Issue 17, September 28, 2009

Soybean Aphid

Large numbers of "gnats" in the air in northern and central Illinois are soybean aphids, Aphis glycines. High infestations are present this year as far south as Interstate 70. Close examination will reveal a one-sixteenth inch long insect with a translucent green abdomen, black head and thorax, black antennae, and large oval transparent wings.

When aphids land on something, they probe it with their sucking mouthparts to see if it is good to eat. People with sensitive skin may feel a slight prick, but it is unlikely to leave a mark. Others are unlikely to feel anything at all.

These insects are migrating from soybean to buckthorn to lay eggs for the winter. Although this migration occurs over a six-week period, heavy migration typically lasts for one to two weeks. Control efforts against these winged migrants are not practical, nor recommended.

Soybean aphids pass through 15-18 generations during the summer on soybean, where they feed on the sap of the soybean plant. They live on the leaflet undersides as similar-sized, yellow to cream insects. At the end of summer, they migrate to buckthorn. Buckthorn, Rhamnus spp., is a glossy-leaved, thorny shrub common along the edge of forests and in disturbed areas such as fencerows and along streams. On buckthorn, these migrants give birth to another generation of females that mate with arriving, winged males. They then lay overwintering eggs on buckthorn. These eggs will hatch in the spring, the aphids will complete a couple of generations on buckthorn, and then fly to soybean for the summer.--Phil Nixon

Phil Nixon

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