Insecticides that target sucking insects do so primarily by what means?

Insecticides that target sucking insects primarily operate through contact absorption. Sucking insects, such as aphids, whiteflies, and leafhoppers, feed on the plant sap by piercing the plant tissues with their specialized mouthparts. When an insecticide is applied to the plant, it can be absorbed through the insect’s outer body layers upon contact. This mode of action is effective because the chemical can interfere with the nervous system or other vital functions of the insect once absorbed.

While stomach poisoning, respiratory damage, and disruption of reproduction are valid modes of action for other insecticides or types of pests, they are less applicable to sucking insects. Sucking insects extract liquids through feeding, meaning they are unlikely to encounter stomach poisons unless they consume a treated leaf. Additionally, their respiratory system does not function in the same way as that of respiratory-breathing insects. Disruption of reproduction is also a more indirect action and not the primary means of controlling sucking pests. Thus, contact absorption is the most direct and immediate method by which these insecticides exert their effects.