In Bt cotton, the Bt toxin present in plant tissue as pro-toxin is converted into active toxin due to the Action of gut microorganisms. Presence of conversion factors in insect gut. Alkaline pH of the insect gut. Acidic pH of the insect gut.

Bt-proteins require certain specific conditions for them to be active against the target insects. These include: a) The concerned Bt protein has to be ingested by the susceptible larvae as it has no contact effect. This is so because the native Bt protein is a 'protoxin' and has to be activated which occurs in the midgut of only the susceptible larvae. b) The insect gut should be alkaline (pH 9.5 and above for Lepidoptera) and also contain a proteolytic enzyme (Trypsin) for activating the Bt protein. c) There should be specific receptors in the midgut for the activated protein to bind and initiate structural and physiological changes leading to larval death.