Which of the following is an example of biological control?

Biological control involves the use of living organisms to control pest populations and is often a part of integrated pest management strategies. The correct answer refers to birds, insects, fungi, and viruses, all of which can play a significant role in managing pest populations naturally. For instance, certain insects can prey on pest species, while beneficial fungi can infect and reduce populations of harmful pests. Additionally, some viruses can specifically target and disrupt pests, reducing their numbers without harming non-target species or the environment.

Other options represent different pest control methods but do not fall under the category of biological control. Fungicides are chemical treatments designed to eliminate fungal diseases, while mechanical traps physically capture pests. Chemical repellents work by deterring pests, not by directly utilizing biological organisms to control them. Thus, the biological control option effectively highlights the use of natural predators or pathogens to manage pests.