Microbes as Biocontrol Agents (NCERT) - Free MCQ Practice Test with solutions,

Bioinsecticides are those biological agents that are used to control harmful insects. Because of development of methods of genetic enginerring, B-Thuringiensis toxic genes are introduced into plants. Such plants are resistant to attack by insect pests. Bt cotton is one such example.

Xanthomonas campestris is not used as a biopesticide. Bacillus thuringiensis is used as a microbial biocontrol agent. Trichoderma harzianum is a free-living fungi, common in soil and root ecosystems. It is an effective biocontrol agent of several plant pathogens. viruses of the family Baculoviruses are pathogens that attack insecs and other arthropods. The majority of baculoviruses used as biological control agents belong to genus Nucleopolyhedrovirus.

Baculoviruses are pathogens that attack insects and other arthropods. The majority of them used as a biological control agents are in the genus Nucleopolyhedrovirus.These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications. Infection with baculoviruses occurs when susceptible hosts eat virus particle present on foliage and dies. These are important in organic farming because of their specific action on harmful insects without causing any damage to beneficial insects as well as to the environment.

An example of microbial biocontrol agent is bacteria Bacillus thuringiensis (Bt).
It can be introduced in order to control butterfly caterpillars.
These are available in sachets as dried spores that are mixed with water and sprayed onto vulnerable plants such as Brassica and fruit trees, where these are eaten by the insect larvae. In the gut of larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars, but leaves other insect uharmed. 

Nucleopolyhedrovirus are excellent candidates for species-specific, narrow spectrum insecticidal applications. They have been shown to have no negative impacts on plants, mammals, birds, fish or even on non-target insects. This is especially desirable when beneficial insects are being conserved to aid in an overall integrated pest management (IPM) programme, or when an ecologically sensitive area is being treated.

• Tricoderma is a biocontrol agent.
• Streptomyces is the source of antibiotic streptomycin.
• Azospirillum is a free-living nitrogen fixing bacteria.
• Lactobacillus produces lactic acid.

Ladybird and dragonflies are used to get rid of aphids and mosquitoes respectively. Bacillus thuringiensis bacteria are used to control utterfly caterpillars. Trichoderma species are used to control several plant pathogen.. 

Statement A is incorrect (biocontrol maintains balance, not eradication).
Statement B is correct (Bt genes used in transgenic plants).
Statement C is correct (baculoviruses are species-specific).
Statement D is incorrect (organic farming avoids chemicals).