Activity of the M-ONE Formulation of a New Strain of Bacillus thuringiensis Against the Colorado Potato Beetle (Coleoptera: Chrysomelidae): Relationship Between Susceptibility and Insect Life Stage

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Abstract
In laboratory experiments, 0.03-0.13 times the recommended field rate of a commercial formulation of Bacillus thuringiensis var. san diego (M-ONE) resulted in 40-98% mortality of second-instar Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), 96 h after they began feeding on treated potato foliage. An average of 52% mortality of third instars was recorded at 96 h. Separate feeding consumption studies demonstrated that surviving second instars were inhibited from feeding for at least 48 h after an initial 24-h exposure to potato foliage treated with B. thuringiensis var. san diego . Ingestion of B. Thuringiensis var. san diego inhibited feeding of third instars and adults, but they were able to resume feeding to a greater extent than second instars after the initial 24-h exposure period. Field applications applied to potatoes at 0.5, 0.75, and 1.0 times the recommended field rate resulted in significantly lower numbers of small and large larvae in treatment plots compared with controls. Potato tuber yields were significantly higher in plots treated with B. thuringiensis var. san diego than yields produced in control plots.