Selection of a Colorado Potato Beetle (Coleoptera: Chrysomelidae) Strain Resistant to Bacillus thuringiensis

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Abstract
For the first time, resistance to the CRYIIIA coleopteran specific delta endotoxin of Bacillus thuringiensis var. san diego or tenebrionis is reported. Colorado potato beetles, Leptinotarsa decemlineata (Say), were selected in the laboratory after exposure in potato fields in Michigan. After 12 generations of selection, the selected strain was 59 times more resistant than the unselected strain and 24-35 times more resistant than other susceptible or insecticide-resistant strains. We observed no cross-resistance between organophosphate, carbamate, or pyrethroid resistance and B. thuringiensis resistance. No difference in movement induced by B. thuringiensis or initial feeding behavior was observed between selected and unselected strains, although a shift toward petiole feeding behavior was observed in adults (of both strains) that were stressed by B. thuringiensis . The selected strain oviposited at a reduced rate of 0.1 ±0.15 (mean ± SD) egg masses per day) on treated foliage; the unselected strain was oostatic. Based on these results, it is recommended that resistance management strategies be developed and deployed for both conventionally applied B. thuringiensis products and B. thuringiensis transgenic plants.

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