Evaluating several entomopathogenic fungi for control of soybean gall midge

Soybean gall midge, Resseliella maxima, is a cecidomyiid pest of soybean in the Midwest United States that was first described in 2019. As of 2023, it was found across six states. The larvae feed in soybean stems leading to lodging and death of plants, and can cause substantial yield loss, particularly along field edges. After three instars, larvae drop out of stems to pupate in the soil. Control of R. maxima is challenging due to it living much of its life protected in soybean stems or in soil. One form of biological control that has not yet been evaluated is entomopathogenic fungi (EPF). Many strains of fungi are pathogenic to insects, and fungal spores can be mixed into commercial formulations for field application. Some fungi can also establish in soil or endophytically within plants, potentially penetrating these sheltered habitats. To evaluate the baseline potential of EPFs for control of R. maxima, we directly exposed mature R. maxima larvae to spore formulations of five different EPFs. These included common commercially available EPFs, such as Beauveria bassiana, as well as several other promising species. After exposure, we transferred larvae to sand in plastic vials in order to pupate. A subset of vials was inspected for mycosis after 12 days, and the remaining vials were allowed to complete development to adulthood. Rates of successful infection (mycosis), mortality, and adult emergence will be compared between the different EPFs tested.