On the Job With URI's Pest Patrol
These scientists are fighting unwanted insects – with more insects.
When Jean Williams discovered a blood-red beetle with long black antennae consuming the lilies in her Wakefield garden a decade ago, she recognized it at once as an invasive insect she had just learned about in a master gardener class. University of Rhode Island researchers had been on the lookout for the new invader, which until then had not been found in South County. So she called URI entomologist Richard Casagrande, who verified that the insect was a lily leaf beetle, a Eurasian species responsible for wiping out populations of native and ornamental lilies in much of the Northeast.
Today, the beetle is not nearly the pest it was back then. That’s because Casagrande and colleague Lisa Tewksbury identified the beetle’s natural enemies in Europe, three species of tiny parasitic wasps, and have been raising and releasing small numbers of them wherever lily leaf beetles have been found in the region. The wasps lay their eggs exclusively in the larvae of lily leaf beetles, and when the eggs hatch, the wasp larvae kill and consume the beetle larvae from the inside.
“The wasps are such teeny, weeny little iridescent things that I had no fear of them at all,” says Williams of the insects released in her garden. “By the following year, they were definitely starting to control the beetles, and within a few years the beetles were mostly under control.”
Casagrande calls the parasitic wasp “fabulously successful” at controlling the lily leaf beetle. He and Tewksbury have released the wasps in numerous locations in Rhode Island and Massachusetts, and they have shipped them to New Hampshire, Maine, Connecticut and Ontario for release by partner researchers in those locations. Where the wasps have been released, the lily leaf beetle population crashes within a few years, making the wasp an ideal poster child for what is known as biological control.
The invasion of non-native species like the lily leaf beetle is a growing problem that has significant implications for native biodiversity, human health and the economy. Once an invasive species becomes established, it is a costly and challenging undertaking to get rid of it using chemical pesticides, mechanical means and other strategies. Despite the research required to do it safely, biological control — what the United States Fish and Wildlife Service calls the purposeful use of an invasive species’ natural enemies to reduce populations — is often the most successful strategy for eradicating invasives.
“In classical biocontrol, we reacquaint a pest with the insects that controlled them in their native land,” says Casagrande. “It’s useful on both invasive weeds and insect pests. It’s cheap, effective, safe and a long-term solution to regional problems.”
Biological control efforts got their start in the United States in the late 1800s when an Australian ladybug was released in California to fight the cottony-cushion scale, an invasive insect native to Australia that was killing the state’s citrus trees. The effort cost about $1,500 and permanently solved the problem. Since then, researchers have identified hundreds of insects that could be used to control a wide variety of invasive species, from agricultural and forest pests to aquatic weeds.
The key, however, is ensuring that the biocontrol agent — the insect being introduced — does not become a pest itself and start killing non-target species. That’s what happened in 1917 when a tachinid fly was released to fight gypsy moths and was later found to also kill the caterpillars of cecropia moths, luna moths and other popular and beneficial insects. So years of testing are now conducted to ensure that the control agent preys only upon the targeted invasive species, what Casagrande calls “total host specificity.” Several government agencies must approve permits to release any insects into the environment.
The need for total host specificity is the reason for the highly secure quarantine facility at URI’s Biocontrol Laboratory in Kingston. The security measures at the lab are not in place to keep people from getting into the lab, but to keep unapproved insects from getting out.
After punching in a security code to open the door, Tewksbury walks into a small dark entryway illuminated only by the lavender glow of a bug zapper above her head, placed there to attract and kill any flying insect that happens to escape from the lab. She says the entryway is “a room of last resort,” since it’s the last chance of containing insects that aren’t approved for release.
Once the secure door is closed, a second door opens into a prep room where researchers don lab coats before beginning their work. It’s here that all plant material and soil destined to be discarded is first heated in an autoclave to 123 degrees Celsius to ensure that unseen insects don’t accidentally escape.
Three doors from the prep room lead to modest white rooms, each housing Plexiglas cages for rearing insects. In one room, student Katharine Harrison raises Hypena moth caterpillars, which eat nothing but black swallowwort, an invasive vine that forms dense patches in a wide variety of habitats and may be harmful to monarch butterflies. Like prisoners awaiting furlough, the caterpillars live out their lives in clear plastic bins containing fresh swallowwort leaves as they wait for government approval to be released.
A second room is filled to capacity with additional cages of swallowwort and caterpillars in various stages of growth, while the last room contains stacks of bins filled with stalks of invasive Phragmites, an attractive reed that chokes out wetlands. The Phragmites had been collected earlier in the day for another insect to feed upon. This one, a European moth, burrows into the sides of the plant stem and eats the entire length of the stem from the inside, eventually killing the plant. Student workers are testing new methods of rearing the insects.
Outside the quarantine area and down the hall, lily leaf beetles are being reared in large chambers with lilies for further testing. A close look at the underside of the plants’ leaves reveals tiny lines of bright orange eggs, each barely larger than a grain of salt, and brownish beetle larva consuming the leaves.
When a good candidate for biocontrol is identified, someone from Casagrande’s research team (or a partner institution) visits the region where the species originated and seeks out its natural enemies. “Typically we do a quick survey to see what’s there, and then we contract with someone to work on the ground for a season or two,” he says. For pests native to Europe, he often works closely with the Centre for Agriculture and Bioscience International in Switzerland during the survey and early testing stages.
In the case of the lily leaf beetle, most of the fieldwork was conducted in France and Switzerland, where several related beetles are also found. But in a project to control the Colorado potato beetle, it required hiring a graduate student in Mexico, and combating black swallowwort involved sending URI graduate student Aaron Weed to Switzerland, Ukraine and Italy to survey for its natural enemies.
Once those enemies are found, specimens are brought to URI’s quarantine laboratory where they are tested to ensure they only kill the target species. If the target is an insect, like the lily leaf beetle, a dozen closely related species native to the release area are tested to ensure that the control agent doesn’t also attack the relatives. If the target species is a plant, a list of fifty to 120 other plants is compiled in cooperation with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) for testing.
“We test plants under ‘no choice’ conditions,” Casagrande says. “That means they have no choice what to eat. We expose the insect to each plant, and if they can live on it, they will; if they can’t, they die.”
It often takes several years of host specificity tests before the researchers are certain the control agent is safe to release. It took five years of testing before the parasitic wasps were approved to prey upon the lily leaf beetle, and even longer for the moth that eats swallowwort. When Casagrande is convinced, he petitions APHIS for a release permit.
URI sophomore Robert Healey and senior Shannon Cron examine lab research in progress.
Permission to release an insect to fight a pest insect is often granted in relatively short order. But that’s not the case when seeking to release an insect to control an invasive plant. Casagrande petitioned to release the Hypena moth to control black swallowwort in 2011, and after conducting a few additional tests requested by the APHIS technical advisory committee, it was recommended for approval. But it still needed to be reviewed by the Fish and Wildlife Service, which is charged with protecting endangered species.
“And it’s been hung up there ever since, along with every other weed biocontrol agent in the country,” says Casagrande, clearly frustrated by the situation, noting that a dozen agencies in four states are awaiting approval to release the Hypena moths. “Two weeks after the committee recommended approval, we were able to release it in Canada, and we’ve been releasing there ever since. But weed biocontrol is at a standstill in the United States at this time. Nothing is being released.”
Casagrande says that before signing off on a weed biological program, the Fish and Wildlife Service would like data on the biocontrol agent’s direct and indirect effects on all threatened and endangered species — nearly 3,000 of them.
“This is clearly impossible, but we do test those species that could reasonably be expected to be affected,” Casagrande says. And with personnel reductions at Fish and Wildlife, no one is making decisions of any sort on any release permits.
“So they don’t know what to do, and we don’t know what to do,” he adds. “We know it’s going to get sorted out, but we don’t know when.”
Casagrande has been interested in biological control since he was in elementary school. That’s when his family moved from New Jersey to a small town in North Carolina, where one of his neighbors conducted biocontrol experiments on tobacco plants. “He was a real Harrison Ford type,” Casagrande recalls. “We’d hunt and fish together, he told great stories, and I appreciated what he did. I’ve literally been collecting insects and working on biocontrol since age ten.”
After earning a doctorate at Michigan State, Casagrande joined the faculty at URI in 1976 and has been working on pest management and biological control ever since. In one of his first big successes, he collaborated with researchers at the University of Massachusetts and the United States Department of Agriculture’s Beneficial Insects Research Laboratory in Delaware to identify and raise a parasitic wasp that controls the birch leafminer, an invasive pest insect that disfigures white birch trees. The pest has now been controlled throughout the East.
Today, Casagrande’s lab maintains one of the most active biocontrol programs in the country. “We’re well known internationally for our work in biocontrol,” he says. “People in Rhode Island have no clue what we do, but if you ask people in Australia, France or South America, they know our work.”
Not every invasive species is a good candidate for biological control, however. Casagrande says a prospective species should first be a serious problem, one that isn’t easily controlled by other means. “You don’t see us working on dandelions,” he says with a smirk. “There are a lot of exotic plants that aren’t really a problem. If it’s not a serious problem, we won’t look at it.
“The most important step in classical biocontrol is choosing the right target,” he adds. “You want to spend a lot of time giving that some thought. It’s going to take at least a million dollars and probably a decade of research before you’re going to get to the point of petitioning for a release permit.”
So while he awaits his swallowwort permit, Casagrande and his team are continuing their research on several other invasive pests and their enemies. They are testing and releasing control agents for hemlock wooly adelgid, an insect that has killed most of the region’s hemlock trees; Cypress spurge, a European ornamental plant that reduces the grazing value of pastures; and purple loosestrife, a colorful flowering plant that degrades wetlands, among others.
They also regularly survey the area for new invasive species that they expect will arrive in the region from neighboring states. In the last two years, for instance, they discovered that tree-killing southern pine beetles have made their long-anticipated appearance in Rhode Island. Casagrande expects to find another tree-killer, the emerald ash borer, this year.
The researchers’ work isn’t finished once the control agents have been released, however. They must monitor the release sites for several years to ensure that the pest is being controlled. This summer, several URI students assessed plant density and damage at eleven sites where poppy seed-sized weevils had been released to fight mile-a-minute vine, an aggressive plant native to the Far East that arrived in Rhode Island in 2008 and has taken up residence in several communities.
At a site in Cranston, on property owned by the Providence Water Supply Board, it was easy to see that the weevils were hard at work. In a field of lush vegetation that included shrubs, wildflowers and grasses, the only leaves that looked lacy from being eaten were those of the mile-a-minute vine.
“To evaluate biocontrol, you really have to see what the plants and insects are doing,” says Tewksbury, pointing out the tiny weevils on the leaf tips of several vines. “The weevils are clearly established here, but they haven’t knocked back the mile-a-minute population yet. It might take some time.”
The weevils lay their microscopic eggs only on mile-a-minute leaves, and the larvae burrow inside the plant’s stem to feed. Although the weevils are difficult to see in the wild, when Tewksbury taps on a vine, about a dozen adult weevils drop into her hand and play dead until she places them back on the plant.
Tewksbury’s URI colleague Heather Faubert is monitoring bio control efforts against another of Rhode Island’s more recent invaders, the winter moth, a native of Europe that flies in annoying fluttery clouds between Thanksgiving and Christmas. According to an aerial survey by the Rhode Island Department of Environmental Management, winter moth caterpillars defoliated 27,000 acres of trees in Rhode Island in the spring of 2015.
To reduce their impact, Faubert has released thousands of parasitic flies in Rhode Island since 2011 in hopes that they will solve the winter moth problem. The fly lays its eggs on tree leaves, and when the moth caterpillars eat the leaves they also consume the eggs, which hatch inside the caterpillar and eat the caterpillar from the inside out.
To determine the success of last year’s release of about 14,000 parasitic flies, Faubert and URI junior Gennifer Keller collected winter moth caterpillars at each of seven sites in the state. Just beyond the parking area to the beach at Lincoln Woods State Park, they spread a blue tarp beneath a branch of a large maple tree and strike the branch with a broomstick several times, dislodging leaves, dirt and insects. They then sort through the fallen detritus and pick up any winter moth caterpillars they find.
Their plan is to collect 300 caterpillars, but they only find nine on their first attempt. So they drag the tarp beneath another branch of the same tree and bang it with the broomstick once again. This time they collect about thirty more caterpillars. “That’s more like it,” Faubert says. “We’re 10 percent there.”
She wasn’t expecting winter moth caterpillars to cause as much damage to foliage this year as they did last year, due largely to this year’s unusual winter and freezing temperatures in early spring. “But where they’re bad, they’re really bad,” she says, noting that apple trees and blueberry bushes at URI’s East Farm produced hardly any fruit this year. “But in most places they haven’t been as bad as last year.”
Glancing at the viburnum shrubs along the forest edge a few yards away, Faubert notices that the leaves appear to have been eaten by insects. So she drags the tarp to the shrubs, smacks the thin branches, and picks up about seventy-five more caterpillars. At the next shrub, her total caterpillar collection tops 275. She and Keller are more selective at the last shrub, picking up only the largest caterpillars that drop to the tarp.
Faubert feeds and raises the caterpillars in her lab until they pupate, at which point they are sent to a lab at the University of Massachusetts, where it will be determined whether they contain parasitic fly larvae or not.
“Our goal is to see that the flies are established,” she says. “In the first year we expect to find a low rate of flies in the pupa. If we get one out of 300 in the first year, I consider that a success. It took three years before we got our first fly detection at Goddard Park. But after they’re established, they’ll spread elsewhere.”
Richard Casagrande is confident that the parasitic fly is the answer to the winter moth problem in Rhode Island. It has already been successful at wiping out the moth in Wellesley, Massachusetts, where it was first released, so he is certain it will do the same thing in the Ocean State.
“We won’t know that the problem is solved in Rhode Island for a few years,” he says. “But we could walk away right now and I’m sure the problem will still go away. Not everyone knows that yet. The moths don’t know that yet. But they’re toast.”