Predictions for this year’s winter weather have started rolling in and so far, signs point to lower than average temperatures and higher than average snowfall. That means that we should have less insect pests to deal with in 2017, right? Well, it’s not quite that simple.
Insects are remarkably adaptable and live on every single continent including Antarctica. While insects are exothermic or “cold-blooded” and unable to produce their own body heat, they have developed a number of ways to survive in cold weather.
Some insects migrate to warmer climates to completely avoid the cold. One of the most famous examples of insect migration is that of the monarch butterfly. Monarch populations in the eastern United States migrate south to spend the winter in Mexico before reproducing next spring. Successive generations make their way back up north and start the cycle all over again.
Many pest species also take advantage of migration, but in a different way. Pests like earworms, cutworms, and leafhoppers die off during winter in Ohio only to have their populations replenished in the spring by northern migration from in the warmer southern states where winter survival is easier.
Other insects have found ways to survive in Ohio all year round. One such strategy used by insects like ladybugs, cluster flies, and some species of mosquitoes is to seek shelter in hollow logs, leaf litter, tree bark, and even inside buildings. Honey bees will spend the cold weather warm in their hive. They stay in a protective huddle around the queen, generating heat by beating their wings.
Not all insects overwinter as adults though; they can also survive as an egg, larva, or pupa. Winter conditions are a bit too harsh for adult praying mantises but their protected egg cases make it through just fine. The larval stage is used by corn borers that shelter in the base of corn stalks and by many beetle species that spend it underground in the soil. Certain species of moths and butterflies will spend the winter in their pupa form, tucked away in a chrysalis or cocoon.
Temperatures can still get very low no matter how well sheltered an insect is. This is where the really impressive cold weather adaptations come in. Insects have the ability to enter a state called diapause where they are essentially in suspended animation. Entering diapause slows the insect’s metabolism and growth to an almost complete standstill, allowing them to go without eating, drinking, or moving.
To cope with sub-zero temperatures, some insects can produce fluids within their bodies that act like antifreeze. Certain insects are even able to live through being frozen — not something any human could ever do.
That brings us back to the original question: does a cold winter mean less insect pests the following year? Despite all of their adaptations, insects can still only take so much. The duration, intensity, and variability of cold weather can all impact winter insect survival rates.
Take the soybean aphid as an example. Soybean aphid eggs can survive in temperatures to about -29 degrees F, though only for short durations. A harsh winter can additionally impact pest populations by killing off their beneficial insect predators. The parasitoid wasps that prey on emerald ash borers are more susceptible to the cold than the emerald ash borers themselves.
Having a warm winter is no guarantee of a large insect population either as several other factors influence survival rates. Precipitation, humidity, late season cold snaps, and food availability can all have a significant impact. If warmer than average temperatures coax agricultural pests out of hiding before crops have been planted in the spring, there won’t be anything for those insects to eat.
As an environmental scientist, I can’t finish this article without reminding you that not all insects are bad. Insects help pollinate our crops, clean up decaying animal and plant matter, control pest populations, and provide food for other animals. Even if you are not the biggest fan of insects, I hope you’ve gained some appreciation for just what adaptable creatures they are.
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Rebecca Longsmith is Resource Conservationist for the Delaware Soil & Water Conservation District.