D3282: Lower lethal temperature and time of soybean gall midge

Soybean gall midge, Resseliella maxima, is a recently established cecidomyiid pest of soybean in the Midwest United States. The first widespread outbreak was in 2018 and R. maxima was described in 2019. It has been found in new counties every year since and is now known in six states. Larvae feed internally in soybean stems and can cause substantial yield loss, concentrated along field edges. Upon maturity, larvae drop out of stems and pupate in the soil. Late-season larvae will overwinter within cocoons in the soil and pupate the following spring. Beyond this overwintering strategy, little is known about their cold tolerance or overwintering survival. Cold tolerance is an important factor driving population dynamics and range expansion, especially in the Midwest climate. To better understand R. maxima cold tolerance, we collected infested soybean stems from fields near southwest Minnesota in early September in 2022 and 2023. In the laboratory, we retrieved third-instar larvae from these stems and maintained the larvae at conditions to induce development of the overwintering stage (cocooned third-instars). These cocoons were then transferred to two different cold conditions (13°C or 3°C) with a short day length (10L:14D) to explore potential acclimation. After one and two months in these conditions, we measured lower lethal temperatures. In 2023, we also measured lethal time by holding cocoons at 3°C, -3°C, and -10°C for longer periods of time to test long-term survival. This poster will highlight the results of these experiments, and provide insight into the cold tolerance of R. maxima.