Voracious viburnum leaf beetles have munched their way south from Lake Ontario to Ithaca, Cornell entomologists say

beetle larvae feed
Paul Weston/Cornell University
The first (smaller) and second stage of viburnum leaf beetle larvae feed on a viburnum.

For the ravenous viburnum leaf beetle, a relentless southern march continues. The beetle (Pyrrhalta viburni) was found in the Ithaca and surrounding areas late last month by a Cornell University entomologist. The beetle had chewed its way through ornamental shrubs in several New York counties along Lake Ontario, leaving the skeletal remnants of once-beautiful bushes in its wake.

"We probably won't see much damage here for about a year," says E. Richard Hoebeke, entomologist, and an assistant curator of the Cornell Insect Collection. "If it follows what it did in Rochester, it's going to be a major pest. Right now the damage is minimal here, but this is the first year that the larval stage of this beetle has had a foothold in the area."

Hoebeke spotted the beetle May 22 at Sampson State Park on Seneca Lake near Ovid, N.Y. The following day, Hoebeke found the beetle at Taughannock Falls State Park, near Trumansburg, N.Y. He found the beetle for the first time on the Cornell Ithaca campus May 27. He even found the beetle on his own home property in Trumansburg.

This is third year the beetle has been seen in the central and western parts of New York. Hoebeke first discovered the viburnum leaf beetle along the Lake Ontario shore on July 5, 1996, at Fair Haven Beach State Park in northern Cayuga County. That summer he also found the pest in Monroe, Orleans, Niagara and Jefferson counties. The counties of St. Lawrence, Oswego, Ontario, Wayne and Genesee have since joined the growing list. Last year, Hoebeke found the beetle in Geneva, N.Y.

Currently, Paul A. Weston, Cornell senior research associate in entomology, is conducting research trials at the Highland Park Arboretum in Rochester, to find ways to eliminate the pest. He is testing a wide array of potential weapons, including natural predators like lady bugs, and he hopes to test parasitic wasps. Also, Weston is conducting studies to

determine what makes viburnums susceptible to the pest and other plants resistant. "It's not a surprise that the beetle was found in Ithaca. Considering how fast it has been expanding its range, we were expecting it here this year or next," Weston says.

Weston, Hoebeke and Brian C. Eshenaur, a Cornell Cooperative Extension agent in Monroe County, N.Y., have developed a viburnum leaf beetle fact sheet to assist homeowners, nurseries and landscapers in identifying the pest. The fact sheet is expected to be published in early July and will be available through county cooperative extension offices.

The adult beetles are hard to see, resembling a small, dark-brown blotch, about the size of the head of a large match stick. The young larvae have an off-white color, and in the second larval stage they develop black, uniform spots on their backs. Both larvae and adults are devastating to the ornamental plants.

An adult female can lay up to 500 eggs, and the larvae hatch from eggs in early May. They feed on the viburnum leaves throughout the larval period, which lasts four to five weeks. By early to mid-July, the adults appear and continue gorging on the remaining leaves. They then mate and lay eggs on the shrub's twigs.

First discovered in Canada in 1947, the viburnum leaf beetle could have traveled from Europe on nursery plants around the turn of the century, Hoebeke believes. It was not seen in North America again until 1955 at Font Hill, Ontario.

The insect then went undetected for 23 years, until it was found again in Ottawa, Ontario, and Hull, Quebec. Scientists have tracked its movement since. Hoebeke says that the leaf beetle caused severe defoliation of ornamental viburnums in the Ottawa-Hull region in 1978. The beetle attacked the popular European cranberry bush viburnum, (Viburnum opulus), as well as arrowwood viburnum (V. dentatum complex), American cranberry bush viburnum (V. trilobum) and maple leaf viburnum (V. acerifolium). Other viburnums, most notably leatherleaf viburnum (V. rhytidophyllum) and Koreanspice viburnum (V. carlesii) are virtually immune.

Homeowners or landscapers should contact their county Cornell Cooperative Extension office if they suspect the presence of the beetle on ornamental viburnum trees or bushes.

 

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