Q.What is meant by "biological control" of pests and pathogens? Give one example each of a bacterium, a fungus and a virus used for this purpose.

Bacillus thuringiensis produces crystal (Cry) toxin proteins that specifically kill insect pests, and is used as a biopesticide / as the source of the Bt toxin gene in Bt crops.

Bacillus thuringiensis is a soil bacterium that, during sporulation, forms proteinaceous crystals containing an insecticidal protein called Bt toxin (Cry protein). When ingested by susceptible insect larvae (e.g. lepidopteran pests of cotton), the toxin binds to the gut wall, is activated, and causes gut cell lysis, killing the larva. It is used both as a natural spray-on biopesticide and as the gene source (cry genes) inserted into crops like Bt cotton to make them pest-resistant. It does not act against bacterial or fungal pathogens or nematodes.

Bacillus thuringiensis produces a crystal protein toxic to insect larvae, and is used as a natural, biological pesticide.

Bacillus thuringiensis (Bt) is a soil bacterium that produces a crystal (Cry) protein toxin that is lethal to the larvae of specific insect pests (e.g., lepidopteran pests) when ingested, but harmless to non-target organisms and humans. Preparations of Bt spores/toxin are used as an eco-friendly microbial insecticide sprayed on crops, and the Bt toxin gene has also been genetically engineered into crop plants (e.g., Bt cotton) to confer built-in insect resistance.

Among the options, Bacillus thuringiensis is the bacterial biopesticide — the answer is (d).

A bacterial insecticide is a bacterium used to control insect pests.

• (a) Verticillium sp., (b) Arthrobotrys sp., (c) Dactylella sp. — these are fungi (fungal biocontrol agents / nematode-trapping fungi), not bacteria.

• (d) Bacillus thuringiensis (Bt) — a bacterium whose spores contain crystalline Bt (Cry) toxin proteins; when eaten by insect larvae (e.g. of butterflies/moths) the toxin dissolves in the alkaline gut, ruptures the gut cells and kills the larva. Bt is widely sprayed as a biopesticide and its cry genes are engineered into Bt cotton/Bt corn.

A mycoherbicide is a fungal pathogen (or a formulated product derived from it) used as a biological agent to control weeds, e.g.

Mycoherbicides are fungi used to biologically suppress unwanted weeds.

A mycoherbicide is a biological weed-control agent made from a fungal pathogen that specifically infects and kills a particular weed species without harming the crop plant. It is an eco-friendly alternative to chemical herbicides because it targets only the intended weed, does not leave toxic residues, and self-perpetuates in the field once established. A classic example is Phytophthora palmivora, which is used as a mycoherbicide to control the weed milkweed vine (Morrenia odorata) in citrus plantations.