Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/12/2007
Publication Date: 7/31/2007
Citation: Lord, J.C. 2007. Enhanced efficacy of Beauveria bassiana for the red flour beetle, Tribolium castaneum, with reduced moisture. Journal of Economic Entomology 100: 1071-1074. Interpretive Summary: Insecticidal fungi are environmentally benign alternatives to chemical methods of insect control, but appropriateness for the dry conditions of stored products is unproven. The red flour beetle is a pest of grain in storage and processing that is difficult to control with any available technology. Beauveria bassiana, a fungus that is registered for insect control on crops, was tested against the red flour beetle under various moisture conditions. The fungus’ efficacy for larvae was greatest under dry conditions that caused desiccation stress. The stress was confirmed by low weight gain and by exposure to desiccation prior to exposure to the fungus. Dry moisture conditions also favored the fungus’ performance for adult beetles. These results demonstrate that dry stored-grain conditions are favorable for B. bassiana efficacy against red flour beetle and will provide a basis for exploring the pest’s physiological vulnerabilities with molecular methods.
Technical Abstract: Tribolium castaneum is a problematic pest of stored and processed grains that is tolerant of Beauveria bassiana under most conditions. Laboratory assays demonstrated that desiccating conditions improved the fungus’s efficacy. For T. castaneum larvae exposed to B. bassiana at different vapor pressure deficits (VPD), the LC50 potency ratios were 2.3 for 2.42 kPa and 3.9 for 3.31 kPa as compared with 1.06 kPa. There were significant effects of moisture on B. bassiana-associated mortality even with brief exposure to low VPD before or at the beginning of fungus exposure. When T. castaneum larvae were held 3.31 kPa one day prior to exposure to B. bassiana and/or in the first one or two days of exposure to the fungus, there was significantly greater mortality for all of the low moisture treatments than occurred with continuous incubation at 1.06 kPa. Beauveria bassiana efficacy for adult T. castaneum was significantly better for VPDs of 3.56 or 3.78 than 1.06 kPa. Weight gain over four days of incubation with moisture held constant was significantly less at a VDP of 3.31 kPa then at 1.87 or 1.06 kPa. Fungus treatment did not affect weight gain significantly. There was no significant difference in larval water content among treatments.