What is a common application for systemic insecticides?

Systemic insecticides are specifically designed to be absorbed by plants and transported through their vascular system. This characteristic allows the entire plant, including its leaves, stems, and roots, to be protected from pests. By being taken up into the plant's tissues, these insecticides provide long-lasting effectiveness against insect pests that may feed on the plant.

The ability of systemic insecticides to circulate within the plant means that even insects feeding on hidden or protected parts of the plant can be affected. This internal mode of action is crucial for managing pests that may not be directly reachable by conventional topical insecticides. Thus, option C accurately captures the essence of why systemic insecticides are favored for pest control in many agricultural and horticultural applications.