A common question after such a hard winter is how it will impact pest levels this summer. My answer is usually not as positive as some people want it to be. Contrary to common belief, a hard winter does not have much impact on most insect levels. University of Illinois Extension Entomologist Dr. Phil Nixon provides more on this topic below.
Most of the insect species that occur in Illinois range from Atlanta, Georgia into Canada, so there are few changes in our insect fauna in warm and cold winters. In other words, we would need to experience a winter colder than what is typical for International Falls, MN to see much of an effect on the insect populations. Even though we are experiencing a cold winter for our part of the country, it is probably having little effect on our insects.
During fall, outdoor insects produce glycerol, ethylene glycol, and other compounds to lower the freezing point of their cells. Anti-freeze that we add to our car's radiator contains ethylene glycol. These and other factors set the supercooling temperature for individual insect species. Essentially, cold damage is unlikely to occur in insects much above the supercooling threshold.
There have been recent reports that the recent cold weather in Illinois has affected emerald ash borer. However, research found that emerald ash borer supercooled to 25 degrees F 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 below zero F in the Chicago area, so it has not gotten cold enough to be a factor.
Some insects are marginally hardy in this climate, and their numbers may be affected. Mimosa webworm and honeylocust plant bug appear to be limited by cold weather, so their numbers might be reduced. White grubs that feed on turfgrass roots migrate deeper into the soil to escape freezing temperatures, but most Japanese beetle grubs do not migrate deeper than 11 inches. If frozen for at least three weeks, the grubs will start to die. In previous years, deeply frozen soils for several weeks have reduced Japanese beetle populations by about 2/3. In the northern half of Illinois, the soil has frozen deep enough and long enough to reduce the number of Japanese beetles next year.
With few exceptions, it appears that reports of the cold weather reducing insect numbers have been more wishful thinking than reality.
Want to learn more about managing pests in your home landscape? Attend our program Pest Control Strategies in the Garden on April 22nd (1:30 PM ) in Peoria or on April 24th (6:30 pm) in Havana. This program will help you decide the best options for managing those pests that seem to zero in on your landscape favorite while protecting the environment.
If you need help with a specific pest question, Talk to a Master Gardener on their Hotline at (309) 685-3140(309) 685-3140 ext. 13 Monday through Friday from 9:00 a.m. - 12:00 p.m. or email them at firstname.lastname@example.org.