What makes baculoviruses species-specific and suitable for sensitive…

The correct answer is Option (2) → Their narrow-spectrum insecticidal application

Baculoviruses are pathogens that attack insects and other arthropods. Most of those used in biological control belong to the genus Nucleopolyhedrovirus. They are species-specific and narrow spectrum: they kill the target insect pest but harm no plants, mammals, birds, fish or even non-target insects. That makes them safe where useful insects are being protected, as in integrated pest management (IPM), or where an ecologically sensitive area is being treated.

Option (1) Their ability to infect all insect species — Incorrect. This is the opposite of the truth. A virus that infected all insects would also kill helpful insects. Baculoviruses act on particular species only.

Option (2) Their narrow-spectrum insecticidal application — Correct. A narrow-spectrum insecticide acts only on the target pest, so baculoviruses leave the rest of the ecosystem unharmed.

Option (3) Their rapid effect on plant pathogens — Incorrect. The biocontrol agent used against plant diseases is the fungus Trichoderma. Baculoviruses attack insects and other arthropods, not plant pathogens.

Option (4) Their ability to fix nitrogen in the soil — Incorrect. Nitrogen is fixed by bacteria such as Rhizobium and Azotobacter and by cyanobacteria. Viruses do not fix nitrogen.

NCERT Extract:
Microbes as Biocontrol Agents – “… Baculoviruses are pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus. These viruses 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.”