The invasive plant sometimes called dog-strangling vine doesn’t harm pets, but it lives up to its name as a strangler, choking out native wildflowers as well as Christmas tree plantations and fields of prime alfalfa. In Northern New York, in Jefferson County, a nearly 1,000-acre tract on an island lies blanketed under this perennial Eurasian vine.
Dog-strangling vine grows in almost any soil type, has a prodigious root system, and is particularly good at making and dispersing seeds. It is so toxic that no North American bird, mammal or insect will eat it, and it bounces back from the most powerful herbicides. No wonder biologists and agronomists have been losing sleep over it.
So it’s with much relief that researchers at the University of Rhode Island announced they’ve recently located and vetted a worthy opponent for the invasive vine. While dog-strangling vine, more commonly known as swallow-wort, has withstood mowers, rototillers, flame throwers (true) and potent agrochemicals, it’s no match for this brute. At a tenth the weight of a paper clip and a fraction of an inch long, our hero is Hypena opulenta, the larva of a Ukrainian moth.
In its native range, swallow-wort is just another well-behaved native plant because the tiny green Hypena opulenta caterpillar, along with other insects, keeps it in check. In fact, Carleton University biologist Naomi Cappuccino, a Canadian researcher who went to Ukraine with URI scientists to look for biological controls, said they had a hard time locating any swallow-wort; it was that scarce.
Finding biological controls for an exotic invasive plant is no easy task, and requires traveling to the plant’s home environment(s) to make field observations in all kinds of conditions. But once an insect, pathogen or vertebrate is identified, the real work begins. Many years of quarantine with carefully controlled trials are required to make sure a potential hero won’t end up going over to the “Dark Side” and doing more harm than good, which has happened in the past.
This caterpillar won’t be USDA approved for release here until some time in 2014 at the earliest, but in Canada, 500 Hypena opulenta larvae were released near Ottawa in September 2013 in a cold-hardiness trial. The hope is that we’ll have a success story like the recent one with purple loosestrife, in which biological controls stopped it from harming freshwater wetland ecosystems. Even if Hypena opulent performs admirably, it may be a decade or more before we see the decline of the dog-strangler. To paraphrase Princess Leia, “Help us, Hypena opulenta; you’re our only hope.” Thus far, at least.
More information on black swallow-wort, pale swallow-wort, and other invasive species can be found online.
Swallow-wort photo courtesy of Purdue University Extension.