Soybean Aphid

Aphis glycines

Soybean aphids on the underside of a soybean leaf
Soybean aphids on the underside of a soybean leaf. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
As their name suggests, these tiny insects are a pest of soybeans. Due to their very short generation time (2-3 days), the population within a field can increase dramatically in a very short time.
Soybean aphids are very small (up to 1/16") and yellow/green in appearance. They are often found on the underside of leaves, although they may be present on any part of the plant.
Close-up of soybean aphids on a soybean leaf
Close-up of soybean aphids on a soybean leaf. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
Soybean aphids suck the plant juices of their host plant, weakening it. Yield losses are often compounded in fields which are under other forms of stress as well, such as drought stress. Because of their ability to reproduce rapidly, losses of 10% or more are not uncommon.
Insecticides are available for treating soybean aphids. The number of aphids present and the growth stage of the plant should be considered before deciding to apply insecticides, since applying insecticides can kill beneficials and exacerbate other pest problems, particularly spider mites. Always read and follow all label instructions.