Ovary development and egg load of soybean gall midge, Resseliella maxima (Diptera: Cecidomyiidae)

The soybean gall midge, Resseliella maxima Gagné, is a new pest of soybean in the Midwest U.S. Many aspects of R. maxima biology are poorly understood, including its reproductive biology. Most cecidomyiids are described as pro-ovigenic, meaning they emerge with a full complement of mature eggs, but this has not been confirmed for R. maxima. This study aims to characterize ovary development during the pupal and adult stages, and to assess egg loads of mature females. To characterize R. maxima ovary development, we dissected a series of individuals from the pupal stage to 48 hours post adult emergence. The ovaries dissected were stained with DAPI for fluorescence microscopy analysis of nuclear morphology and egg chamber development. In a second experiment, to assess egg loads of unmated females, we dissected females 48 hours post emergence. The number of eggs was counted using light microscopy, and wing and tibia lengths were measured to generate data for correlating egg number and female size. We found that ovary differentiation began approximately 24 hours after pupation. Unmated females at 30 minutes and 12 hours post-emergence contained only immature eggs. At 24 hours, both mature and immature eggs were observed, with fewer immature eggs in 48-hour-old females. The data for egg load of R. maxima is still being collected. The results from this study will improve our understanding of R. maxima egg development and provide insight into the reproductive potential of this pest.