What defines systemic insecticides?

Systemic insecticides are characterized by their ability to be absorbed by plants through their roots or foliage and then transported throughout the plant's tissues. This systemic nature allows these insecticides to act effectively against sucking pests, such as aphids and spider mites, which feed on the plant's sap.

When systemic insecticides are employed, they become part of the plant's system, thus safeguarding the entire plant against pest attack, not just the areas where the insecticide is applied. Sucking pests are particularly targeted because they can ingest the insecticide while feeding on the plant, leading to their demise.

In contrast, the other options do not accurately define systemic insecticides. While some systemic insecticides may work against chewing pests, this is not their primary application. Additionally, not all systemic insecticides are exclusively applied to the soil or produced externally; they can vary in application methods and formulation. Understanding this concept is crucial for pest management strategies and ensuring that insecticides are used effectively for the chosen pest targets.