Low Soybean Aphid Numbers Predicted in 2008

Soybean aphid populations could be exceptionally low next spring, based on the number of soybean aphids found in suction traps this past summer and fall.   Researchers are predicting low numbers of the soybean aphid in 2008 because so few of the insects were found in checkoff-funded suction traps over a wide region of the Midwest.

Started in 2001 in Illinois, the suction trap network has 40-plus traps spread throughout 10 states of the north central U.S. soybean-growing region -- Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Missouri, Minnesota, South Dakota, and Wisconsin. The suction trap network collects soybean aphids as they migrate from soybean fields in the late summer and fall to woodlands and field edges where the insects lay eggs that overwinter on buckthorn.

David Ragsdale, University of Minnesota entomology professor, is principal investigator in a multi-year research project that has as one of its objectives to determine if the numbers of soybean aphids captured in the suction trap network correlate with populations found in soybean fields. Ragsdale and his co-investigators at other universities, particularly David Voegtlin at the Illinois Natural History Survey who manages the trapping network, have found that the September and October 2007 trap catch of soybean aphids is the lowest number ever recorded in the study. Also, no soybean aphids were found on buckthorn, a further indication that 2008 should be a light aphid infestation year.

The seven-year study is showing a consistent correlation between soybean aphids trapped in the fall and aphid populations scouted the next spring. High numbers of soybean aphids found in the fall correlate to a greater population of aphids the following spring.  

To view suction trap capture data which is posted weekly June to November, visit www.ncipmc.org/traps/index.cfm.

Efforts to find biological controls for the soybean aphid, a native of Asia, have resulted in the release of a natural predator.  A parasitic wasp from China, Binodoxys communis, was cleared by the USDA-Animal Plant Health Inspection Service and released in seven states during the 2007 growing season.

Binodoxys is a small wasp that attacks soybean aphids and lays eggs within them. The eggs hatch inside the aphids, feed on them, and emerge from the aphids as an adult wasp. In Asia, several species of wasp parasitize soybean aphids at a different life stage of the aphid, and may be responsible for keeping soybean aphid populations under control.

George Heimpel, a University of Minnesota entomology professor, and students have conducted the laboratory rearing of Binodoxys communis in Minnesota. The wasp was studied to make sure that it did not attack any other aphid species. Researchers in Minnesota and USDA scientists Kim Hoelmer and Keith Hopper in Delaware currently have 11 different species of parasitic wasps in quarantine and multiple strains of each species, each originating from different parts of Asia. Federal regulatory review requires extensive host specificity testing and several species have already been ruled out because their host range, or the number of hosts they will attack, was too broad.

Two species of parasitoids, Aphelinus varipes and Aphelinus mali, have also shown narrow host ranges and may be safe for release. The species are currently under study at the USDA-ARS Beneficial Insect Introductions Research Unit at Newark, Del.

Researchers are monitoring the release of Binodoxys communis and are hopeful that the wasp will prove to be successful in establishing itself here. Next spring, entomologists will search for evidence that the wasps released in 2007 survived the winter in the upper Midwest. If the wasp can demonstrate it is efficient and effective in parasitizing soybean aphids, Ragsdale and other entomologists will embark on a mass rearing of Binodoxys communis.

It will probably be several years before researchers determine if the release of Binodoxys communis is making a noticeable difference in the control of soybean aphids. If the small wasp is established successfully, it will help lower soybean aphid populations and reduce the severity of damage to soybean yields.   

The soybean checkoff, funded by U.S. soybean producers, has provided a major source of funding to study soybean aphids and biological controls for this major soybean pest. The soybean checkoff provides at least 50 percent of the funding in a shared partnership between researchers and soybean growers.

Grower dollars at the state and regional level are paired with USDA and university funding for further research in biological control and management of soybean aphids.  The North Central Soybean Research Program, funded by the soybean checkoff, is leading efforts in soybean aphid research and other plant health initiatives.




©2007 NCSRP