Characterizing parasitism of 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 plant stems and can cause lodging, wilting, and plant death, reducing the field yield up to 31%. Management strategies for this pest are still being developed, and little is known about the potential for biological control. Here we examined parasitism of soybean gall midge through emergence cages and molecular biology. For this, two fields with R. maxima infestation were sampled in southwest Minnesota every 15 days. On each sample date, injured soybean plants were collected from edge and interior locations. For the molecular biology assays, one subset of stems was dissected, and R. maxima larvae were counted and preserved. The remaining subset of stems was 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. A species of Synopeas (Hymenoptera: Platygastridae) was found to be the dominant parasitoid. A Synopeas specific primer was developed, and real time qualitative PCR was performed on the preserved larvae to evaluate parasitism rates. Here we report the temporal and spatial dynamics of this parasitism in the field. Results of this study will inform the development integrated pest management programs for R. maxima.