Which of the following microbes is not used as a biocontrol agent?

The correct answer is Option (1) → Lactobacillus

Option (1) Lactobacillus — Not used as a biocontrol agent. It is the lactic acid bacterium that turns milk into curd.

Option (2) Bacillus thuringiensis — Used as a biocontrol agent. Its spores kill butterfly caterpillars.

Option (3) Trichoderma — Used as a biocontrol agent. These fungi control several plant pathogens.

Option (4) Nucleopolyhedrovirus — Used as a biocontrol agent. Baculoviruses of this genus kill insects, species-specifically.

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).”
Microbes as Biocontrol Agents – “… Trichoderma species are free-living fungi that are very common in the root ecosystems. They are effective biocontrol agents of several plant pathogens.”