By Judy Sedbrook, master gardener, Colorado State University Cooperative Extension, Denver County
Aphids are very common. Sometimes called plant lice, they are small, soft-bodied, pear-shaped insects, generally less than 1/8" long. Most are green or black but they can also be found in a variety of other colors as well. A characteristic common to all aphids is the presence of cornicles, or tubes, on the back ends of their bodies, sort of like "tailpipes". These cornicles secrete substances that help protect the aphids from predators. Over winter, aphids exist as eggs on perennial plants and hatch in the spring.
The insects cause injury to plants by sucking the sap and juices from the soft, new growth.This damages the host plant's ability to properly process food and causes the plant to lose vigor, wilt, distort or show spots. Aphids also can infect healthy plants with viral diseases they have picked up from unhealthy plants.
They often live in large clusters or colonies and are found together with ants. The ants feed on the honeydew produced by the aphids and protect the aphids in return, often keeping their eggs through the winter in their nests. In the spring, the ants transport the aphids to host plants and then protect them from enemies.
Aphid colony on rose
The honeydew is a sticky, sweet substance that is produced by the aphids when they can't use all of the sugar taken from plants. It can drip from infested trees or shrubs onto cars, sidewalks, and porches creating quite a mess. You may see a black, sooty mold growing on it.
Aphids are most likely to be a serious problem in situations where they are protected from their natural enemies: either in an enclosed area like a greenhouse, or when their natural enemies have been destroyed by insecticides.
Natural enemies play an important part in controlling aphids. Lady beetles, lacewings, damsel bugs, flower fly maggots, certain parasitic wasps, birds, and fungal diseases all attack aphids.
For more information on Aphids, see CSU Fact Sheet 5.511.
Photographs courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010