Which of the following statements about Bacillus thuringiensis (Bt) are correct?
I. Bt bacteria are used as a means of controlling butterfly caterpillars.
II. Dried Bt spores are mixed with water and sprayed onto vulnerable plants such as 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.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → I, II, III and IV
Bacillus thuringiensis (Bt) is a bacterium used for biological control of insect pests. All four statements match the book.
I. Bt bacteria are used as a means of controlling butterfly caterpillars. — True. Bt is the book’s example of a microbial biocontrol agent against butterfly caterpillars.
II. Dried Bt spores are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees. — True. Bt is sold in sachets as dried spores. These are mixed with water and sprayed on the plants.
III. Insect larvae that consume Bt experience mortality due to the toxin released in their digestive system. — True. The larvae eat the spores. The toxin is released in their gut and kills them, while other insects are left unharmed.
IV. Plants have been genetically modified to contain Bt toxin genes, providing them with resistance against pests. — True. By genetic engineering, Bt toxin genes have been put into plants such as Bt-cotton, which resist insect pests.
NCERT Extract:
Microbes as Biocontrol Agents – “… An example of microbial biocontrol agents that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt). 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. Because of the development of methods of genetic engineering in the last decade or so, the scientists have introduced B. thuringiensis toxin genes into plants. Such plants are resistant to attack by insect pests.”