Biocontrol Scores Knockout Punch On Birch Tree Pest

The birch leafminer, an insect pest that regularly disfigures birch trees, has been virtually eradicated in the Northeast. And the credit goes to entomologists from URI and other institutions who successfully introduced a biological control agent.

"Birch leafminers are no longer a pest in the Northeast," said Richard Casagrande, URI professor of plant sciences, who along with research associates Lisa Tewksbury and Heather Faubert were responsible for implementing and monitoring the introduction in Rhode Island over the last 20 years.

The program consisted of introducing a natural enemy of the birch leafminer, a parasitoid called Lathrolestes nigricollis, which was brought to the U.S. from Europe where it effectively controls the birch leafminer.

Now the same can be said for Rhode Island, Massachusetts, Connecticut, New York, Pennsylvania and northern New Jersey. The URI scientists recently coordinated a survey that has documented complete control of this pest in these states.

"We have not seen any damage in Rhode Island in four years," Casagrande said, "and it is highly unlikely that we'll see problems with it again."

According to scientists, the birch leafminer arrived in the U.S. in 1923, probably in a shipment of plant material sent to Connecticut. From there it spread throughout the Northeast and into the Midwest. In the 1970s, Roger Fuester and colleagues at the Delaware Beneficial Insects Rearing Lab introduced several European parasitoids to fight the pest, and one of them, Lathrolestes nigricollis, became established in the Mid-Atlantic States. Later, groups from URI, the University of Massachusetts, and the New Jersey Biological Control Laboratory released more of the parasitoids in their respective regions.

The URI team began releasing the adult parasitoids in 1989 at Ryan Park off Oakhill Road in North Kingstown, and they have been monitoring the site ever since. The parisitoids spread quickly, but the build-up in population went slowly, Casagrande said.

The birch leafminer is not a fatal pest to birches. It disfigures the trees by mining within the leaves, and since birches are often used for landscaping, the effect became an aesthetic issue. Birches do have a fatal pest—the bronze birch borer – which can kill white-bark birches very quickly, but no biocontrol has been found for this native pest.

Casagrande said it is satisfying to be able to state publicly that a biocontrol program has succeeded.

"It takes lot of people and lots of cooperation to pull it off," he said. "Biological control systems such as this can be quite inexpensive and result in permanent, selective control of target pests."

URI, he notes, is coordinating a new regional research project intended to assist researchers working on a number of other important insect pests and weeds.

"The birch leafminer program is a good example of the results of a coordinated, long-term approach to classical biological control," Casagrande said. "We're seeing similar success with programs for purple loosestrife, cypress spurge, mile-a-minute weed, and perhaps, lily leaf beetle, but as you can see, it takes time—34 years in this case for complete control."