Cross-resistance of Cry1Ac-resistant Heliocoverpa armigera Hübner

A population of cotton bollworm, H.armigera , selected for 26 generations with transgenic cotton producing Cry1Ac toxin developed 11.6-fold resistance to Cry1Ac, and another population was selected by Btk for 26 generations with 5.9-fold increase of LC50 s in laboratory. Cry1Ac resistant population with 5.4-fold to Cry1Ac caused 3.7-fold cross resistance to Cry1Ac+1C, no cross resistance to Btk, Bta, and Cry2A. Btk selected population with 4.1 fold to Btk caused 2.3- , 3.1- , 2.3-fold cross resistance to Bta, Cry1Ac, Cry1Ac+1C, respectively, and no cross resistance to Cry2A. There is no cross resistance to methomyl, phoxim, cypermethrin in these selected colonys. It suggested that conventional insecticides will be useful in Bt resistance management.