Which is an example of a mechanical control method used for forest pests?

The example of a mechanical control method used for forest pests is handpicking larger pests off trees. This approach relies on physical actions to directly remove pests from their environment, thereby reducing their population and minimizing damage to the trees. Mechanical control methods are distinguished by their reliance on non-chemical techniques that actively disrupt pest life cycles or remove pests without altering the ecosystem chemically. Handpicking is a straightforward and effective way to manage larger, visible pests, making it a practical strategy in forest pest control.

In contrast, the other options involve different methods of pest control: chemical sprays depend on the application of synthetic or natural chemicals, releasing natural predators introduces biological agents to prey on pests, and planting resistant varieties enhances plant immunity to pests. Each of these methods serves important roles in pest management but does not fall under the category of mechanical control.