The process follows a sequence from ingestion to the eventual death of the insect by Bacillus thuringiensis (Bt):
Ingestion: The insect must eat the Bt spores and crystalline protein toxins (Cry toxins) found on treated plant surfaces or expressed within genetically modified Bt crops.
Solubilization and Activation: Once inside the insect’s midgut, the alkaline environment (high pH) causes the toxin crystals to dissolve. Midgut enzymes then break down these crystals into smaller, activated toxin proteins.
Receptor Binding: The activated toxins bind to specific protein receptors (such as cadherin or alkaline phosphatase) located on the lining of the insect’s gut wall. This “lock and key” fit is why Bt is harmless to humans and other non-target animals, as they lack these specific receptors.
Pore Formation: Upon binding, the toxins insert themselves into the gut cell membranes, creating tiny holes or pores.
Gut Paralysis and Septicemia:
–Feeding Stop: These pores cause an osmotic imbalance, leading to gut paralysis. The insect stops eating within minutes or hours.
–Infection: The damaged gut wall allows the Bt spores and normal gut bacteria to leak into the insect’s body cavity (hemocoel), causing a widespread lethal infection known as septicemia.
Death: The insect shrivels, turns black, and typically dies from starvation or infection within 1 to 5 days.
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