Production and characterization of Bacillus thuringiensis Cry1Ac-resistant cotton bollworm Helicoverpa zea (Boddie).

ABSTRACT Laboratory-selected Bacillus thuringiensis -resistant colonies are important tools for elucidating B. thuringiensis resistance mechanisms. However, cotton bollworm, Helicoverpa zea , a target pest of transgenic corn and cotton expressing B. thuringiensis Cry1Ac (Bt corn and cotton), has proven difficult to select for stable resistance. Two populations of H. zea (AR and MR), resistant to the B. thuringiensis protein found in all commercial Bt cotton varieties (Cry1Ac), were established by selection with Cry1Ac activated toxin (AR) or MVP II (MR). Cry1Ac toxin reflects the form ingested by H. zea when feeding on Bt cotton, whereas MVP II is a Cry1Ac formulation used for resistance se…