D3424: 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 adult stage and assess egg loads of unmated females. To characterize R. maxima ovary development, we dissected a series of individuals at 0.5 hours, 12 hours, 24 hours and 48 hours post-emergence. The dissected ovaries were fixed and 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, dissections were performed at the same time points. The numbers of eggs were counted using fluorescence microscopy, and hind tibia lengths were measured to generate data for correlating egg number and female size. We found that unmated females contained only immature eggs at 0.5- and 12-hours post-emergence, while both mature and immature eggs were present at 24 and 48 hours. Egg load was positively correlated with female size, with a preliminary estimate of an average of 175.74 eggs per female. These results advance our understanding of R. maxima reproductive biology by demonstrating that females mature eggs after emergence and that egg load increases with body size.