A second locus associated with high-level resistance to Bt Cry1Ac in <i>Trichoplusia ni</i>

strains. The results from this study demonstrated that resistance to Cry1Ac in an insect may involve multiple gene mutations with various types of dominance, and the dominance can be influenced by the genetic background of an insect population. IMPORTANCE: . 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.