Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) Susceptibility to Bacillus thuringiensis Crystal Toxins

Authors: Muhammad Jawad Saleem, Faisal Hafeez, Muhammad Arshad, Afifa Naeem, Ayesha Iftekhar

Abstract:

Bacillus thuringiensis is a gram-positive spore-forming bacterium that belongs to the Bacillus cereus group of Bacilli and it produces ICP (insecticidal crystal protein) Cry toxins or Cysts toxins. Spores are produced as parasporal crystalline inclusions bodies (also known as endotoxins) at the onset of sporulation during the stationary growth phase. During vegetative growth that does not form crystals and is called vegetative insecticidal proteins (VIP) and secreted an insecticidal protein (SIP). Bacillus thuringiensis (Bt) is important for pest management either in the form of insecticides or through incorporated in the gene of the crop. Bioassays were conducted on the F2 generation of 1st instar larvae of H. armigera by the diet incorporation method to determine the susceptibility to Bt Cry toxins (Cry1Ac, Cry2Ab, Cry2A). The median lethal concentration (LC₅₀) of Cry1Ac, Cry2Ab, Cry2A ranged from 0.11 to 1.06 µg/ml and moult inhibitory concentration (MIC₅₀) of Cry1Ac, Cry2Ab, Cry2A ranged from 0.05 to 0.25 µg/ml. Cry1Ac was found most toxic to 1st instar larvae of H. armigera as compared to other Bt Cry toxins (Cry1Ac, Cry2Ab, Cry2A). The experimental results are important to policy-makers and technology providers to develop strategies for the exploitation of transgenic Bt cotton varieties as a component of integrated pest management.

Keywords: Bt toxin, Cry1Ac, Cry2Ab, Cry2A, susceptibility, Helicoverpa armigera