What characterizes systemic poisons in pest control?

Systemic poisons are characterized by their ability to be absorbed into the organism's system, typically through the roots of plants or through the tissues of the pest. When these poisons enter the bloodstream or the internal fluids of an organism, they can affect various physiological processes. This systemic action is what differentiates them from other types of pesticides that may act primarily on contact or ingestion.

In pest control, systemic poisons are particularly useful because they can provide protection throughout the entire plant, making them effective against pests that feed on the plant's tissues. Once ingested by pests, the poison disrupts biological functions, leading to their mortality, but it’s the absorption into the system that is critical for its effectiveness.

Other options refer to mechanisms of action that are more characteristic of contact poisons or fumigants. The immediate action upon contact pertains to contact pesticides, while toxic vapors relate to gaseous fumigants. The ingestion aspect describes how some poisons work but does not capture the systemic nature of the poison, which emphasizes absorption into the blood as a defining characteristic.