Figure 1.

Experimental design for crosses and bioassay to map Bt resistance. Single-pair crosses between LAB-PS and NO-QA virgin adults produced families of hybrid F₁ offspring. A female F₁ from hybrid family QS1 was backcrossed to a male NO-QA to produce a family BC1 of offspring; one of her F₁ brothers was backcrossed to a female NO-QA to produce family BC2. Approximately 80 backcross offspring from BC1 and BC2 were tested at 0.1 mg/ml Cry1Ac. Survivors were reared to adulthood and frozen for DNA analysis. About 30 additional backcross offspring from each family were reared to adulthood without exposure to Bt and frozen for DNA analysis.