Which type of pesticide primarily affects pests through contact with their skin or outer layer?

The primary characteristic of a contact pesticide is that it exerts its effects by coming into direct contact with the organism's external surface, such as the skin or exoskeleton of pests. When these pesticides land on a pest, they penetrate the cuticle or outer layer, leading to toxicity and eventually causing the pest's demise. This mode of action is distinct from systemic pesticides, which are absorbed and distributed throughout the plant or organism, providing protection from within.

Insect growth regulators, while crucial in pest management by disrupting the growth and development of insects, do not primarily operate through direct contact with the pest's outer layer. Similarly, systemic insecticides, which function like systemic pesticides, are taken up by plants or animals and then act internally, rather than relying on exterior contact. This makes contact pesticides especially useful for killing pests quickly upon contact, contributing to their effectiveness in various pest control scenarios.