What must a pesticide do in order to be effective against pests?

For a pesticide to be effective against pests, it often needs to be ingested by the pest. Many pesticides are designed as stomach toxins; when a pest consumes the bait or treated host material, the active ingredients disrupt the pest's biological functions, ultimately leading to its demise. This method of action is advantageous as it targets pests who typically feed on plants or stored food, which makes ingestion a practical route for delivering the toxic agent.

While there are pesticides that work through skin absorption or respiratory exposure, these methods are not universally applicable to all pests and often depend on the pest type and formulation of the pesticide. Therefore, ingestion stands out as a broadly effective criterion for many pesticides, as it encompasses both scenarios where pests actively feed on treated materials.