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Insects and Winter
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First an update on the drought monitor is in order. Even with recent moisture, all but Northeast and part of North Central Kansas are in some stage of moisture deficit. Barton County is on the eastern edge of abnormally dry as is most of Rice County. Just to our northeast the deficit disappears. Moderate drought is as close as western Pawnee County and severe drought has settled over much of Southwest Kansas. This is hardly unusual for the western half of the state, however, damage to winter wheat due to cold is often tied to soil moisture deficits.
Today’s topic, “Insects and Winter,” is of interest as people noted seeing Asian lady beetles and other insects when it warmed up after having temperatures reach -15 degrees. First our temperate climate, having winter, does help mitigate insect problems compared to places like the Southeastern United States. As you recall from your school science class, insects are cold-blooded. They cannot regulate their internal body temperature like mammals and birds can. However, they have a variety of physiochemical adaptions to survive freezing temperatures.
• Insects have an ability termed diapause. In diapause, development and activity are suspended in response to adverse environmental conditions. The insect is in essence dormant to avoid heat, drought, or here cold. Environmental triggers cause this behavior to be initiated and to end. Diapause can occur during egg, immature, pupal, or adult stages. For the pupal and egg stages, metabolism is minimal while in adult and immature stages it may resemble what we think of as hibernation or they may feed and move but at a minimal rate. A very typical trigger to initiate and end diapause is the change in photoperiod, day length, as seasons change.
• If you noticed all the pretty butterflies in alfalfa fields last fall, they were laying eggs which will overwinter and hatch in the spring. An insect like Hessian fly larvae infesting wheat will travel to the crown of the plant and overwinter in the stems of tillers as pupa termed flaxseed. Army cutworm and several other moth caterpillar larvae survive in that stage over winter below the soil surface in fields of crops like wheat and canola here. They come out to feed at night or on cloudy days on canola and wheat that have broken dormancy. Some of the “pesky” adult insects such as the lady beetles, box elder bugs, and house flies find places to hang out and reappear during periods of warmth. Before we speak to insects surviving freezing temperatures, keep in mind many don’t. However there is survival in numbers. During mild winters more survive to inundate the environment more quickly. More severe winters hold back their numbers and the population grows more slowly until adults can reproduce.
• Briefly how do they survive the cold? First insects that burrow in the ground have an advantage and the deeper they burrow the better. Except during weather cold enough for the ground to freeze to several inches, insects in the soil, while cold, can stay above freezing. Next there is super-cooling. Here the insect changes physiologically and lowers the temperatures for its cells to freeze. Essentially making antifreeze for its cells. Finally, we have freezing tolerance where the cell contents actually freeze but the insect cells remain intact.