Cold tolerance of the invasive kudzu bug and its potential impact on soybean production in the Northeast
Kudzu bugs, Megacopta cribraria, is a recent invasive pest of soybean in the Southeastern United States. The bugs are found as far north as Maryland but are not yet a significant agricultural pest at this northern limit. Cold tolerance seems to currently limit the range of the bugs. With mild winters and potential climate change, kudzu bugs may continue to expand their distribution northward. Knowing the cold temperature impacts on kudzu bugs could not only give insight to range expansion but also could factor into determining the spring population size and related outbreak potential. For measures of cold tolerance, we studied three populations at different climate zones in Maryland and northern Virginia. Sites were visited monthly in the fall and the super cooling point (SCP) was determined each month. The lethal temperature to kill 50% of the population (LT50) was determined twice during the fall. The SCP and LT50 did not vary greatly between sites or between months. For October and November, the SCP temperature ranged from -6.8 to -19.9 °C. We also assessed timing of movement to overwintering location at three field sites and one caged site. Observations revealed that the bugs remain in kudzu vines until the plants senesce. In total this work can be communicated to producers and used in an integrated pest management plan aimed at modeling kudzu bug expansion and outbreak potential.
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 responses chosen to measure were the super cooling point (SCP), and the lethal temperature to kill 50% of the population (LT50). Three sites were selected, each in a different climatic zone as determined by the USDA plant hardiness map. Insects were collected each month from October to December and SCP was determined. One site was omitted in December due to complete loss of the population to fungus. The LT50 was only determined for the first two months as population sizes were insufficient in December to perform the testing.
Objective two states: Observe kudzu bug phenology and movement to overwintering locations in the fall to determine temperature and realized overwintering population size. Movement was assessed through a field and caged study. The field component consisted of three sites in which five random samples were taken of vine, leaf litter, and soil once a month from October to December. Number of individuals of adults and nymphs found in the different categories were counted. The caged study was located on the campus of the University of Maryland. In the cage was an arrangement of plants and overwintering locations. The cage was monitored twice a week from October to December for movement of insects. Upcoming, the cage will be destructively sampled to determine overwintering location and apparent survivorship.
Objective three states: Create a model for integrated pest management and communication of findings with soybean producers and the agricultural community at large. Work on this objective relies upon finishing analysis of the first two objectives. Outreach to date is continued updating of information on our website (mdkudzubug.org) and an upcoming presentation at the Eastern Branch of the Entomological Society of America.
The grant was awarded this year and initial work involved purchasing equipment needed to perform the cold tolerance testing. September consisted of setting up the caged study, picking field locations and configuring the cold-water bath for running initial testing on the operation of the equipment. October through December consisted of collecting kudzu bugs from the field sites during the first two weeks of each month and then processing those samples for SCP, LT50, and movement data. Also occurring at this time, the field cage was stocked with bugs and then monitor twice a week. The project has been running as planned with the exception of losing one site in December to fungus issues. Continued work on the project this spring will be to analyze the data collected this fall, begin a predictive model, update our website, and continue to be available for talks with producers or the community at large.
Impacts and Contributions/Outcomes
Future impacts of this project will help producers in predicting if areas will be at risk in the future due to range expansion as well as assess the year to year outbreak potential within in the bugs current range. Most of this work relies upon creating a predictive model that combines the relationship of the bug to temperature with observed and future temperatures in an area. For example the SCP and LT50 may be applied with microhabitat adjustments to the measured ambient temperature to predict that year’s winter mortality. Knowing the mortality can then be used to determine the spring population size and if the population size is sufficiently large to need monitoring or not.