Cold tolerance of the invasive kudzu bug and its potential impact on soybean production in the Northeast
Megacopta cribraria, the kudzu bug, is an invasive pest of soybeans in the United States. The kudzu bug expanded to Maryland by 2013 since its introduction to Georgia in 2009 but has not continued to move northward. This project seeks to determine the physiological cold tolerance limits of the bug as well as the timing of movement to overwintering locations. The temperature at which an insect’s body freezes, known at the super cooling point, was measured across three populations over the fall of 2015. The average super cooling point across months and populations was 9.3±6.3°F. The lower lethal temperature to kill 50% of the population was measured concurrently with the super cooling point and was on average 22.8°F with a 95% confidence interval of 21.2°F to 24.1°F. A cage experiment and field sampling was used to determine the timing of movement to overwintering locations. Both the cage and field sampling indicate movement from the vines of kudzu plants to the leaf litter between late November and early December. The leaf litter provides a thermally buffered location for the bugs to overwinter. If an early cold front occurs, the kudzu bug would be in danger of high mortality. Producers can use the super cooling point, lower lethal temperature 50 temperature thresholds, and the timing of overwintering movement to predict the survival of the kudzu bug during the winter. A warmer than average winter would indicate a higher possible pest pressure in the spring in Maryland. The threshold may also be used to forecast range expansion in the future. The bug is currently restricted in range to the north by its cold tolerance yet may expand northward given warming winter temperatures.
Objective one states: measure key responses, such a thermal limits on survivability, to cold tolerance in association with overwintering across a range of kudzu bug populations. The super cooling point and lower lethal temperature to kill 50% of the population was assessed over three populations corresponding to different climatic zones in northern Virginia and southern Maryland. Each population was sampled in during the fall of 2015. Analysis of the key responses is complete.
Objective two states: observe kudzu bug phenology and movement to overwintering locations in the fall to determine temperature and realized overwintering population size. Timing of fall movement was assessed in a cage experiment and at three field locations in the fall of 2015. The cage experiment is currently being repeated for a second year.
Objective three states: create a model for integrated pest management and communication of findings with soybean producers and the agricultural community at large. Thresholds and predictions of future range expansion are established for modeling winter survival of the kudzu bug. The website mdkudzubug.org is updated when new information becomes available.
Work this year has been to analyze the data from the super cooling point, lower lethal temperature, and fall movement studies of the previous fall. At the end of this summer the cage experiment was set up for a second run and was monitored throughout the fall. In addition, two conference presentations were given on the cold tolerance work. Overall, the project has progressed at expected.
Impacts and Contributions/Outcomes
The impact of this project is to help producers assess the risk of the kudzu bug both annually and in the future. Winter mortality determines spring population size and ultimately if the population size warrants agricultural monitoring. The super cooling point and lower lethal temperature to kill 50% of the population can be applied to the winter temperatures measured in a given year. Whether or not these thresholds are surpassed allows producers to evaluate the pest pressure for that coming spring. When these thresholds are applied to average winter minimum temperatures, producers can assess risk based on range limitations and possible range expansion under warming winters. Cold tolerance findings were presented at the Eastern Branch of the Entomological Society of America annual meeting as well as the International Congress of Entomology conference.