Promoting Sustainable Biological Control of the Soybean Aphid by Examining the Effect of Biodiversity on Releases of the Parasitoid Wasp Aphelinus glycinis

Promoting Sustainable Biological Control of the Soybean Aphid by Examining the Effect of Biodiversity on Releases of the Parasitoid Wasp Aphelinus glycinis

Summary

In an experiment conducted in 2015 at the U of MN Agricultural Experiment Station in Rosemount, MN, Aphelinus glycinis parasitoids were released in soybean fields adjacent to prairie plots and in control sites within the center of large monoculture soybean fields. The goal of the experiment was to evaluate whether the presence of prairie plantings would enhance parasitism in adjacent soybean plantings through supplementation of resources for the parasitoids. These resources could be floral or extrafloral nectar or alternative host (aphid) species present in the prairie plantings. Results showed that while the releases led to substantial levels of A. glycinis in both settings, parasitism was not higher adjacent to the prairie plots. Parasitism by a different parasitoid species, A. certus was also not enhanced by the prairie plantings. However, much higher levels of a third parasitoid species, A. asychis, were found adjacent to prairie than at control sites. This is the first discovery of this species at our field sites and the fact that it is found almost exclusively adjacent to prairie plots suggests that it is utilizing prairie-based resources. Since positive effects of the prairie on parasitism by neither A. glycinis nor A. certus were detected, we suspect that the resource provided by the prairie was an alternative aphid species that was used by A. asychis but not the other species.

We also evaluated overwintering of the parasitoid A. glycinis by monitoring A. glycinis mummies that had been released into a buckthorn stand at the U of MN Agricultural Experiment Station in St. Paul during the Fall of 2014. Buckthorn is the overwintering host of soybean aphid and this experiment was designed to determine whether A. glycinis can use soybean aphid to overwinter in buckthorn. Releases were done into sleeve cages and these cages were checked in April 2015 for evidence of successful overwintering. We found that a single A. glycinis individual successfully emerged from this experiment. While this is not strong evidence of overwintering, it suggests that this parasitoid species has the capability to overwinter in Minnesota.  This experiment is currently being repeated with a larger sample size.

Objectives/Performance Targets

During the summer of 2015 we conducted releases of A. glycinis adjacent to prairie vegetation and compared these releases to ones conducted at control sites that were within monoculture soybean fields. We also made progress on our objective of assessing the overwintering ability of A. glycinis by assessing the results of the 2014-2015 overwintering trials and initiating another round of such trials.

Accomplishments/Milestones

The parasitoid release study was successful in showing that A. glycinis was able to establish during the summer field season, but there was no significant difference in the level of establishment between the prairie and control plots by this parasitoid species. The study also showed that A. glycinis were found at only very low levels at sites 10m from the release, which suggests a low dispersal rate. Another soybean aphid parasitoid, A. certus was also not found in greater numbers near the prairie versus control sites, but a third species, A. asychis, was found attacking soybean aphid almost exclusively adjacent to the prairie plots (see figure).  Thus the presence of prairie vegetation appears to promote parasitism of soybean aphid by this parasitoid species. The 2014/2015 overwintering study resulted in successful overwintering of a single A. glycinis species.

Impacts and Contributions/Outcomes

Prairie plantings adjacent to soybean fields greatly enhanced soybean aphid parasitism by Aphelinus asychis in our study. A. asychis is native to Eurasia and was introduced into the Western U.S. to control the Russian wheat aphid in the late 1980s and has been sporadically reported attacking soybean aphid in the Midwest. The discovery that A. glycinis is able to overwinter in Minnesota is encouraging as well and we are following up on this discovery with additional studies.

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