bacteria Bacillus thuringiensis (often written as Bt ). to control butterfly caterpillars
These are available in sachets as dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees, where these are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars, but leave other insects unharmed.
The Bt toxin is an inactive protoxin, which is activated due to the alkaline pH in the insect gut. Bt toxin dissolve in high pH of insect gut and become active. The toxins then attack the gut cells of the insect, punching holes in the lining.
(i) Insect eats Bt crystals and spores.
(ii) The toxin binds to specific receptors in the gut and the insects stops eating.
(iii) The crystals cause the gut wall to break down allowing spores and normal gut bacteria to enter the body.
(iv) The insect dies as spores and gut bacteria proliferate in the body.