Falling Temperatures do not Necessarily Mean Fewer Insects
With record-breaking cold temperatures in much of the United States recently, newspaper headlines have suggested that the freezing weather this winter could mean fewer insects next spring. For example: “Celebrating Deep Freeze, Insect Experts See a Chance to Exterminate Off Invasive Species”. “The Upside Of The Bitter Cold: It exterminates Bugs That Kill Trees”. “Extreme cold may wipe out high percentage emerald ash borer larvae”.
While it’s true that insects will die if exposed to very cold temperatures for prolonged periods of time, many are able to survive, depending on the insect and the circumstances.
It’s Déjà vu All Over Again …
This is nothing new, of course. In fact, two years ago we faced a very similar situation when an extraordinarily mild winter gave rise to headlines about how the warmer temperatures would mean greater insect populations come spring. Mosquitoes for example would thrive, the thinking went, because of the lack of freezing temperatures.
However, leaders of the Entomological Society of America said “Don’t Bug Out Over Warmer Weather” in a press release, explaining that lots of other factors affect insect populations besides temperatures. “States like Alaska and Minnesota are famous for their brutally cold winters, and yet they are also known to have extremely active mosquito populations during the summer,” said ESA past President Grayson Brown, who explained that mosquitoes are even more affected by the amount of rain during the spring, since they need water to lay their eggs.
ESA’s past Vice President Robert Wiedenmann said that in some cases the warm winter could even cause harm. “Some insects that emerge earlier than normal because of warm temperatures may not find the appropriate food sources available and could starve,” he said. “Likewise, mild winters may favor the predatory or parasitic insects that help keep pests in check, and result in fewer pests. Insect ecology is affected by a number of factors and is not solely dependent on winter or spring temperatures.”
Long Story Short: It’s Complicated …
Which bring us to our current situation. While it’s true that extremely cold temperatures for prolonged periods of time can decrease insect populations, other factors are at play as well.
The Emerald Ash Borer (EAB) is a good example, since it has received so much press recently. Ironically, the recent cold spell could actually end up helping the EAB in certain areas because the freezing temperatures might harm EAB predators. A few years ago, scientists in Michigan and other states began releasing tiny parasitoid wasps that help control the EAB by laying eggs into or on the EAB larvae. “In general, parasitoids are more susceptible to stressors (e.g., pesticides, cold temperatures) than their hosts,” said Dr. Jian Duan, one of the scientists who has been rearing and releasing the wasps. “If this year’s cold temperature kills overwintering EAB larvae, it will surely exterminate the associated parasitoids — even more so than EAB.”
“Prolonged very cold temperatures can definitely kill off both EAB and the parasitoids, and the parasitoids appear to be less cold-hardy than the EAB themselves,” said Dr. Jonathan Lelito, another USDA researcher. Dr. Lelito went on to explain that even in extremely cold regions like northern Minnesota and parts of Canada, where a significant portion of EABs may have died because of the cold, the effect will not extirpate the species completely.
“Even with 50% mortality, the populations will recover in a few years or so and the infestation will continue on,” he said. “But biological control is a long game. Occasional setbacks will occur, and the populations of both hosts and parasitoids will tend to oscillate through time anyway. The long-term goal is the establishment of a balance, and severe weather events are just a step in the long march, so to speak.”
The same holds true for other insects. Once again: It’s complicated.
Article submitted by William A. Kolbe, BCE is a Board Certified Entomologist for Viking Pest Control based out of Warren, NJ. He has a Bachelor’s Degree in Entomology with a minor in Ecology from the University of Delaware. He is a member of The Denville NJ Community Gardens. He can be reached at 800-618-2847 or visit www.vikingpest.com
Reprinted with Permission from Richard Levine, Communications Program Manager at Entomological Society of America. Richard is editor and head writer of the Entomology Today Blog. Original article at: http://entomologytoday.org/2014/01/13/falling-temperatures-do-not-necessarily-mean-fewer-insects/