Role of midgut digestive proteases upon sub-lethal exposure of Cry toxin in the larvae of castor semilooper, Achaea janata

Abstract

Development of synthetic insecticides to reduce the level of infestation led to deleterious effects on the environment and human health. This lead to the development of eco-friendly pest management alternatives including Bacillus thuringensis (Bt). Bt produces Crystal (Cry), Cytotoxic (Cyt) and Vegetative (Vip) proteins with insecticidal activity against different orders of Lepidoptera. Of late, pest resistance against Bt is being reported in many parts of the country. The foliar spray may lead to the reduced toxicity of Bt formulation from degradation by UV light, wash-off by rain, drying, temperature, and soil acidity as well as its chemistry. Further, insects sense pesticides through odorant receptors and move away quickly. Under these conditions, there is always a possibility of a population of larvae to get exposed to sub-lethal doses of toxin which might exhibit variable effects and escape mortality and eventually generate resistance. The role played by digestive proteases in the activation of the Cry toxin and digestion when administered in sub-lethal concentration could help in the elucidation of key phenomena like adaptations for survival and resistance development. Elucidation of these digestive proteases would enhance our understanding of resistance development. The current study is an attempt to monitor the transcript levels of digestive proteases upon sub-lethal exposure of Cry toxin in the larvae of an economically important polyphagous pest castor semilooper, Achaea janata prevalent in the Indian subcontinent.