Plant Health Initiative

NCSRP Soybean Aphid Importation Biological Control project

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

Importation biological control, also called classical biological control, of the soybean aphid is seen as a promising management option in North America.

The soybean aphid rarely attains pest status in its native Asia, and a number of studies in Asia indicated that both insect predators and parasitoids were instrumental in keeping densities below economically important levels. In particular, parasitism levels of the soybean aphid in China often exceed 10%, while they are typically far below 1% in North America.

These observations suggest that the absence of parasitoids may be an important contributing factor to the pest status of the soybean aphid in North America, and consequently that classical biological control using Asian parasitoids has the potential to suppress the soybean aphid below economically important levels.

The North Central Soybean Research Program, along with state checkoff boards and the USDA, has invested in a biological control effort to establish one or more aphid parasitoid species to attain long-term suppression of soybean aphid.

A major advantage of this form of biological control is that once it is established, it is free of charge to growers, making the cost/benefit ratio potentially very favorable.

Examples of successful importation biological control

Classical biological control has a long history in U.S. agriculture. Two notable examples are the cereal leaf beetle and the alfalfa weevil, both non-native insects, which are now effectively suppressed by biological control and rarely have to be managed by growers.

The goal is not to eradicate the aphid, but to establish a new equilibrium between the aphid and it's natural enemies, thus managing the pest to a level where damage is minimal.

An aphid parasitoid, Binodoxys communis adult Photo credit: Kelley Tilmon, South Dakota State University

A missing link: aphid parasitoids

The first challenge was to explore Asia for natural enemies of the soybean aphid that were missing in North America. Because parasitic wasps play such an important role in suppressing the soybean aphid in Asia, and are largely missing in the U.S., several promising species were brought to this country and put through a series of safety tests. The identification, testing, and release of a new biological control organism is a complicated process that takes years.

The first aphid parasitoid to be granted a release permit, Binodoxys communis, was released in the summer of 2007 and 2008. At this time, it seems that Binodoxys has not establshed. However, there are three promising species for which permits are nearly ready. And much has been learned about the importation and release process.

One of these species is Aphelinus near engaeus, for which the petition to the North American Plant Protection Organization (NAPPO) for relapse has been approved. This species will be released and evaluated in the 2012-2014 field seasons. Other promising species that are being investigated under quarantine include Binodoxys koreanus and two populations of Aphelinus nr. gossypii. Approval for release of both of these species is expected for the 2013 field season.

Sources

Ecology and Management of the Soybean Aphid in North America. David W. Ragsdale, Douglas A. Landis, Jacques Brodeur, George E. Heimpel,and Nicolas Desneux. Annual Review of Entomology 56: 375-399.