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The Garden Plot for January 04, 2008
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: "Insect Winter Survival"
Gardeners smile smugly when it gets really cold in December and January. We like to think the cold is natures’ way of giving us a leg up on insect pests next spring. But does a harsh winter always mean lower insect populations the following season? Not necessarily. Many insects have developed ways to survive long, cold winters.
One of the most common ways is to spend the winter as eggs. Eggs are able to outlast winter’s hardships with thick shells that protect them from cold temperature and moisture. Some eggs even have an extra layer of hair or foamy froth that provide added insulation. Tent caterpillars spend the winter as super-insulated eggs, in a frothy cylinder attached to branches of the plants they’ll feed on next spring.
Some insects go into a kind of “suspended animation”, a resting state called diapause in which they use very little energy. These insects spend the winter in protected places, beneath mulches and plant debris, under the soil, burrowed into wood, under rocks, and within the walls of our homes. Many root weevils spend the winter as adults in the soil beneath the plants they’ll attack next spring. Some insects, like Elm leaf beetles and Box Elder bugs, are a nuisance in their semi-resting winter survival mode; they crawl around very slowly inside our houses.
Other insects spend the winter as immature “pre-adult” forms, such as larvae, pupa, or nymphs. Tomato hornworms defy cold temperatures by heading into the soil and spending winter as a pupa, or cocoon.
There are even insects that avoid winter altogether by migrating to warmer climates. Just like “snowbirds”, Corn ear worm moths fly many, many miles back up to Montana each spring, rather than freezing their antennae off in a real Montana winter.
So, that’s why insects can survive even frigid winters. They’ve adapted creative ways to cope with cold temperatures. But what about Chinooks, those mid-winter thaws during which the weather warms up to spring-like temperatures only to drop precipitously within days or weeks? Insects are not so easily fooled by mid-winter thaws. Most insects are cued into day length. They get the message that spring is coming from longer days and shorter nights. In other words, they are more attuned to day length than to temperature.
What plays havoc with insect survival, is cold temperatures in late winter or early spring, when insects are coming out of their resting periods and those thick insect egg shells are starting to get thinner with the approach of longer days. One way to decrease insect populations is to expose them to cold at this time when they are finishing up their winter rest periods. For example, insects that spend the winter as adults in protected areas suffer when, in late winter, you remove the mulches and covers beneath which they are hiding. A good example is the weevil that kills the very top branch, or terminal, of spruce trees. This weevil spends the winter in fallen needles below spruce trees. Raking away the needles in late winter exposes weevils to cold temperatures when they are most vulnerable. That’s when a gardener can smile smugly about the cold.
Helen Atthowe's new short program of gardening tips
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