Identifying Interactions and Dissemination Pathways of Beauveria bassiana among Kudzu, Kudzu Bug, Soybean, and the Soil

Kudzu bug, Megacopta cribraria, is native to Asia and is an invasive insect pest within the United States, where it was first discovered in 2009 in Georgia on urban structures and in Tennessee in 2012. Kudzu bugs feed on kudzu, Pueraria montana, and soybean, Glycine max, where they are an agricultural pest. One natural biological control of kudzu bug is the entomopathogenic and endophytic fungus, Beauveria bassiana. This fungus infects kudzu bugs and colonizes plant species, such as kudzu and soybean. In an assessment of the presence of B. bassiana in soil associated with kudzu, the number of colony forming units had similar proportions to both kudzu and kudzu bugs throughout a year. This finding indicates that these organisms interact with one another, especially when B. bassiana levels increase through the fall. However, the specific dissemination pathways of B. bassiana among these organisms and the soil are unknown. Therefore, studies were designed to isolate dissemination pathways among B. bassiana, soybean, kudzu bugs, and the soil. Inoculation methods that directly exposed soybean, kudzu bug, and the soil to B. bassiana spores resulted in higher colonization, indicating dissemination of the pathogen is mainly spread through direct contact of the spores among kudzu bugs, soybean, and the soil. However, colonization in all methods of inoculation decreased significantly over time. Kudzu bugs infected with B. bassiana that had spores on their outer surface were likely the leading contributor in the dissemination of spores to the soybean plant, soil, and other kudzu bugs. In an assessment comparing the effectiveness of a field-strain of B. bassiana to a commercial strain, both caused mortality of kudzu bugs over time with the commercial product causing 100% mortality by day one and the field-strain causing 90% mortality between days seven and nine. Findings indicate B. bassiana spores are more effective at colonizing soil, kudzu bugs, and soybean through direct contact. Identifying the specific dissemination pathways of B. bassiana among these organisms and the soil can be used to improve the use of B. bassiana in integrated pest management programs that target kudzu bugs in soybean.