July 28, 2003

Beetles Winning Battle Against
Pesky Purple Loosestrife
By Elizabeth Omara-Otunnu

hile many gardeners spend the growing season locked in battle with the insect pests that damage their plants, Donna Ellis is giving a handful of herbivorous insect species some encouragement.

Her battle is against an invasive plant, purple loosestrife, Lythrum salicaria, and she has enlisted several species of beetle as her allies.

Each summer Ellis, an extension educator with the College of Agriculture and Natural Resources, travels around the state releasing thousands of beetles in areas where purple loosestrife has gotten out of hand.

Since the project, part of a nationwide program, was launched in Connecticut in 1996, more than a quarter of a million of these beetles have helped reduce purple loosestrife in the state to more manageable proportions.

Donna Ellis, an extension educator, stands beside Mirror Lake on the Storrs campus with purple loosestrife plants that have been eaten by Galerucella beetles. The beetles were introduced to control the invasive plant. Photo by Dollie Harvey

Purple loosestrife, found in wetland areas, does damage to the environment. It spreads aggressively, crowding out native plants and eliminating food and nesting places for wildlife and birds.

It was brought to North America by European settlers about 200 years ago. In the absence of its natural enemies, it spread throughout the United States.

Many invasive plant populations begin with a slow growth phase, says Ellis. "That's the time to control them," she says, "but they're often not recognized as a problem at that stage."

Controlling purple loosestrife is difficult, she says. The plant produces a large quantity of very tiny seeds - up to 250,000 seeds per plant - each year that are dispersed by air or water, or by adhering to animals or humans. It also has a strong taproot that continues to provide food to the plant when it is mowed, sprayed with herbicides, or damaged by insects.

In its native Europe, it is held in check by several species of beetles, and it was to these that scientists turned in the 1990s to launch biological control programs sponsored by USDA and Cornell University.

There are now 40 sites in Connecticut, where four different types of insect, all natural enemies of purple loosestrife, have been released: two species of Galerucella beetles that eat the leaves and stems of the plant and are the most widely used for controlling purple loosestrife; Nanophyes, a weevil that feeds on the flower buds; and Hylobius, a weevil whose larvae tunnel through the roots.

Biological control is seen as a sustainable, cost-effective, and long-term approach to reducing invasive species. The method was pioneered in the United States in the late 1800s with the successful importation of the Vedalia beetle to control scale insects that were wreaking havoc in citrus orchards. Sometimes, however, the imported species has a negative environmental impact too.

But although the introduction of any alien species carries some risk, says Ellis, "these insects are very specific. They eat primarily purple loosestrife, not other wetland plants or crops - not even other plants in the loosestrife family."

Ellis raises the insects at the Department of Plant Science research and teaching facility in Storrs. She sets two dozen potted specimens of purple loosestrife in plastic wading pools, places up to 20 Galerucella beetles on each plant, and envelops both plants and insects in white netting.

Within six weeks, the beetles have multiplied - 20 adults may produce a new generation of 1,400 beetles - and are ready for release in an infested area.

After setting the insects loose, about 5,000 at a time, Ellis and her colleagues monitor the site for up to five years, recording the extent of the purple loosestrife incursions, the insect count, and the amount and variety of other vegetation.

"We're learning a lot about different sites," she says. "You have to be patient with biocontrol. Some people are used to spraying a herbicide and a week later, the plants die. But with biocontrol, the work is not done after one year. For the first couple of years you often don't see a lot of impact."

The project is now yielding demonstrable results. Ellis is particularly proud of a site in Southbury, where photos of the same location taken three years apart show how the once prevalent purple spikes have yielded to a far greater diversity of vegetation since the beetles were introduced.

"The goal is not to eradicate purple loosestrife, but to control it," says Ellis. "These plants shouldn't be the main component of the environment."

In most sites, she says, once purple loosestrife recedes, other plants rebound on their own. Control of this invasive plant must be ongoing, however. In a dry year, for example, when the water level of a pond goes down, seeds deposited in the mud that's now exposed can grow into new plants.

"That's the beauty of biocontrol," says Ellis. Unlike mowing or spraying, which have to be repeated, once the insects are released at a site they remain there.

In addition to releasing the beetles, Ellis works to promote public awareness of purple loosestrife and other invasive plants.

"Identification is key," she says, "and learning what the options are. It's important to watch something that may get out of control later - one stem is so much easier to take care of than a large area of plants."

Although cultivars of purple loosestrife, with their brilliant spikes of magenta flowers, were once popular garden plants, most nurseries no longer sell them.

A pamphlet distributed by UConn's Cooperative Extension System - "Purple Loosestrife: Beauty or Beast?" - alludes to the plant's deceptive appearance. "Many people are surprised when they find out about the negative aspects of this plant," Ellis says.

She encourages local groups, such as school children, scout troops, and nature enthusiasts, to raise their own beetles and help monitor purple loosestrife sites.

New state legislation on invasive plants was passed in May that will establish a statewide invasive plants council to continue promoting education about invasive species and make recommendations to state government about banning or prohibiting specific non-native plants.

If you are concerned about the spread of purple loosestrife or other invasive plants at a particular site, send e-mail, including a digital photo if possible, to: Donna.Ellis@uconn.edu.