These cryoprotectants are effective as long as the insect body cools gradually (i.e., the insect acclimates to the cold, as in the fall, triggering the production of the compounds) and until temperatures get really cold (beyond the freezing point of the antifreeze). Examples of cryoprotectants are the sugars trehalose and mannitol, or the sugar alcohol glycerol (we humans use glycerol as an antifreeze in industrial processes). The antifreeze is composed of specialized carbohydrates (in a fancy term, “cryoprotectants”) that lower the freezing point of the body fluid, preventing the formation of ice crystals. Other insects are freeze avoidant-they accumulate antifreeze in their cells prior to the winter. Some insects are freeze-tolerant-they actually survive the formation of ice crystals in their body by producing ice nucleating proteins that “control” the freezing process. Rapid formation and expansion of ice crystals cause cells to burst, resulting in organ and gut damage. Death by freezing isn’t so much related to low temperature itself as it is the result of ice crystals forming in the body. Insects that do overwinter in Michigan have ways to survive typical winter weather. Instead, populations continuously reproduce in southern states, and insects move north with spring weather fronts to recolonize northern states. Pest insects such as armyworms, earworms, potato leafhoppers and some grain aphids do not survive the winter in Michigan either. Eventually, the children or grandchildren of last year’s monarchs return to Michigan. In the spring, the monarch population makes its way back north. The classic example of this is the monarch butterfly, which migrates south in the fall to overwintering sites in Mexico. The first strategy is to avoid freezing conditions altogether. In order to survive and thrive in climates such as ours, insects have developed several ways to deal with cold weather. Insects are exothermic (cold-blooded), which means they cannot produce their own body heat. Freezing temperatures are detrimental to many forms of life, including most insects.
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