Efficacy of Beauveria bassiana for control of Tribolium castaneum with reduced oxygen and increased carbon dioxide

Atmosphere modification by reducing oxygen or increasing carbon dioxide has been used widely in recent years as a chemical-free strategy for managing stored-product pest insects (Donahaye et al. 1996; Adler et al. 2000; Jayas and Jeyamkondan 2002). The red flour beetle, Tribolium castaneum (Herbst), being among the most problematic of stored-product insects, has been the subject of considerable research on the approach (Press and Harein 1967a; Storey 1977). This can be done by introducing gases or by hermetically sealing storage units. An approach proposed by Conyers and Bell (2007) is to employ moderate O2 reduction and CO2 elevation by continuous input of gases as might be accomplished with a gas burner. The authors expect this to cause life cycle disruption rather than complete mortality. Regardless of the approach, treatment areas with leaks, penetration problems or insufficient treatment times inevitably harbour many insects that are stressed but escape death. Resistance may also contribute to pest survival. In the laboratory, resistance development to reduced O2 (Donahaye 1990a) and enriched CO2 (Donahaye 1990b) has been reported. A T. castaneum strain that was selected for hypercarbia resistance was able to maintain water balance and energy reserves better than an unselected strain, while strains that were selected for either hypercarbia and hypoxia resistance had reduced metabolic rates (Donahaye 1992). A secondary, chemical-free control measure would be useful to address escapes and as a resistance management tactic. The entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin, has proven efficacy for many insect pests of stored grain and grain products but is not considered a commercially viable stand-alone option for controlling T. castaneum (Akbar et al. 2004; Lord 2007a). We have been investigating combination strategies as a means to improve B. bassiana’s performance against T. castaneum. Combination with diatomaceous earth was synergistic in laboratory assays (Akbar et al. 2004), and desiccation stress enhanced the fungus’ efficacy (Lord 2007b). Other than toxic stress from insecticidal compounds, the effects of host stress on the performance of entomopathogenic fungi has received scant attention. Temperature and nutritional stresses