Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2009
Publication Date: 7/27/2010
Citation: Spurgeon, D.W. 2010. Efficacy of Beauveria bassiana against Lygus hesperus (Hemiptera: Miridae) at Low Temperatures. J.Entomol. Sci. 45: 211-219. Interpretive Summary: The western tarnished plant bug is attacked by the naturally-occurring fungal disease, Beauveria bassiana, in the San Joaquin Valley of California. Recent efforts have focused on selecting Beauveria strains that are effective against plant bugs under the high-temperature conditions typical of the cotton production season. However, the most appropriate use of this fungus may be against wintertime populations of Lygus if strains are available that are effective under low temperature conditions. One commercially-available strain and four native strains of B. bassiana were tested against western tarnished plant bugs under temperatures of 55, 65, and 75°F. Although the fungus killed fewer bugs and the symptoms of disease occurred more slowly as temperatures were decreased, no differences in effectiveness were found among the tested strains. Although some strains of the fungus caused disease symptoms at different times than others, those differences were relatively small. Overall, the study did not show that any of the tested strains of B. bassiana were superior to the commercially-available strain under low temperature conditions.
Technical Abstract: The western tarnished plant bug, Lygus hesperus Knight, is attacked by the naturally-occurring pathogen, Beauveria bassiana (Balsamo) Vuillemin, in the San Joaquin Valley of California. Recent research efforts have focused on selection of Beauveria strains that were effective against Lygus under the high-temperature conditions typical of the cotton (Gossypium spp.) production season. However, the most appropriate use of this pathogen may not be as a rescue treatment. Alternatively, B. bassiana may be useful to efforts to target overwintering populations of Lygus if isolates are available that are highly virulent under the low temperature conditions typical of winter and early-spring in the San Joaquin Valley. One commercially-available isolate and four native isolates of B. bassiana were assayed against L. hesperus adults under constant temperatures of 12.8, 18.3, and 23.9°C. Although decreasing temperatures were associated with diminished Beauveria-induced mortality of Lygus and slower development of infection symptoms, no differences in efficacy were detected among the tested isolates. Differences in the patterns of occurrence of Beauveria infection symptoms were observed among isolates at some temperatures, but those differences were not substantial. Furthermore, results at some temperatures suggested potential influences of Lygus adult age or gender on susceptibility to B. bassiana. Those effects should be further investigated. Overall, the results did not indicate that any of the tested isolates of B. bassiana were superior to the commercially-available isolate under low temperature conditions.