Birch Leafminer Controlled in Northeast

birch leafminer damage photo by E. Bradford Walker, Vermont Department of Forests, Parks & Recreation

excerpts from a news release of the University of Rhode Island

The United States has been under assault for decades by a wide variety of alien plants and animals, and it is not often that one of these aliens faces a counterpunch. But in a collaborative project with several other institutions, the University of Rhode Island has scored a knockout.

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. 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.

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.

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.

"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."