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Over-winter insectsBy D. Bruce Bosley Extension Agent/Cropping Systems Colorado State University Extension I'm including a short version of an article Whitney Cranshaw, Colorado State Extension Entomologist has written on how insects overwinter. Contact me if you'd like the entire article. As cold weather moves into the state insects and mites undergo major changes to survive. Some species will die out over winter, those that annually re-colonize the state with spring and summer migrations (e.g., aster leafhopper, potato psyllid, black cutworm). Others prepare in several different ways. Caterpillars and beetles tend to burrow into soil or other protective cover. Aphids produce cold-resistant eggs that are attached to buds and needles. Several species like the protection that buildings and homes provide, producing seasonal nuisance problems. Regardless, most species that successfully overwinter undergo physiological changes as well. Insects become "cold-hardyat this time involving chemical changes including the production of antifreeze protecting their cells from lethal freezing. At this time, most insects are also in a condition known as diapause, a semi-dormant state where reproduction, development, and most feeding ceases. Diapause persists for months, and is only ended when certain environmental triggers are passed. Day length is sometimes used to determine when diapause occurs; a critical exposure to chilling temperatures may also be required to end diapause. Most Colorado butterflies spend the winter as pupae, in sheltered corners often several yards from the plants on which that the caterpillar stage earlier fed. However, a few manage to tough it out as adult butterflies, notably the Mourning Cloak, which may even be sometimes seen flying during warm days in winter. Several butterflies, including the Monarch, Painted Lady, and Variegated Fritillary migrate out of Colorado. The Monarch overwinters in the butterfly stage in the highlands of Mexico. Cutworms typically spend the winter as small caterpillars which resume feeding and growing as young plants sprout in spring. A few cutworms overwinter as eggs, which hatch in early spring. Ants and honey bees are social insects that maintain a colony from year to year. Underground nesting is the norm for ants, although some nest in wood or around homes. Almost all honey bee colonies are in maintained hives, although a few wild colonies occur in hollow trees, hollows of walls, and other protected sites. Overwintering stages are workers and a single queen. Egg laying is suspended in fall and begins to again during late winter. Yellowjackets and hornets are social insects that abandon the nest at the end of the season and start a new colony each spring. Overwintering stage is a fertilized queen which hides in protected sites such as under bark, around buildings, and other locations. Lady beetles overwinter in the adult stage, typically seeking protected locations (e.g, under clapboards, leaves, bark flaps) in the general vicinity of where they spent the summer. In particularly good sites, they often will winter in clusters. One species that recently established in the state, the multicolored Asian lady beetle, frequently winters in homes. Most aphids overwinter as eggs on some tree or shrubs. Some aphids, notably the Russian wheat aphid, overwinter on the plant on which they feed, continuing to feed and develop throughout winter as long as temperatures permit. Other aphids, such as the cotton aphid and greenbug, rarely survive Colorado winters and most found during the summer originate as annual migrants from more southern areas. Please contact me about this article or other cropping systems or natural resource topics at 522-3200, extension 285 in Sterling or 542-3540 in Fort Morgan. Date: 10/24/07
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