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Question
Why do lepidopterans die when they feed on Bt cotton plant? Explain how does it happen.
Solution
Bacillus thuringiensis is a bacterium that produces proteins to kill certain insects such as lepidopterans (armyworm), coleopterans (beetles), and dipterans (flies/ mosquitoes). B. thuringiensis produces a protein crystal containing a toxic protein (inactivated state). This toxin is encoded by a gene called cry in the bacterium. Proteins encoded by genes cryIAc and cryIIAb control cotton bollworms and those encoded by cryIAb control corn borer.
When this inactivated toxin is ingested by the insect, it is converted into activated form due to alkaline pH of the gut. The alkaline pH of the gut results in the solubalisation of the crystal, thus converting it into the activated toxin.
Inactivated toxin`"alkline pH"/`> Activated toxin (gut of insect)
Activated toxin binds to the epithelial cells in the midgut of insect and creates pores that cause lyses and swelling and eventually death of insect.
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