A second locus associated with high-level resistance to Bt Cry1Ac in Trichoplusia ni

The soil bacterium Bacillus thuringiensis (Bt) and its insecticidal Cry proteins are widely used for insect control in agriculture and public health. Continuing success of Bt biotechnology requires a better understanding of the insect genes involved in the toxicity of Bt proteins and their mutations leading to Bt resistance. Cry1Ac is a major Bt protein used for Lepidoptera pest control, and resistance to Cry1Ac has occurred in field populations of insects, including the cabbage looper, Trichoplusia ni. The results from this study confirmed that Cry1Ac resistance in an insect may involve multiple gene mutations and both dominant and recessive resistant traits. This study also revealed that the dominance of a resistance trait can be influenced by the genetic background of an insect population, which could complicate research data interpretation and may affect the efficacy of Bt toxins for control of different insect populations in the field.