By Jonathan Dregni
Cooperators are needed for a U of MN survey of soybean field for a parasitic wasp of soybean aphid. These wasps (called Aphelinus certus), which do not sting people, are working to prevent soybean aphid outbreaks. First detected in 2005, this parasitic wasp spread quickly across the North American range of soybean aphid, arriving in Minnesota in 2011. Larvae of the wasp live inside and eventually kill the aphids leaving dark-colored “mummies”, which look like inflated black aphids attached to soybean leaves and stems. Adult wasps emerge from the mummies, mate, and immediately begin laying eggs in nearby aphids. Many generations of this wasp occur over the course of the summer.
With the assistance of the Minnesota Department of Agriculture we conducted statewide surveys of soybean aphid and Aphelinus certus. Scouts visited soybean fields in 43 Minnesota counties and sent thousands of mummy-infested soybean leaves to our St. Paul laboratory, where we reared them to determine species, sex ratio, and other important life history traits.
Our 2017 survey showed the highest aphid densities in the central and northwestern portions of Minnesota in late August (see Map 1, which show highest reported densities for each county). Aphelinus certus was also found throughout this region (see Map 2).
In 2018, the survey will continue but we need your help to find fields we can inspect for aphids and parasitic wasps. If you grow soybean, or work with someone who does, please email Jonathan ( firstname.lastname@example.org ) and include the location of the fields. We hope to visit soybean fields across the state between July 15 and August 15, 2018, and would love to include your part of the state. Contact us, and thanks for your support!
Pro tip: When managing soybean aphid, scout your fields and delay spraying until you reach the economic threshold (250 aphids per plant) to reduce insecticide inputs and conserve these aphid-killing wasps.
For true insect lovers: We also found 4 species of hyperparasitoids, which are parasitic wasps that attack the larvae of other parasitic wasps. For example, these wasps will lay their eggs into the larvae of Aphelinus certus that are already inside the soybean aphids.
Special thanks to the MDA (Jean Ciborowski, Angie Ambourne, and scouts Lisa Becker, Kim Sigurdson, Grace Sward, and Jerald Yourcek) and the UMN Biological Control Lab (Henry Davis, Jacqueline Nuzzo, and Elsa Ubel). This work is partially supported by the Minnesota Soybean Research & Promotion Council.
Map 1: Survey results for soybean aphid populations in Minnesota in 2017 (counties shaded in brown were not sampled).
Map 2: Survey results for the parasitic wasp (Aphelinus certus) populations in Minnesota in 2017 (counties shaded in brown were not sampled).