Comparative toxicity of Cry1Ac and Cry2Aa δ-endotoxins of Bacillus thuringiensis against Helicoverpa armigera (H.)

Abstract

Toxicity and larval growth inhibition of Bacillus thuringiensis proteins, Cry2Aa and Cry1Ac were evaluated against the neonate larvae of Helicoverpa armigera (Hübner) by a whole-diet contamination method. The median lethal concentrations (LC 50) of Cry2Aa and Cry1Ac were 1.57 and 0.24 μg/ml, respectively. Though Cry2Aa is less effective than Cry1Ac in killing H. armigera larvae, growth inhibition of the surviving larvae was severe and comparable in both Cry1Ac (99.3%) and Cry2Aa (89.9%) at a concentration of 0.5 μg/ml. Moreover, the mortality of H. armigera was more rapid with Cry2Aa than Cry1Ac. Hence, the Cry2Aa is suggested as an alternative for CrylAc in combating H. armigera that has the capacity to develop resistance against Cry1Ac.