Which of the following statements about Bacillus thuringiensis (Bt) are correct?

I. Bt bacteria are utilized as a means of controlling butterfly caterpillars.

II. A mixture of fresh Bt spores and water is sprayed onto susceptible plants like brassicas and fruit trees.

III. Insect larvae that consume Bt experience mortality due to the toxin released in their digestive system.

IV. Plants have been genetically modified to contain Bt toxin genes, providing them with resistance against pests.

I, II, III and IV

The correct answer is Option (4)-  I, II, III and IV

The correct statements about Bacillus thuringiensis (Bt) are as follows:

I. Bt bacteria are used to control butterfly caterpillars. These bacteria produce a toxin that is harmful to certain insect pests, including butterfly caterpillars.Bt toxin is produced by a bacterium called Bacillus thuringiensis (Bt for short). Bt toxin gene has been cloned from the bacteria and been expressed in plants to provide resistance to insects without the need for insecticides; in effect created a bio-pesticide. Examples are Bt cotton, Bt corn, rice, tomato, potato and soyabean etc.

II. To apply Bt as a biocontrol agent, fresh spores of the bacteria are mixed with water and sprayed onto susceptible plants such as brassicas (cabbage family) and fruit trees. This helps to target the specific pests that may be present on those plants.

III. B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. Actually, the Bt toxin protein exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of the insect.

IV. Bt toxin genes have been introduced into plants through genetic modification. This genetic modification provides the plants with resistance against pests, as the Bt toxin is produced within the plant tissues itself.

Overall, Bt is an effective biocontrol agent that can selectively target and control certain insect pests, offering an alternative to chemical pesticides.