Invasive Pest Knocked Out
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 between scientists from several universities in the Northeast, researchers have scored a knockout blow.
The birch leafminer (Fenusa pusilla), an insect pest that regularly disfigures birch trees, has been virtually eradicated in the Northeast. And the credit goes to entomologists who successfully introduced a parasitoid called Lathrolestes nigricollis, which acts as a biological control agent.
“Birch leafminers are no longer a pest in the Northeast,” said Richard Casagrande, University of Rhode Island (URI) professor of plant sciences, who has monitored and participated in leafminer control efforts for the last 20 years.
The parasitoid, a natural enemy of the birch leafminer, effectively controls the insect in its native Europe. Today, the same can be said for Rhode Island, Massachusetts, Connecticut, New York, Pennsylvania, and northern New Jersey. 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, 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 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.
“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.”
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