D3030: Developing a bioassay to evaluate soybean gall midge (Diptera: Cecidomyiidae) susceptibility to imidacloprid

Soybean gall midge, Resseliella maxima Gagné (Diptera: Cecidomyiidae) was first identified in 2019. Since then, there has been a search to find the effectiveness of different insecticide modes of action to mitigate the damage caused by this new soybean pest. Imidacloprid has been tested in field experiments over the past couple of years in eastern Nebraska to evaluate its effectiveness against soybean gall midge. However, results were varied between sites and years when the research was conducted. Therefore, a bioassay was developed to determine the lethal concentration of imidacloprid to better understand its effectiveness as a tool to control soybean gall midge. Soybean stems infested with soybean gall midge larvae were collected from two different counties in eastern Nebraska and brought to the laboratory for testing. Larvae were exposed to seven concentrations of imidacloprid and water control, and ten larvae were transferred per treatment. The concentration range was repeated at least three times per population. Mortality was assessed after 24 and 48 hours to estimate the LC50. Soybean gall midge larvae were considered dead if no movement was observed when touched with a fine-haired paintbrush. These results indicated that the method developed could be adopted to evaluate soybean gall midge susceptibility to imidacloprid and determine if imidacloprid seed treatment has a potential role in management for this new soybean pest.