I received my first seed catalog over the weekend. I am not sure, but I think they get a day or two earlier every year. Maybe they are trying to get in on the Christmas spending spree. Anyway, while I was looking at the catalog and thinking about plants, my mind wandered over to the pest side of things, and I thought I would see how cold it has to get to kill bugs.
My findings were not as joyous as I had hoped. I have always thought a cold winter meant fewer garden pest the following growing season. In fact, the thought of diminished bugs sustained me through some cold spells Mid-Missourians are inclined to suffer through — those of us who don't head to warmer climates, that is.
If you are counting on a bitterly cold winter to knock back insect pests and reduce the damage they'll do to your garden this summer, you may be disappointed. I found you could loosely divide them into three categories: those that run, those that hide and those that fight the cold.
They avoid cold weather by simply migrating to a warmer climate in the south, even all the way to Mexico and then return after winter. Monarch butterflies are famous for this, but other butterflies, moths and dragonflies do it as well.
Some "hiders" bury themselves in the soil or in leaf piles. Others may seek out crevices in trees, burrow beneath tree bark or under rocks or find warmth inside our garage, walls or house. Mosquitoes love to hide in places like moist leaf debris, and they thrive in environments ranging from the equator to the Arctic. A little deep freeze is unlikely to do them lasting damage. A freeze will kill some of the population, but it's not going to wipe all the mosquitoes out, so when temperatures rise a little and it rains, they'll be back.
Spider mites also bury themselves in leaf debris or ground litter. They can do damage even in the winter and are ready to do even more damage in the spring.
Ants head deeper into the ground to just below the frost line, where their large numbers and stored food keep them comfortable until spring arrives. Cockroaches (along with fleas, silverfish and spiders) will invade homes or compost piles. Wasps, ladybugs and stink bugs are all considered invasive pests in the fall and early winter because of their over-winter survival behavior like coming into your house.
Most bees and wasps hibernate during the colder months. In many species, only the queen survives the winter, emerging in spring to re-establish a colony. But honey bees remain active all winter long, despite the freezing temperatures and lack of flowers on feed on.
Insects that overwinter in the soil have a tendency to be less affected by winter weather conditions than those that don't. Insects that overwinter as eggs tend to withstand adverse conditions better than those that overwinter as adults, pupae or in the immature stage.
Since insect blood does not freeze at 32 degrees Fahrenheit, pretty much all insects can fight frost to some degree. Death by freezing isn't related to low temperature itself as much as it is the result of ice crystals forming in the body. Rapid formation and expansion of ice crystals cause cells to burst, resulting in organ and gut damage.
Some can actually survive being frozen solid. Although the ice crystals form inside the body, they do not damage the cells and organs of the animal. When the weather gets warmer, the crystals melt and the invertebrate becomes active again. Even in places such as Canada, where winter's night time temperatures often fall well below 0 degrees, insects survive.
Something else that effects insect populations is not the freezing temperatures during the winter but when spring arrives. When the temperature is at 40 degrees F or lower, they don't move. They move pretty slow around 45 degrees. If the temperature starts jumping to 70 degrees in mid-March or early April, insects get a fast start and quickly produce multiple generations that can quickly soar to hundreds of thousands. If, however, cold temperatures extend into April or even May, insects will miss one or more of their population cycles.
It looks like "garden sanitation" is really the key to reducing insects and diseases. Although I still think there are fewer bugs after a cold winter, maybe it is just because the springs that follow are cooler, too. Also, it is a little easier to survive the cold if I think it's helping the garden.
Peter Sutter is a lifelong gardening enthusiast and a participant in the University of Missouri Extension's Master Gardener program. Gardening questions can be sent to [email protected]
Editor's note: This is a reprinted columnn originally published in December 2016.