Cold, Glorious Cold: How Cold Snaps Play a Role in Managing Invasive Species

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Invasive species like the emerald ash borer are not always equipped to handle extreme and prolonged cold. Image courtesy of USDA

Invasive species like the emerald ash borer are not always equipped to handle extreme and prolonged cold. Image courtesy of USDA

When the temperatures are so chilly that you can’t step outside without losing your breath to the frigid air, it seems like the cold has very few redeeming qualities. However, cold does play an ecological role.

For some plants, a period of winter cold followed by heat and light triggers new growth in the spring. To some degree, cold can also help manage the pests that prey on plants. Some invasive insects may not be able to survive our continent’s intense cold snaps.

Pest Problems and Winter Weather

Why do we need to control insect populations? Many insects are herbivores, and they love to eat trees and other plants. Drought and hot summer temperatures can stress trees out, making them more susceptible to a large-scale insect invasion.

While cold winter temperatures have historically kept insect populations in check, with warmer winter temperatures and a lack of cold snaps even native species may get a foothold in a plant population, using the dual opportunities of warmer weather and stressed vegetation to expand their range. Invasive insect species can also lack natural predators, making it even easier for them to gorge on local plants.

How Animals Handle the Cold

Plants have an ally in the winter cold snap. Winter’s cold changes animals’ behavior, and it also acts as a natural control for some animal populations. For animals, very cold winter weather can be dangerous. As water freezes, it expands. Since animals contain water, if their cells freeze they can burst, causing damage to the animal’s body if it’s exposed to extreme cold.

Animals have a variety of responses to winter weather. Some migrate before extreme weather hits. The monarch butterfly is a good example of a migratory insect. Other animals migrate locally. For example, worms may burrow below the freezing ground or move closer to warm spots if they are near a building. Some animals try to tough out the winter weather using fur, feather, fat or natural antifreeze.

How Insects Deal With Freezing Temperatures

Amazingly, many insects can survive a freeze using their own internal antifreeze: ethylene glycol. Similar to the antifreeze that you put in your car, this internal antifreeze allows animals’ cells to be exposed to temperatures much lower than those that would normally cause ice to form.

If the insects are susceptible to freezing, this antifreeze or cryoprotectant allows insects to survive in weather that’s much colder than they would otherwise be able to handle.  However, freeze-susceptible insects do tend to have a point at which they will freeze, especially if they are exposed to the cold for long periods of time.

Other insects have varying degrees of cold-tolerance. Some may be able to survive freezing, as the liquid around their cells freezes, but not the cells themselves. They might not look lively when it’s 30 below, but when the temperature rises, they perk up.

In part, the insects’ adaptations depend on their genetic histories. If the bug came from a climate that experiences extreme cold for several days at a time, they may do just fine in prolonged cold weather. If they come from a climate that’s a little warmer than North America and one that doesn’t usually experience extreme cold, they may die. The longer the cold weather lasts, the more challenging it tends to be for the insects.

Cold Snaps Can Help Control Insect Populations

Scientists studying the populations of native and invasive insects are watching closely to see what impact the most recent cold snap might have on the populations of these insects. Will it dampen their spread, or will populations spring back? In part, this depends on each species’ cold tolerance.

Some species may not survive the cold temperatures. The hemlock woolly adelgid, for example, hails from Japan, and its body forms ice crystals around -5 F. Other invasive species are well-suited to the cold. In Ontario, scientists studying the Asian long-horned beetle have determined that the beetle may be freeze-tolerant. It contains glycol, and it can experience extreme cold of -40 F and then come back to reproduce.

In areas impacted by the Mountain Pine Beetle, the timing of the cold snap may be a little late. Sudden cold weather can kill pine beetle larvae that overwinter in the bark of the trees. This is particularly true in the fall, when the smaller, weaker larvae, pupae, and eggs can succumb when temperatures stay below -13 F for several days. Since the beetle larvae grow throughout the winter, temperatures have to get down to -31 F for the larvae to die in the winter months.

Winter Weather and Invasive Species

Prolonged and extreme cold can be a challenge for many animals, even those that naturally live in an area. For introduced species and species that have expanded their range northward, the cold snap may provide a natural check to population growth. This spring and summer’s thaw will reveal what species had the ability to survive the freeze – and which ones did not.

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© Copyright 2014 Tricia Edgar, All rights Reserved. Written For: Decoded Science
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