PULLMAN, Wash. — Four species of beetles imported from Europe seven years ago are happy homesteaders in Grant County. They are feasting on the leaves and roots of an aggressive weed known as purple loosestrife.
Within three years of the insects’ introduction, stands of the aquatic plant have begun to disappear. “It’s been very dramatic,” said Gary Piper, Washington State University entomologist. “It’s probably the best biocontrol project I’ve worked on in a long time.”
In its simplest terms, biocontrol is the deliberate use of one living organism to control another. “The aim of biocontrol is to restore the natural balance between a weed and the environment by introducing insects and pathogens from the plant’s native homeland,” Piper explained.
Purple loosestrife, a Eurasian import, is a worthy opponent.
According to various reports, Lythrum salicaria, as it is known botanically, was introduced to the east coast both accidentally and intentionally in the early 1800’s. Accidentally, seed may have been brought to this country in the fleece of imported sheep or in ship ballast. Ballast was often soil dug near ports. It was dumped offshore when the ship made port giving floating seeds a chance to sprout along the shore.
Immigrants probably brought purple loosestrife to the country as well. It was prized as an herb and as a garden plant. It boasts colorful spikes of attractive lavender flowers from late June into early September.
But, its beauty belies its nature.
Not content to stay in one place, purple loosestrife spreads along ditches and along the banks of streams, ponds and lakes. It crowds out cattails and other native wetland vegetation, threatening wildlife habitat.
Purple loosestrife also infests irrigation canals and waste ways. Unchecked by natural organisms that keep it under control in Europe, it has marched west and become naturalized in wetlands all across the northern United States and southern Canada.
Purple loosestrife was first discovered in Washington state in 1929 in the Puget Sound area. By the time anyone took serious notice, it had taken root in three-quarters of the counties in the state. Perhaps the heaviest infestation can be found in irrigation waste ways south of Interstate 90 in Grant County. “It was a sea of purple,” Piper said.
The weed is tough to stop because of its tremendous reproductive potential. Each year an adult plant releases millions of tiny seeds, about the size of ground pepper. Chop loosestrife down and it will re-sprout from detached stems and root fragments. Burn it, and it will re-sprout from its roots. Its dense root mass makes it difficult to pull.
“Chemicals, of course, were one of the first things tried,” Piper said. “There are a couple of chemical products that do work against purple loosestrife, but when you are dealing with chemicals in an aquatic environment, you have to jump through all kinds of hoops to get necessary permits and sometimes they are denied.”As part of a national effort, the U.S. Fish and Wildlife Service provided funding that enabled entomologists to look for insect pests of the plant in Europe.
A handful of the most promising were selected for further study before they were brought to the United States. “Continued studies verified that the insects were very host-specific and only attacked purple loosestrife,” Piper said.
“Eventually we requested a permit from the U.S. Department of Agriculture Animal Plant Health Inspection Service. They gave us a permit to bring these insects into North America and make releases throughout the United States.”
The first insects deployed in the battle against purple loosestrife were two leaf-eating beetle Galerucella species. “Both species are very similar in their biology,” Piper explained.
The insects emerge as hungry adults in the spring from overwintering sites in the wetlands. They flock to young plants and chew on the leaves. The leaves lose water, shrivel and fall from the plant.
“Once they attack a plant very heavily, they move onto another,” Piper said. “By that time mating has occurred and the females start laying their eggs on the leaves or the stems of the plant. When those eggs hatch, the larvae, feeding in groups, strip all the chlorophyll-producing tissue from the leaves. They then move up the stem and eat the buds and flowers.
“It’s pretty impressive. You would think the plant was hit with a blowtorch. It just turns brown and dies.”
Since Galerucella, Piper has deployed Hylobius tranversovitattus, a large, nocturnal beetle that feeds and develops in the root system of the purple loosestrife plant.
“We’re dealing with a perennial plant that comes back from the roots every year,” Piper said. “The more tissue you remove, the weaker the plant becomes and it is less able to compete with other vegetation in the habitat.”
Piper has also introduced a fourth beetle — Nanophyes marmoratus — that attacks the seed capsules.
Why do you need more than one insect for the job?
“My opinion has always been that you should not just depend upon one or two species of insects for weed control,” Piper said. “The more kinds you put out, the better your chances for long-term control.”
While it sounds simple enough, the process of introducing new insects is a bit more complicated and tedious than opening a jar of insects at the release site with a courteous: Hyplobius meet purple loosestrife.
“When we got Hylobius in, we did not get adult insects. Eggs were shipped to us,” Piper explained. “So I had to act as a female insect myself and more or less go out and manually inoculate plants one-by-one with these eggs. Eventually we got a population going.
“We still use that technique in part. We confine a number of females in a cage with cut stems of purple loosestrife. They lay their eggs on the stems or down in the Styrofoam where we stick the stems.”
Out in the field Piper cuts the tops of stems, pokes a hole in the mushy part of the stem and sticks in an egg and covers it with a piece of clay, then moves onto the next plant, repeating the process several thousand times.
“It’s labor intensive, but it does get you a population of adults established at the site,” Piper said. “Once the adults get established, they will take over that function and do what they’re supposed to do in nature.
“Once the insects became established where we could go in and collect large numbers, we began making them available to interested individuals.”
During the last two years, the Washington Noxious Weed Control Board has hosted field days at the Grant County release site and has invited representatives of state and federal agencies and private landowners to come and collect insects to take back to their own weed- infested sites.
“Based upon the success we’ve had in the last few years with biological control, I think a lot of people are saying this is better than chemicals and cheaper too. You only need a couple thousand insects to start an infestation. A couple people can collect that many in an hour-and- a-half.”
For Piper, success brings more work. He is tackling 16 other noxious weeds. “I’m it as far as biocontrol of weeds in the state goes. I’m running all the time.”
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