WICHE: All this cold could be good

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Will the ‘polar vortex’ hurt invasive insects or kill pesky ticks?

By Jeneen Wiche

A few weeks ago on Ira Flatow’s Science Friday there was an interview with research biologist Rob Venette from the U.S. Forest Service in Minnesota who addressed the effect temperature has on certain insects.

The ability of insects to survive winter – when so many of them thrive in summer – has always fascinated me. While we would most certainly root for the bees and butterflies, my enthusiasm would wane for fleas and ticks.

Venette and his colleagues are specifically researching the emerald ash borer and sub-zero temperatures. The emerald ash borer has killed an estimated 50 million ash trees in North America – including in Shelby County – and has a range as far-reaching as Colorado to the west, Georgia to the south, and up the eastern seaboard into Quebec and Ontario. It has been detected in 21 states, including Kentucky and Indiana.

The research indicates that Minnesota’s -24 degrees could kill the immature emerald ash borer that winters just beneath the tree’s bark by up to 50 percent. And -30 could have a kill success rate of 90 percent.

This is good news to a state that has black ash-dominated forests. Further, the amount of time that the insect needs to be exposed to these killing temperatures is calculated in minutes so it doesn’t have to be sustained for days!

Kentucky and Indiana also are plagued with the emerald ash borer we have not seen actual air temperatures that low and the wind chill only makes it less bearable for us not the cold blooded insect in hibernation or diapause. The thrifty tick, after finding a winter haven underneath some warm leaf debris, can slow their functions down so a minimal amount of energy is needed to maintain bodily functions during hibernation. Venette explained that ticks begin to freeze at 7 to 14 degrees, depending on the species, but they can offset this vulnerability by seeking refuge under leaf debris that can naturally maintain a near 28.

Think about all those insects that lurk under the wood pile as they seek shelter from the vortex! So, the “silver-lining” of the “Polar Vortex,” if there is one, is that is may slow the progress of the emerald ash borer in the northern hinterlands; and it may snagged few ticks in Kentuckiana.

The good news, according to Venette, is that beneficial insects usually fare well in the cold as they have other mechanisms to survive. Honey bees, for example, will shiver to radiate heat as the huddle around their Queen. Apparently a healthy colony can warm the hive to 90 degrees. Amazing.

Some insects are considered “freeze tolerant” which is actualized through a process called diapause.

Insects that practice diapause completely shut down during the winter. Like some spring bulbs, they also have to go through a period of dormancy triggered by cold temperatures before they can actually awaken again once spring arrives. This survival mechanism, then, would only work for insects that live in certain climates.

Insects need to find appropriate protection for the winter, wherever that may be, but in order to survive around here they still need to lower the water content of their little insect bodies.

Purdue entomologist Tom Turpin: “Winterizing for an insect is much like the process we go through to winterize a car. We add anti-freeze to the car. Insects add anti-freeze to themselves. If the liquid in the cooling system of a motor is allowed to freeze, the expansion during the process will break the radiator and hoses. The same is true of the liquid in insects. If it is allowed to freeze, the crystals that form will destroy the cells and tissues of the insect and cause death.”

In fact, the compounds that make up car antifreeze and insect antifreeze are very similar. Automobile anti-freeze has glycol in it; insect anti-freeze has glycerol. The compound effectively drops the freezing point of the liquid.

This means that the insects little system is shut down for the winter with low moisture content so it won’t burst like a frozen pipe. Once an insect has converted its liquid to glycerol it can withstand temperatures below freezing but severe winters may still see a higher insect mortality rate.

We shall see.


Check out gardening columnist Jeneen Wiche’s work at www.SwallowRailFarm.com. You can find her columns also at www.SentinelNews.com/agriculture. She answers questions once a month in SentinelNewsPlus. To submit a question, send an E-mail to jwiche@shelbybb.netand type “Sentinel-News” in the subject field.