Antagonistic effect of CrylAc and Cryljb on cotton bollworm(Helicoverpa armigera)

摘要

The insecticidal bacterium Bacillus thuringiensis has been widely used in agriculture for the control of insect pests in crops (Federici 2005). The main Bt toxic factor, cry 8-endotoxins, is produced as crystal parasporal bodies that form a large family of proteins with a remarkable structure similarity but with a wide target diversity. Cryl class comprises several cry toxins that are highly specific for the lepidopteran pests, which kill them following a unique mode of action. These proteins are based on solubilization and partial proteolysis in the insect intestine, in which the activated toxins interact with the member of columnar cells of the intestinal epithelium and damage the integrity of gut lining; this is followed by paralysis of the hostand death. Although the cryl type proteins share about 90% amino acid sequence identity, different insecticidal specificities have been reported for several lepidopteran insects (Milne et al. 1990). It has been suggested that mixture of functionally diverse toxins might be more effective than single toxins and might also delay evolution of resistance in target insects. Few workers have attempted to evaluate the combined action of toxins that naturally occur together or experimental mixtures of differenttoxins. Synergistic interactions between different 5-endotoxins have been described earlier. Other studies of interactions between 8-endotoxins have revealed additive effects and there has been only very few reports concerning unambiguous antagonism between closely related toxins. This is the first report where CrylAc and CrylJb toxins are showing antagonistic effect on cotton bollworm (Helicoverpa armigera).