What is a stomach poison?

A stomach poison is defined as a type of pesticide that is ingested by pests when they eat treated plant material. This mode of action involves the chemical affecting the pest's digestive system once it has been consumed, leading to adverse effects that ultimately result in mortality. Stomach poisons are typically formulated to target herbivorous insects, causing them to stop feeding and die after they have ingested the toxic substance.

In contrast, other options pertain to different mechanisms or characteristics of pesticides. For instance, a chemical that absorbs through the skin refers to systemic pesticides, which can enter through the cuticle rather than through ingestion. Chemicals released into the air as a gas describe vapor-phase pesticides or fumigants, which do not operate by ingestion but rather through inhalation or absorption via respiratory systems. Lastly, poisons that target the nervous system of insects are a class of pesticides known as neurotoxins and act by disrupting neurotransmitter function, rather than through the gut. Thus, the identification of a stomach poison hinges specifically on its ingestion and digestive action against pests, making the chosen answer the most accurate.