Master Gardeners: Winter’s Effect on Insect Populations

<p>Emerald Ash Borer  |  Photo courtesy of Julie Moore/submitted</p>

Emerald Ash Borer  |  Photo courtesy of Julie Moore/submitted

Has it crossed your mind that maybe this challenging winter will provide a payoff of sorts this summer in terms of fewer insect pests? Surely some insect bad guys won’t be able to survive? It seems only fair!

Dr. Phil Nixon, a University of Illinois Extension Educator in Entomology at the Urbana-Champaign campus has extensive knowledge in all aspects of insect lifecycles and environmental needs. Recently, I asked him if we will be rewarded with fewer insect pests this summer.

“Most of the insects that occur in Illinois range from Atlanta, Georgia up into Canada, so there are few changes in our insect fauna (environment) in warm and cold winters. In other words we would have to experience a winter colder than what is typical for International Falls, MN to see much of an effect on the insect populations.”

A phenomenon known as diapause happens in insects, triggered in the fall by decreasing daylight, which causes metabolic rates to drop dramatically. Nixon continued, “During fall, outdoor insects produce glycerol, ethylene glycol and other compounds to lower the freezing point of their cells (diapause). Anti-freeze that we add to our car radiator contains ethylene glycol. These and other factors set the supercooling temperature for individual insect species,” he noted. “Essentially, cold damage is much less in insects above the supercooling threshold.”

Does this mean that the Emerald Ash Borer population won’t be affected? Nixon stated, “Research found that EAB supercooled to 25 degrees Fahrenheit below zero, with little mortality above that temperature. From what I can tell, the coldest it has been in Illinois this winter has been 20 degrees below zero F in the Chicago area, so it has not gotten cold enough to be a factor.”

Will any insect pests be adversely affected by this winter? “Marginally hardy insects like mimosa webworm and honeylocust plant bug appear to be limited by cold weather. White grubs that feed on turfgrass roots migrate deeper into the soil to escape freezing temperatures but most Japanese beetles do not migrate deeper than eleven inches. If frozen for at least three weeks, the grubs will start to die… so far this winter, our soil has not frozen that deeply for that long, probably due to our having insulating snow cover when it has been the coldest.”

So, no summer payoff can be expected? “With few exceptions, it appears that reports of the cold weather reducing insect numbers have been more wishful thinking than reality,” Nixon stated.

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Julie Moore is a Master Gardener volunteer with the University of Illinois Extension in DuPage County.

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