Which type of pesticide must directly contact the pest to be effective?

The correct choice focuses on contact pesticides, which require direct contact with the target pest to function effectively. These pesticides work by physically adhering to the pest's body upon application. Once in contact, they can either disrupt the pest's nervous system, cause dehydration, or interfere with its normal physiological functions, leading to death or significant harm.

Contact pesticides are typically used for managing pests like insects or weeds that are directly exposed to the application. This direct confrontation is essential because if a pest is shielded from the pesticide—by barriers like plant tissues or soil—it will not be affected, making effective application critical.

In contrast, systemic pesticides are absorbed by plants and can be transported throughout the plant's tissues, making them lethal to pests that may feed on the plant without requiring direct contact with the pesticide. Preventive pesticides are designed to inhibit pests or diseases before they occur, often through protective measures rather than immediate contact. Some fungicides might also operate preventively, targeting pathogen development rather than being directly effective through contact alone.