When Stephen Schneider was an intern at the Arnold Arboretum of Harvard University in 1999, he was often given the grueling assignment of trying to weed out swallow-wort, an extremely invasive plant, from the park by hand, a task that could feel Sisyphean, given how aggressively the leafy vines grow.
“It’s just a real nasty weed,” said Schneider, who is now the Arboretum’s director of operations and public engagement. “We would spend weeks out of the year trying to, I wouldn’t even say eradicate it, but just control it.”
But thanks to a pilot program in partnership with researchers from the University of Rhode Island’s Biocontrol Laboratory, future interns given the chore of combating swallow-wort — or anyone trying to deal with it, for that matter — could one day have the assistance of an unlikely partner: the Hypena opulenta, a species of moth native to Ukraine whose larvae feast exclusively on the perennial herbaceous vine’s leaves.
In late June, Biocontrol Lab researchers, who have been studying the effects of the moths on swallow-wort for more than a decade, set up a mesh, tent-like structure on the Arboretum’s grounds around a section of land where the plant was thriving.
Experts then filled the see-through tent with dozens of male and female moths and let the insects get to work.
The results, according to Lisa Tewksbury, manager of URI’s Biocontrol Lab, were something worth celebrating.
A couple of weeks after releasing the moths into the controlled space, researchers returned to find a collection of eggs as well as some newly hatched larvae on the leaves of the swallow-wort. A week later, additional larvae as well as leaf damage were present.
Finally, by July 15, the larvae inside the tent had seemingly done their job, chewing away at and defoliating the invasive plants, according to the Harvard Gazette, the university’s official news publication, which first reported on the project this week.
“At the beginning you saw a little bit of feeding and then when they got larger they started chomping big holes out of it,” Tewksbury told the Globe. “I was practically jumping up and down. I was very happy.”
There are two types of swallow-wort, part of the milkweed family, present in North America, according to the University of New Hampshire: black swallow-wort and pale swallow-wort.
It’s believed, the school’s website says, that the invasive was introduced intentionally to the region sometime in the mid-1800s for horticultural purposes.
According to a “control fact sheet” on the city of Cambridge’s website, the plant is first referenced in “Gray’s Manual of Botany” in 1867 as having escaped from a garden in Cambridge.
The weed can have “severe consequences for the environment,” according to UNH, but it is commonly found growing in people’s gardens or twining around fences.
Some residents and municipalities have declared war on the plants over the years, fighting it off by hand and with pesticide to no avail.
It’s so pesky that it “breaks off at the ground and the roots quickly sprout again.” What’s more, “it disperses its seeds by wind,” according to UNH’s website, and continues to grow “readily in both shade and full sun, forming dense mats.”
“It’s quite a nefarious weed,” said Schneider. “It’s like a plague.”
The lab’s research on the relationship between the weeds and the moths began back in 2006, under the supervision of Richard Casagrande, a former entomology professor at URI; Tewksbury; and two graduate students.
Canadian researchers made the first release of the moths back in 2013.
But since this type of biocontrol is more tightly regulated on US soil, the Gazette reported, researchers here had to first conduct years of rigorous research in the lab before getting to that point.
“There is concern about the safety of biocontrol, generally resulting from adverse impacts of accidental introductions,” Casagrande told the Gazette. “Nobody is more concerned and careful than we are.”
Tewksbury said that the biocontrol lab tested a total of 79 species of plants in its quarantine lab to ensure that the moths didn’t feed on them.
“No species tested was able to support complete development of the Hypena larvae,” she said.
In August 2017, the United States Department of Agriculture approved the lab’s field release of the moths as a biological control agent, giving experts studying the link between the plant and insects freedom to take the research into the wild.
Last fall, Tewksbury said, officials from the Arboretum approached the lab and expressed interest in their ongoing research, citing the plague of swallow-wort on park grounds.
Having previously done similar releases of the moths on Naushon Island — one of the Elizabeth Islands off Southeastern Massachusetts — and two sites in Rhode Island, Tewksbury and researchers saw the Arboretum as a good place to continue their work.
Tewksbury said the initial release this summer was “very promising.”
But researchers won’t consider the pilot a complete success until two things are accomplished, she said: First, they want to see the arrival of moths currently pupating near the test site in the Arboretum come spring, an indication that they’ve established the population of the “biocontrol agent.”
And second, researchers eventually want to see a reduction in the amount of swallow-wort due to the feeding habits of the moths.
“We’re obviously hoping there are enough pupating that we will have a good emergence next spring,” she said.
As for Schneider, of the Arboretum, he said he’s hopeful that this could be a viable solution to fighting off swallow-wort, so more time can be spent on other, more important tasks.
“We have hit this plant with chemicals, organic controls, concentrated vinegars, and what-not, and all these things would do minimal damage,” he said.
“This was the healthiest damage that we have ever seen dealt to this plant, without a mower going over it. It really could free up horticultural time that could be spent taking care of the other plants and beautifying the landscape,’’ he said.