This project in the second of three years specifically addresses a priority item listed under the category of Soybean Pest Management in the FY2023 request for proposals: ”Soybean farmers need continued research into cultural, chemical and biological control mechanisms for management of soybean insects including, but not limited to, soybean aphid,
Japanese beetle and soybean gall midge.” The methods proposed here were developed and successfully validated in the first year of the project.
Soybean gall midge, Resseliella maxima, is a new devastating pest of soybean in the Midwest (Gagné et al. 2019). Soybean gall midge larvae feed inside the stems of soybean plants near the soil surface (McMechan et al. 2021). Infestations cause wilting, lodging and death of soybean plants, and have resulted in significant yield reductions (McMechan et al. 2021). Currently, this pest is known to occur in Minnesota, Nebraska, Iowa, South Dakota, and Missouri (McMechan et al. 2021). In Minnesota, this pest has already been detected in at least 29 counties in the south and west (soybeangallmidge.org) and it may continue to spread to other areas.
Cold winter temperatures are an important factor, among several, limiting the geographic range and population sizes of insects in temperate regions like Minnesota (Bale 1996). Infestations by soybean gall midge have been more severe in Nebraska than in Minnesota, and the insect has not been detected in northern Minnesota. It remains unknown what role cold winter temperatures play in limiting populations of this pest. Understanding how a new pest like soybean gall midge responds to cold temperatures is foundational information for understanding its pest potential and for developing pest management programs. The ability of organisms to survive exposure to cold temperatures
is referred to as their cold hardiness. Because the soybean gall midge is such a new pest, there is no knowledge about its cold hardiness, and therefore we are limited in our abilities to predict how widespread it may become in Minnesota and to predict spring populations based on winter temperatures. These types of information have proven important for the management of other crop pests (e.g., corn earworm, bean leaf beetle, etc.).
Like related species of gall midges (e.g., the raspberry gall midge (Nilsson 2008)), soybean gall midge larvae drop from the soybean plants in the fall and enter the soil where they construct cocoons. The larvae spend the winter in these cocoons, often in the upper two inches of the soil surface. In spring, as soil temperatures rise, the larvae develop into pupae and then adults, which emerge to restart the life cycle. During the winter months, the larvae must survive extended periods of low temperatures (often around freezing) and occasionally extremely low temperatures.
The cold hardiness of insects is often evaluated by quantification of their supercooling points and lower- lethal temperatures (Sinclair et al. 2015). The supercooling point of an insect is the temperature at which the liquids in its body begin to freeze. Because of freeze-protective chemicals in insect bodies, the temperature at which insects freeze is often below the freezing point of water, hence the term “super”cooling. The lower-lethal temperature is the temperature at which the insect actually dies from cold exposure. By characterizing both the supercooling point and lower-lethal temperature of an insect, an understanding of the insect’s strategies for cold hardiness can be gained.
By acquiring an understanding of the cold hardiness of soybean gall midge, actionable models will be developed to predict the potential geographic range of the pest and levels of survival of the pest from one year to the next. Furthermore, this information will guide development of recommendations for cultural tactics (e.g., tillage, residue management, etc.) that could increase winter mortality of soybean gall midge and result in decreased pest populations.
We are proposing this as the second year of a three-year project to characterize the cold hardiness of soybean gall midge and develop actionable models and recommendations for its management. We are currently making great progress on the first year of the project. We have developed and successfully utilized the necessary methodology obtain initial estimates of cold hardiness (supercooling point and lower-lethal temperature) for soybean gall midge. However, as with other field research projects, we need to replicate this work in additional environments (years) to understand the natural variability in our system.
Our team at the University of Minnesota has extensive experience evaluating the cold hardiness of numerous insect pests and using that information to develop recommendations for farmers and land managers. We will collaborate with Dr. Robert Venette (USDA Forest Service/University of Minnesota) who has state-of-the-art equipment for assessing cold hardiness and considerable technical expertise in this area. This area of research is not being addressed by any of the Midwest researchers working on soybean gall midge; therefore, this project does not duplicate any existing efforts. Furthermore, this proposal has not been submitted to this or any other funding entity.