Baculoviruses are a group of viruses that primarily infect insects. They are used in biological control of insect pests due to their specificity to insects.
Step 1: Analyzing the options.
- Insects (Option 1): Baculoviruses are known to infect various species of insects, such as moths and butterflies, and are commonly used as insecticides.
- Roundworms (Option 2): Baculoviruses do not attack roundworms.
- Molluscs (Option 3): Baculoviruses do not infect molluscs.
- Birds (Option 4): Baculoviruses do not infect birds.
Step 2: Conclusion.
The correct answer is Insects as baculoviruses are pathogens that specifically target insects.
Final Answer:
\[
\boxed{\text{The correct answer is (1) Insects.}}
\]