Binodoxys communis Field Cage Releases for Control of Soybean Aphid - Summer 2007

Binodoxys communis, an aphid parasitoid, emerging from a parasitized aphid. Photo credit: University of Minnesota

Binodoxys communis is a tiny parasitic wasp, one of the most important groups of natural enemies of aphids. There are nearly always parasitic wasps in the native range of an aphid species. In many cases when exotic pest species invade a new area, their natural enemies are left behind in their native habitat. Such was the case when soybean aphid invaded Wisconsin in 2000.

Midwest researchers have traveled to Asia, native home of the soybean aphid, and have identified several natural enemies that have the potential for biological control without themselves causing problems. Binodoxys is one such natural enemy of soybean aphid and has been approved by for field release by the U.S. Department of Agriculture as well as six Midwest states. This summer, the wasp was released in field cages in Illinois, Indiana, Iowa, Michigan, Minnesota, South Dakota and Wisconsin. The releases represent a milestone towards our long-term goal of introducing parasitoids that survive and reproduce in the Midwest and hold down aphid numbers from year-to-year with no further inputs.

Binodoxys communis is barely visible to the naked eye – smaller than a pinhead. The free-living adult wasp parasitizes the aphid by first laying an egg in it. When the egg hatches, the tiny larva begins to feed on the aphid until it is fully grown. Parasitized aphids often become inflated as the parasite reaches full size. The next generation wasp will emerge from the host aphid, and when it flies away, just the inflated shell of the host aphid remains; this is referred to as a "mummy". Each adult female wasp lays eggs in many aphids.

Researchers look for mummies, the darker brown objects on the soybean leaf shown above, to gauge the effectiveness of the beneficial insect in controlling soybean aphids. The light green spots on the soybean leaf are soybean aphids. Photo credit: David Hansen, University of Minnesota, from the Just for Growers website

Field Releases in Minnesota — In mid-July 2007, releases of the parasitic wasp were made in cages in research fields at the University of Minnesota St. Paul campus, on growers' fields and other research sites around the state. The cages confine the aphids and parasitoids. When new parasitoids emerged in 10-12 days, cages were removed and parasitoids allowed to attack aphids in the field. Since then, researchers have been monitoring the parasitoid's efficacy and spread, and will be monitoring it's survival over the winter into 2008.

Dr. George Heimpel, from the Unversity of Minnesota, was part of the team who collected the parasitoid in its native habitat and has conducted much research on the biology and safety of this natural enemy. Dr. Heimpel has made field releases in Minnesota and has provided Binodoxys to collaborating researchers in IL, IN, IA, WI, and SD for release this summer.

University of Minnesota entomologists George Heimpel (right) and Dave Ragsdale with one of the release cages. Photo credit: David Hansen, University of Minnesota from Just for Growers website

Field Releases in Illinois took place in late July 2007 in northern Mercer County as well as DeKalb and Champaign counties. Aphid density in the Mercer County field increased quickly at that time to an average of 287 aphids per plant on July 30, so the first release of the parasitoids was on July 30. Parasitized aphids ("mummies") from Dr. David Voegtlin's lab at the Illinois Natural History Survey, were placed inside a field cage over about 30 soybean plants infested with soybean aphids, and the cage was closed to keep out predators and allow the aphid population to build inside the cage.

In Wisconsin, releases of the soybean aphid parasitoid Binodoxys communis were made on Friday, August 10 in field cages on the UW Arlington Agricultural Research Station (Columbia Co.) and on a private farm near Deerfield (Dane Co).

At the release sites, a quonset hut-shaped field cage approximately 6 x 3 feet consisting of saran screen was placed over a row of soybean plants. Other aphid natural enemies (such as lady beetles and minute pirate bugs) were removed from the plants prior to placing the cage over them. The reason for doing this was to allow Binodoxys free access to aphids with interference or competition from other predators.

The field at the Arlington site was planted late (mid June) in the R2 stage of development. Soybean aphid numbers were 100-150 per plant, most of which were the “summer/white” morph. Approximately 85 mummies and 15 adults were released in the cage. At Deerfield, the release was made into a field that was in the R4/R5 stage of development with a similar aphid population.

An aphid mummy that was parasitized by Binodoxys communis. Photo credit: Dan Mahr, University of Wisconsin

Summary

The results of the multi-state releases are promising. We have been able to obtain release permits for 7 states and successfully shipped aphids for releases in all states. We have refined release protocols and made releases in 37 locations in cooperation with local farmers and university and state agricultural institutions. We have shown that B. communis reproduces in soybean fields in the Midwest and that they disperse from release sites. Furthermore, we have shown that they can be carried to new locations by winged soybean aphids. We have identified critical research questions (e.g., whether the parasitoid overwinters on buckthorn) and are committed to further research and applications in 2008.

Sources and Press Releases

U of M Field Testing Good Insects to Battle Soybean Aphids - press release from 7/18/07 (PDF)

Frequently Asked Questions about using beneficial insects to control soybean aphids (PDF)

Soybean Aphid Biocontrol - An Exotic Approach. RAMP newsletter May 2007

Soybean Aphids Attract Attention in Several Areas of Illinois, The Bulletin, August 3, 2007

Binodoxys communis Field Cage Releases for Control of Soybean Aphid in Wisconsin Wisconsin Crop Manager, August 16, 2007

Attack Of The Aphid-Eaters. Corn and Soybean Digest, August 1, 2007.