What type of insecticide acts through the insect feeding on treated plants?

The correct choice, systemics, refers to a category of insecticides that are absorbed by plants and move throughout their tissues. When insects feed on parts of these treated plants—such as leaves, stems, or roots—they ingest the insecticide. This method allows for effective pest control, especially for insects that are difficult to target with surface treatments.

Systemic insecticides are particularly useful for dealing with sap-sucking pests, like aphids and whiteflies, as they infiltrate the plant's vascular system and remain active for an extended period. This not only protects the plant from direct feeding damage but can also disrupt the growth and reproduction of the pests, leading to their eventual death.

In contrast, contact insecticides rely on direct application to the pests themselves, which means they are less effective when the insect is protected by plant tissue. Insect growth regulators modify the development of insects but do not act through direct poisoning from plant consumption. Organochlorines, while effective against various insects, primarily work through contact or ingestion, but are not absorbed systemically in the same way as systemic insecticides. Thus, the definition and mechanism of systemics make them the correct answer to the question regarding insecticides that act through insect feeding on treated plants.