Plant Health Initiative

Field cages were set up in aphid-infested fields for release of the soybean aphid parasitoid, Binodoxys communis. Photo credit: University of Minnesota

NCSRP Soybean Aphid Biological Control project

NCSRP, along with state checkoff boards and the USDA, has invested in a huge biological control effort to keep aphid populations low. The goal is to identify how pests are controlled in their land of origin and bring those controls to our country. It’s a complicated process that takes years.

A parasitoid (which eats its prey from inside) first must be identified. Then researchers must prove that it will only attack the targeted pest. This strategy, called classical biological control, has been highly successful in agriculture. For example, the cereal leaf beetle and the alfalfa weevil, both non-native insects, are now effectively suppressed by biological control and rarely have to be managed by growers.

New natural enemies of the soybean aphid

The first challenge was to explore Asia for natural enemies of the soybean aphid that were missing in North America. Binodoxys communis was identified as a soybean aphid specialist. Because the permit to release Binodoxys was granted late in 2007, few releases were done that year, followed by more in 2008. In 2009, researchers followed up at those sites to check on survival and also do new releases.

An aphid parasitoid, Binodoxys communis adult Photo credit: Kelley Tilmon, South Dakota State University Read more about Bindoxys communis»

Because these are not mass releases but many inoculations, it may take years for Binodoxys to be established. Biological control will not eradicate the aphid, but will establish a new equilibrium between aphid and Binodoxys, thus managing the pest to a level where damage is minimal.

While efforts are ongoing to determine the success of Binodoxys as a tool to suppress the soybean aphid, researchers are looking further to determine the effectiveness of two new parasitoid wasps that may be better able to handle Midwest winters.

Combining biological control with host resistance

Another promising area of aphid control is host resistance. Soybean varieties with the first discovered resistance gene will be on the market in late 2009. This gene named Rag1, was discovered by University of Illinois scientists with funding from the Illinois Soybean Association and the United Soybean Board. A second gene, Rag 2 was also discovered in this research program. More resistant genes are on the way. Using resistant varieties, farmers may expect to see some aphids land and colonize, but the population will either not grow or will grow at a reduced rate, so spraying may be eliminated.

Researchers are hopeful that the combination of host plant resistance and new beneficial insects will keep aphid populations below treatment levels within the decade.

Steps to a successful introduction of beneficial insects 1.  Climate / Habitat Matching From 2001 to 2006, entomologists from University of Minnesota, the Illinois Natural History Survey, Purdue, and the USDA worked with Asian cooperators to identify suitable areas for collecting parasitoids. These areas had both soybean production and buckthorn, and were a climate match for important soybean production areas in the United States. Climate-matching increases the likelihood of finding insects adapted to local conditions, increasing the success of an introduction. 2.  Foreign Exploration The USDA Agricultural Research Service worked with scientists in China, South Korea, and Japan to collect natural enemies of soybean aphid. Parasitoid collections were made from both soybean and buckthorn, at different times of the year. These insects were shipped back to U.S. quarantine facilities. 3.  Importation It was an administrative and logistical challenge, requiring many permits, to move live insects from foreign countries to the United Sates. Parasitoids have a short life cycle; the insects must reach the U.S. from Asia in a matter of days, or die in transit. 4.  Rearing and Testing in Quarantine Back in the U.S., parasitoids were kept in quarantine at the USDA Beneficial Insect Research Lab in Delaware or at a new MAES/MDA Facility at the University of Minnesota in St. Paul. It is very labor intensive to rear plants and keep aphid colonies to rear the wasps. Each parasitoid is tested for how effective it is at using soybean aphids as a host. It is important not only to release an effective natural enemy, but also one with a narrow host range that will not disrupt non-target aphid species. 5.  Release Permits Once efficacy and host range data are complete, more permits are needed from the U.S. and Canadian governments to make field releases. Permits for the release of the first parasitoid, Binodoxys communis were finalized in the spring of 2007. 6.  Field Introductions The first field releases of Binodoxys was done in IA, ,IL, IN, MN, SD and WI in 2007 and in IA, IN, MN, MI, SD, and WI in 2008. Research entomologists are now determining the parasitoid's efficacy and spread, and it's survival over the winter.