Which of the following is an example of biological control in pest management?

Biological control refers to the use of natural enemies or predators to manage pest populations, making it a sustainable and eco-friendly approach in pest management. Parasitoids, which are organisms that live on or within a host and ultimately lead to the host's death, exemplify this method effectively. By introducing or enhancing the populations of these parasitoids, pest populations can be controlled naturally, reducing the need for chemical pesticides.

Other methods listed, such as the use of screens, heat treatments, and manual pest removal, represent physical or mechanical control strategies or cultural practices rather than biological control. Screens act as barriers to prevent pest entry, heat treatment involves raising temperatures to eliminate pests, and manual pest removal relies on human labor to directly take out pests. While these methods can effectively manage pests, they do not involve the use of living organisms to target pest populations, hence they fall into different categories of pest management.