Binodoxys communis Field Cage Releases for Control of Soybean Aphid in Wisconsin

Dave Hogg & Dan Mahr-Department of Entomology UW-Madison

On Friday, August 10th 2007, 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 (Columbia Co.) and on a private farm near Deerfield (Dane Co.).

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 US Department of Agriculture as well as six Midwest states. These 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. 

Healthy soybean aphid (Photo: UW Madison Entomology Dept)

Soybean aphid “mummy”.

This aphid was parasitized, and killed, by the parasitic wasp Binodoxys communis.

(Photo: Dan Mahr, UW Madison Entomology Dept)

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. Access to the cage was provided by a zipper that ran lengthwise along the top of the cage. 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.

We then placed potted soybean plants containing soybean aphids and Binodoxys mummies from our laboratory colony into the cage, with the pot buried in the soil. Adult parasitoids were introduced directly through the zippered opening in the cage. We intend to leave the cages on for 10 to 14 days, which will be sufficient for the parasitoid to complete a generation, after which the cages will be removed to allow the parasitoids to disperse freely.

At the Arlington site, the release was made in a soybean field near the experiment station headquarters.  This field was planted late (mid June) and was 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.  Soybean aphid numbers were 150-200 per plant, most of which were the “summer/white” morph.  Approximately 100 mummies were released in the cage.

Binodoxys were provided to our project by Dr. George Heimpel of the University of Minnesota, 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 releases in Minnesota and has provided Binodoxys to collaborating researchers in IL, IN, IA, and SD for release this summer. We will determine the parasitoid's efficacy and spread, and it's survival over the winter into 2008.

This project is supported, in part, by the North Central Soybean Research Program.