Enhancing the efficacy of Beauveria bassiana for mole cricket (Orthoptera: Gryllotalpidae) control in turfgrass

by 1977- Thompson, Sarah Rachel

THOMPSON, SARAH RACHEL. Enhancing the Efficacy of Beauveria bassiana for Mole Cricket (Orthoptera: Gryllotalpidae) Control in Turfgrass. (Under the direction of Rick L. Brandenburg.) The objectives of this research conducted with the entomogenous fungus, Beauveria bassiana, include: a) to measure the effect of UV exposure and applied irrigation on the viability of conidia when applied to turfgrass b) to determine the type of interaction that exists between various strains of the fungus and other insecticides (imidacloprid and diatomaceous earth) and c) to elucidate the mechanism that mole crickets use to detect and avoid contact with the conidia. All three studies focused on two strains of B. bassiana, 5977 and 3622, that were originally isolated from orthopteran hosts and obtained from the ARS Collection of Fungal Cultures (Ithaca, NY). Other strains evaluated include strains DB-2 and MC, which were isolated from a darkling beetle and a tawny mole cricket, respectively. These four strains were propagated and formulated by JABB of the Carolinas, Inc. (Pine Level, NC). A commercially available strain, GHA formulated as BotaniGard® ES, from Emerald Bioagriculture Corporation (Butte, MT) was also evaluated. Field research to evaluate the impact of UV light and moisture on conidial viability was conducted on Bermudagrass Cynodon dactylon ( L.) plots at BASF Research Station (Fuquay-Varina,, NC) in July-August 2004 and August-September 2005. In a baseline viability study, there were no differences between strains 5977 and 3622 and both strains were able to persist in the environment up to 21 days after application. There were significant differences overall for both strains at two different levels of irrigation, with plots receiving 15.3 cm of irrigation during the study maintaining spore viability better than plots receiving 7.5 cm of irrigation. Different carrier formulations also significantly affected conidial viability for strain 3622. Oil formulations containing an optical brightener or magnesium silicate clay increased conidial viability by approximately 10% compared to the oil or clay alone formulations. Laboratory topical bioassays were conducted in June 2004 and 2005 on adult southern mole crickets to determine the interaction between B. bassiana and diatomaceous earth (DE) or imidacloprid. For all three strains tested, 5977, 3622, and GHA, there was significantly more mortality in combination treatments involving the fungus and DE compared to either treatment alone at a sublethal dose. These interactions were synergistic for strains 5977 and 3622. The percentage mortalities caused by combination treatments involving sublethal doses of imidacloprid and B. bassiana were less than additive for all three strains. This interaction was antagonistic for strain 5977. Combination treatments with diatomaceous earth caused as much mortality as high rate doses of the fungus alone for all three strains. Behavioral studies using tawny nymphs and southern adult mole crickets were conducted during the spring and fall of 2005 to determine the mechanism that mole crickets use to detect and avoid contact with B. bassiana conidia. A two-chamber test unit was designed utilizing infrared emitters and detectors to monitor mole cricket movement in areas adjacent to and containing fungal treated or untreated sand. Significant variations in behavior that suggest a chemosensory mechanism of detection were observed between treated and untreated chambers. Avoidance behaviors were more extreme for the southern mole crickets, suggesting a more sensitive response. Results from these studies emphasize the impact of abiotic factors on the use of B. bassiana as a biological control agent for mole crickets and suggest methods to increase efficacy of the fungus.