Insects shrug off hot or cold winters

Cold weather won't necessarily a reduce insect populations the following summer.

Date published: 1/25/2013

http://fredericksburg.com/News/FLS/2013/012013/01252013/750341

WELL, winter has finally arrived. Subfreezing temperatures have settled in for at least a week or two. Many will find comfort in this blast of arctic air, believing that the cold temperatures will kill many insects that plague us throughout the spring and summer growing seasons.

While we might hope cold weather will limit the hordes of insects destroying our gardens or those that are merely a nuisance, most are not affected at all. In reality, I probably benefit more from warm winter weather than many of the insects that we fear.

Insects in our area are well-adapted to withstand even the coldest winters. Insects pass through life cycles of three stages (egg, nymph, adult) or four stages (egg, larva, pupa, adult).

Those that wait out the winter in the egg or pupa stages generally fare better during a cold winter than those that remain in the nymphal, larval or adult stages. Insects that overwinter in the nymphal, larval, or adult stages go into diapause, a kind of hibernation in which certain internal physiological changes take place to allow them to withstand cold temperatures.

The trigger for these insects to go into diapause is day length, rather than temperature. Once they are in diapause, they will not respond to warm periods during the winter. Many insects produce antifreeze compounds called cryoprotectants. Ethylene glycol, the same compound found in antifreeze for cars, is the most common cryoprotectant.

Though a warmer winter has a minimal effect on insect survival, the biggest advantage is to those insects that have more than one generation per year. Insects such as aphids, scale and mosquitoes can start breeding earlier than normal and will have more generations during the growing season. Those with only one generation per year, such as Japanese beetles, will be unaffected by the temperature of the winter.

Insect survival is also dependent on moisture, nutrition, species and other environmental factors such as snow cover. Insects that overwinter as adults search out protected sites such as behind bark in trees or in the leaf litter on the ground. Examples of these are boxelder bugs and lady beetles. They can also take it one step further and search out our homes to overwinter.

Another factor in successfully surviving the winter is the size of the insect. Larger insects such as grasshoppers are more susceptible to sub-freezing temperatures than smaller insects.

Probably the biggest factor in the survival rate of many insects is temperature fluctuation. Winters where temperatures remain cold will not have as great an effect on survival rates as winters that fluctuate between temperature extremes.

The bottom line is that you really can't generalize that we will have a bad year for insect pests because of a warmer than average winter.

By the way, ticks, which are not insects, overwinter on their warm-blooded host. If they fall to the ground during the winter, warmer temperatures will mean a greater survival rate.