Released moth to combat invasive
swallow-worts
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.
“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.”
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| Hypena opulenta caterpillar in the lab. Photo by Nora Lewis |
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.
