What type of insecticide contacts insects where they are likely to walk?

The correct choice is residual insecticide. This type of insecticide is designed to remain effective on surfaces for an extended period of time, allowing it to kill insects that come into contact with it after application. Because residual insecticides adhere to surfaces such as walls, floors, and other areas where insects are likely to walk, they are particularly effective for preventing infestations and controlling existing populations over time. This long-lasting effect means that even if insects walk over treated areas hours or days later, they can still be affected by the insecticide.

Contact insecticides, on the other hand, require insects to come into direct contact with the spray or a treated surface at the time of application to be effective. Systemic insecticides are absorbed by plants and affect insects that feed on them rather than relying on surface contact. Aerosol insecticides are often used for quick knockdown of insects but may not have the same long-lasting residual properties that allow for extended pest control.