Question

A microbial biocontrol agent that can be used to control butterfly caterpillars is:
A. Trichoderma polysporum
B. Bacillus thuringiensis
C. Streptococcus
D. Mycorrhiza

Answer 1

Microbial biocontrol of pests is a method of controlling pests, insects, disease, or weeds using microbial organisms. These microbes either cause disease to the pest, kill them, or compete with them. It is a soil-dwelling bacterium that secretes a toxin called the Bt toxin which when ingested by the larvae of insects such as butterflies dies and acts as a biocontrol agent.

Complete answer: Biological control or biocontrol is a method of controlling pests such as insects, mites, weeds and plant diseases using other organisms. There are three main strategies which include importation, augmentation and conservation. Importation refers to when a natural enemy of the pest is introduced, augmentation is when a large population of pest enemies is introduced for immediate control and conservation refers to where there is a reestablishment of natural enemies. Dragonflies and ladybugs are common insects that are used to eradicate pests such as aphids as they act as their natural enemies. Microbial pest control is one form of biological control, wherein microbes such as bacteria, fungi, protozoa, viruses, etc. are the primary source of controlling pests. Bacillus thuringiensis is a gram-positive soil-dwelling bacterium that has found its use as a biological pesticide. This bacterium produces a particular toxin named Bt toxin which remains inactive and only gets activated in the guts of the larvae of certain pests. As the larvae of pests such as butterflies or bollworms eat the leaves sprayed with the toxin, the toxin kills the species. The most notable feature is that this only affects certain species of pest and maintains the population of a native organism near the crops. This toxin is also safe to consume by humans and thus is widely regarded as a safe and effective biopesticide.
Therefore, the correct answer is option B.

Note: These bacteria naturally produce crystal toxins, which can be artificially synthesized. The synthesized crystals are dissolved in water and sprayed over crops. The specificity of the action is primarily because butterflies and other Lepidoptera species have an alkaline gut and possess the proteases to dissolve the crystal and release the toxin. These toxins disable their digestive tract which leads to starvation and death.