Gypsy moth numbers increased some from 2014 to this year in Minnesota but could spike even higher next year after a warmer El Nino winter.
That was the word Tuesday from the Minnesota Department of Agriculture which reported 1,049 gypsy moths trapped this year, up from just 523 moths in 2014 but still well down from the record high of 71,000 in 2013.
Almost all the moths trapped have been in Northeastern Minnesota.
Researchers say the 2014 population drop reflected a severe winter, especially in northern Minnesota. But predictions of a warm or even normal winter have pest experts on guard.
While extreme cold can knock back moth numbers some, a typical cold winter actually helps the eggs survive, said Dr. Brian Aukema of the forest insect laboratory at the University of Minnesota.
"Populations often take some time to rebound after drastic crashes such as the one caused by the (unusually cold) winter of 2013-14," Aukema said in a statement. "But while moth populations may be knocked down, they are not knocked out. They have doubled in the past year ... and a normal winter will provide the egg masses the chilling requirement they need to hatch in the spring without killing them."
One surviving female gypsy moth can lay an egg mass that will produce more than 500 caterpillars the next year, said Kimberly Thielen Cremers, the state's Gypsy Moth Program Supervisor.
State and federal regulators last year invoked a quarantine for gypsy moths in 2014 for Lake and Cook counties after data showed a reproducing population had established itself in the area, the first major outbreak in the state. The quarantine is hoped to prevent people from accidentally spreading gypsy moths by moving infested wood and trees. Outdoor items in the quarantined counties such as logs, firewood, camping equipment and patio furniture that could be infested with gypsy moths must be inspected and certified as gypsy-moth-free before it can be moved to a non-quarantined area.
Gypsy moths, which are invaders from Europe, eat the leaves of many trees and shrubs. Severe, repeated infestations can kill trees, especially when the trees are already stressed by drought or other factors, state officials noted.
Slowly marching from east to west across the U.S. for more than a century, the gypsy moths have taken hold along the North Shore in recent years. Efforts to curtail their numbers have been unsuccessful and now north-central Minnesota has become the frontline in the federal effort to slow the spread west.
Gypsy moths could move only a few miles each year on their own. But their spread has been helped along by unknowing tourists and others who transport gypsy moth eggs from infested spots to uninfested areas, where they hatch and spread.
The spread often correlates with popular travel routes, campgrounds and parks that are tourist destinations.
State officials also are hoping that an imported fungus - released in 2010 from Duluth to Hovland along Lake Superior and inland near Tower and Ely - may attack and kill moth larvae. The fungus has been successful in reducing gypsy moth numbers in Wisconsin and Pennsylvania.