Mortality of Colorado Potato Beetle (Leptinotarsa decemlineata) after Sublethal Stress with the CryIIIA δ-Endotoxin of Bacillus thuringiensis and Subsequent Exposure to Beauveria bassiana

Acute or chronic sublethal exposure of Colorado potato beetle larvae to the CryIIIA δ-endotoxin of Bacillus thuringiensis Berliner did not significantly (P > 0.05) alter their subsequent susceptibility to Beauveria bassiana (Balsamo) Vuillemin. During the period of exposure to B. bassiana there was continued mortality from previous exposure to δ-endotoxin, and B. bassiana also caused significant mortality. Acute and chronic exposure to δ-endotoxin significantly prolonged larval development. The weights of prepupae and adults were significantly reduced by exposure to δ-endotoxin, with the greatest effect being from chronic exposure. Separation of the manifestations of stress in time (feeding vs soil stages) and space (toxin damage to the insect gut vs fungal penetration of the cuticle and activity in the hemocoel) may have precluded alteration of insect susceptibility to infection by B. bassiana. Endemic populations of B. bassiana are not expected to influence the development of resistance in the Colorado potato beetle to the δ-endotoxin of B. thuringiensis.