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The Insects of Fall

By John Pohly, Colorado State University Cooperative Extension agent, horticulture

Nights are growing cooler, the days are growing shorter and some sticky material is showing up on leaves of your maple trees.

The sticky material is honeydew, a sweet liquid that aphids secrete. In early autumn aphid predators, such as lady bug beetles, begin to prepare for winter. Some beetle species fly to the mountains to overwinter at elevations typically above 9,000 feet. As these predators leave areas, where they have been feeding on aphids, the number of aphids -- and the amount of their honeydew -- increases.

So much honeydew can accumulate that leaves will glisten with the liquid. If you park your car under an aphid-infested tree, the car will end up speckled with clear little droplets of honeydew which are difficult to wash off. It's a sugary substance, however, that soap, hot water and a little elbow grease should take care of.

In addition to increased aphid activity, you may notice other changes in insect behavior with the coming of autumn.

Butterfly larvae soon will stop feeding on plants and turn into pupae, which is their resting form before becoming adults. These pupae will spend the winter in sheltered areas. While in the pupal stage, the larvae will change into adult butterflies which will emerge in the spring.

Even the tomato hornworm will turn into a pupae, buried several inches deep in the soil for protection from the cold. In the spring the sphinx moth adult will emerge from the pupa in place of the hornworm.

Cutworms typically spend the winter as partially grown caterpillars, which may find shelter in the ground or in fallen leaves. You may notice them when cleaning garden debris in the fall. They will resume feeding and growing as young plants sprout in spring.

Yellow jackets have been working all summer to build large colonies. They often are found feeding on honeydew produced by the aphids. They abandon their nests at the end of the season when freezing weather arrives. Most of the worker bees die off over the winter, but the fertilized queen often survives and hides in protected sites such as under bark, around buildings and other locations. In spring, surviving females attempt to individually establish new colonies.

Flies tend to seek warm locations as the days and nights become cooler. Often, they become real pests in the home as they seek the warmth of the house. In the house they will find cracks or other hiding places to pass the winter in a semi-dormant state. While overwintering they will neither feed nor reproduce.

Spiders produce a silk-covered mass of eggs in the fall and then die. The eggs that survive the winter will hatch next year.

Along with cooler temperatures, you might find bugs, such elm leaf beetles, boxelder bugs and stink bugs, looking for shelter in your home. Some folks have such heavy infestations, that they've cut down host trees to eliminate the pest. A female box elder tree, for example, will attract box elder bugs. Getting rid of the tree may be an attractive alternative to doing battle with the insects.

Photos of aphids: Judy Sedbrook

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Date last revised: 01/05/2010