Characterizing the community and impacts of parasitoid wasps attacking soybean gall midge in Minnesota

The soybean gall midge, Resseliella maxima (Diptera: Cecidomyiidae), is a new pest of soybean. The larvae attack the base of the stems, feeding on and damaging internal stem tissues. The feeding injury can cause lodging, wilting, and plant death, reducing the field yield up to 31%. Since 2019, when the insect was identified, it has been observed over an increasingly broad geography in the Midwest United States. Management strategies for this pest are still being developed, and little is known about its natural enemy community. We examined parasitism of soybean gall midge. For this purpose, 2 fields with R. maxima infestation were sampled in southwest Minnesota every 15 days. In each field, injured soybean plants were collected from edge and interior locations. The stems from each location were trimmed above and below the R. maxima lesions and kept in emergence cages in the laboratory. Cages were assessed daily for emergence of R. maxima adults and parasitoids. Here we provide the first documentation of parasitism of R. maxima, and report on the temporal and spatial dynamics of this parasitism in the field. A species of Synopeas (Hymenoptera: Platygastridae) was found to be the dominant parasitoid. Species-level identification of this wasp will require taxonomic study of the group, which has never been revised in North America. Results of this study will inform the development integrated pest management programs for R. maxima.