Biological control and behavioral studies of mole crickets (orthoptera: Gryllotalpidae) with the entomopathogenic fungus, Beauveria bassiana (balsamo) vuillemin

by 1977- Thompson, Sarah Rachel

THOMPSON, SARAH RACHEL. Biological control and behavioral studies of mole crickets (Orthoptera: Gryllotalpidae) with the entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin. (Under the direction of Rick L. Brandenburg.) The objectives of this research conducted with the entomogenous fungus, Beauveria bassiana, include: a) to determine if a behavioral response occurs when mole crickets are exposed to conidia b) to measure the viability of conidia when applied to turfgrass and c) to evaluate the efficacy of various strains and rates of the fungus against mole crickets in a laboratory topical bioassay. All three studies focused on two strains of B. bassiana propagated and formulated by JABB of the Carolinas, Inc. (Pine Level, NC), DB-2 and 10- 22. A commercially available strain, GHA formulated as BotaniGard ES, from Emerald Bioagriculture Corporation (Butte, MT) was also evaluated. Greenhouse studies at North Carolina State University (Raleigh, NC) to determine behavioral changes in response to the fungus were conducted during the fall and winter of 2001-2002 and the spring and summer of 2003 using tawny and southern adult mole crickets. Significant variations in behavior were observed in containers treated with strain DB-2 and bifenthrin, indicating avoidance responses associated with these control agents. Field research to evaluate conidial viability was conducted on Bermudagrass Cynodon dactylon ( L.) plots at Sea Trails Golf Course (Sunset Beach, NC) in August 2002 and Tri- State Sod Farm (Newton Grove, NC) in June 2003. Strains DB-2 and 10-22 were significantly more viable than BotaniGard in the 2003 study but all three strains were able to persist in the environment up to 28 days after application in both field studies. 10-22 showed the best performance in both field tests as well as after day 7 in an accompanying greenhouse trial. The laboratory topical bioassay was conducted in August 2003 on tawny and southern mole cricket nymphs to determine the most efficacious strain and rate of B. bassiana. There were significant differences in survival functions for all fourteen treatments (four rates of each of the three B. bassiana strains as well as two control treatments). BotaniGard caused the greatest mortality in the shortest amount of time after exposure. The highest rate tested, 108 conidia per cricket, appeared to have the most considerable effect for all three strains as measured by total percent mortality and LT25. Results from these studies emphasize the importance of strain selection for the use of B. bassiana as a biological control agent for mole crickets. An appropriate isolate that maintains viability, effectively targets the host, and dose not elicit behavioral responses from the crickets will have the most potential as an efficacious control agent for these serious turfgrass pests.