Which of the following best describes the action of insecticides?

The action of insecticides is best described as poisons that control insect populations. Insecticides are specifically formulated chemical compounds designed to target and eliminate insects that can be harmful to crops, livestock, and even human health. They work by disrupting vital biological processes in insects, leading to their mortality. This targeted action is crucial in pest management, allowing for the reduction of insect populations that can damage agricultural products or spread diseases.

The other options do not accurately capture the primary function of insecticides. Fertilizers, for instance, are substances that enhance plant growth by providing essential nutrients, which is unrelated to pest control. Similarly, products that enhance plant growth or act as natural repellents serve different agricultural purposes and do not fit the definition of insecticides, which are primarily focused on the direct elimination of pests rather than promoting growth or acting as a deterrent.