Toxicity of Cotton Varieties Expressing Cry Proteins to Different Larval Instars of a Brazilian Helicoverpa armigera (Lepidoptera: Noctuidae)

Bioassays of H. armigera caterpillars at different larval stages fed plant structures of the Bt varieties were carried out to evaluate the effects of each variety on pest mortality, as well as possible sublethal effects on surviving individuals. The Bt varieties DP 555BGRR^® (Cry1Ac), FM 975WS^® (Cry1Ac + Cry1F), DP 1228B2RF^® (Cry1Ac + Cry2Ab2), and FM 940GLT^® (Cry1Ab + Cry2Ae) were effective in the control of H. armigera, reducing the survival of caterpillars; moreover, larval periods and pupal weights of surviving caterpillars fed the Bt varieties DP 555BGRR^® and FM 975WS^® were extended and reduced, respectively.