The best option for long-term control of the soybean aphid is the reestablishment of their natural enemies. The soybean aphid is only a sporadic pest in most of their native areas in  China, Japan and Korea because of the presence of parasitoids and predators that keep them in check. UW entomologists are studying natural enemies that occur in Wisconsin, as well as working towards the release of additional aphid parasitoids collected from their native areas.

The most common naturally-occurring soybean aphid parasitoid observed so far in Wisconsin is a wasp called Lysephlebus testaceipes. Soybean aphids parasitized by this wasp become tan mummies. These wasps seem to be increasing in Wisconsin since 2000, perhaps due to a shift in their host pattern towards the soybean aphid. Parasitism numbers in 2003 were estimated at about 1%. This is just a beginning of aphid control, as the amount of combined parasitism required to suppress aphids is considered to be around 20-30%.

Aphid mummies. Photo © Bob Ellingson Click on image to view larger version.

UW entomologists have released another aphid parasite called Aphelinus albipodus. This wasp was released in 2002 and 2003, with the goal of getting a critical mass of wasps into the environment so that they can form a self-sustaining population which can spread and increase on its own. This process will take several years. The wasps successfully attack soybean aphids in Wisconsin under typical field conditions. The question remains as to how well they survive Wisconsin winters, and investigations are in place to answer that question.

This summer, on August 10, releases of the soybean aphid parasitoid Binodoxys communis were made in field cages in southern Wisconsin. Sites of the releases were on the UW Arlington Agricultural Research Station and on the Kevin Shelley farm in Deerfield. The release marks the first introduction of an exotic natural enemy of the soybean aphid in the United States, and a milestone in the our efforts to establish a check-and-balance system to keep soybean aphid populations in check.

Consider the presence of natural predators such as lady beetle larvae and adults, and evidence of parasitized aphids when assessing soybean aphid treatment options and timing. When scouting, learn to recognize aphid mummies. The parasitoids (small female wasps) themselves are not easily seen, but the results of their work is - the aphid mummies. Parasitized aphids lose the healthy green-yellow color and gradually turn black, tan, pink or brown. Apids infected by fungi can have a fuzzy look. Wasp-parasitized mummies may be slightly bloated.

Contributed by Bob Ellingson, UW Entomology