Laboratory have released a species of moth collected from Ukraine to help control invasive black and pale swallow-worts.

Swallow-worts are invasive vines native to Europe that were introduced into North America in the 19th century, and quickly spread along the East Coast and into Canada. Not only do they outcompete native species and alter soil chemistry, but they harm Monarch butterfly populations. Because swallow-wort is so closely related to milkweed, Monarch butterflies lay their eggs on swallow-wort leaves, but when the eggs hatch the larvae are unable to survive on the plant.

Graham and Tewksbury in the Lab
Recent graduate and student worker Courtney Graham, left, and Laboratory Manager Lisa Tewksbury analyze Hypena opulenta larvae in the Biocontrol Lab. Photo by Nora Lewis

“Swallow-wort was one of those weeds becoming increasingly problematic,” said Aaron Weed, of Tunbridge, Vermont, a former PhD student at URI that spearheaded the project. Back in 2005 when Weed started his research as a URI graduate student, there was increasing interest in controlling swallow-worts. Since then, he’s seen the vine spread aggressively. It thrives in several different environments, like pastures, forests and urban spaces.

“Integrated management of weeds is a very challenging endeavor,” Weed said. “Biocontrol is potentially efficacious for swallow-wort because conventional methods just weren’t working or were incompatible in sensitive areas.”

Weed ventured to Europe to try and find natural enemies of swallow-worts and brought back several insect species to test at URI’s Biocontrol Lab. Among them was the Hypena opulenta, a small moth collected from southeastern Ukraine, that the lab found feeds exclusively on swallow-wort species. Weed worked with Lisa Tewksbury, URI’s Biocontrol Lab manager, and Richard Casagrande, Professor Emeritus of entomology at URI, to conduct years of research on the biology of Hypena opulenta and its impact on swallow-worts.

Read more about student involvement in the Biocontrol Lab.

Hypena opulenta was a suitable candidate because it uses swallow-wort exclusively as its host plant, and reproduces several times a year. Its larvae have the potential to cause significant harm to the plants, according to Tewksbury.

URI received the permit to release the moths in 2017, and field tests in controlled cages were conducted in Charlestown, Rhode Island and Massachusetts the same year. Tewksbury has been monitoring the releases this spring, and if they’re successful, she said the lab plans to work with other local agencies to share resources and release the moths in other areas.

Tewksbury’s lab found the first moth that emerged in June, but hasn’t seen any others emerge yet. Tewksbury hypothesized that Rhode Island’s unusually cool temperatures throughout the month of June may delay the moths’ emergence, and added that this is the first time that we’re seeing the emergence of this species in New England.

“The goal of biological control is to reacquaint new pests with their historical natural enemies,” Tewksbury said. “This restores the evolutionary relationship of an insect with its host plant, which we hope will provide long-term management of the invasive plant species.”

Continued research is needed and underway to assess how well this insect will control populations across New England. “Since insects are impacted by the health of their plants, the local climate, and the health of plants is affected by site conditions, we still need to determine under which site conditions biocontrol impact is likely to lead to weed suppression,” Weed said.