Several years of aerial spraying across Northeastern Minnesota appear to have failed to keep tree-eating gypsy moths from expanding, with the Minnesota Department of Agriculture reporting the number of moths captured doubled this year over last.
The department set 23,693 traps across the region this year and caught 27,870 moths, more than double those caught in 2008, the state reported Monday.
The moths have been found in pockets of Cook, Lake and St. Louis counties in recent years. It had been hoped that aerial spraying would kill enough to slow their spread.
Gypsy moths, originally invading from Europe, have been moving from east to west across the U.S. for more than 100 years. Their westernmost front now splits Wisconsin, with areas back to the East Coast generally infested.
But because the moths can hitchhike on vehicles, they already have moved into pockets ahead of the front, including along Lake Superior's North Shore.
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"We're probably seeing a combination of natural spread and accidental introduction by people moving infested materials in from states to the east or from Canada," said Geir Friisoe, plant protection division director for the Minnesota Department of Agriculture. "We've conducted several gypsy moth treatments in Northeastern Minnesota in recent years, and the evidence shows we've had success controlling the population in the areas we've treated. Unfortunately, the moths keep coming."
Friisoe said eradication treatments in Minnetonka and Richfield, Twin Cities suburbs, were successful in eliminating gypsy moth populations.
Gypsy moth caterpillars can defoliate large sections of forest, with oak, poplar, birch and willow among their preferred hosts. Because they have little or no natural enemies when they move into an area, they can hit some forests hard, especially forests already stressed by bugs or drought.
