Baseline toxicity of Bacillus thuringiensis insecticidal proteins Cry1Ac and Cry2Ab2 on the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) versus susceptibility to pyrethroids in Burkina Faso.

Résumé

Geographic variation in the sensitivity of cotton bollworm to B. thuringiensis insecticide proteins Cry1Ac and Cry2Ab2 was studied to establish a geographic baseline for comparing the future populations’ responses to the increased use of B. thuringiensis products in agriculture in Burkina Faso. The bollworm populations were collected from 3 ecological cotton areas in Burkina Faso and their susceptibility to Cry1Ac and Cry2Ab2 proteins were evaluated by diet contamination method; their susceptibility to deltamethrin was evaluated by topical application. The LC₅₀s (50% lethal concentration) resulting in larval mortality were ranged from 0.003 to 0.109 µgml^-1 of diet and from 0.341 to 4.222 µgml^-1 for Cry1Ac and Cry2Ab2 respectively, with resistance ratios ranged from 0.2 to 7 and 1 to 7 for Cry1Ac and Cry2Ab2 respectively. The same field strains had resistance ratios to deltamethrin ranged from 11 to 69. These data will be useful as baseline susceptibility index for resistance monitoring in H. armigera field strains in Burkina Faso.