What distinguishes systemic insecticides from contact insecticides?

The key distinction between systemic and contact insecticides lies in how they interact with plants and pests. Systemic insecticides are absorbed by plants and transported throughout their tissues, making them effective in protecting the plant from pests that feed on it. This mode of action allows systemic insecticides to control pests that may not come into direct contact with the pesticide, as they ingest the chemical when they feed on the plant.

This characteristic is particularly advantageous for controlling sap-sucking insects, such as aphids or leafhoppers, which may not be easily targeted by other methods. In contrast, contact insecticides work by affecting pests upon direct contact. Therefore, the effectiveness of contact insecticides depends on the pest making direct contact with the treated surface.

The other choices do not accurately represent the fundamental difference between these types of insecticides:

• Systemic insecticides do not kill on contact; their mode of action is based on absorption and ingestion by the pest.

• The effectiveness of contact insecticides is not inherently lesser; it depends on the situation and pest type.

• Not all systemic insecticides are biodegradable, as this varies based on the specific chemical structure and formulation of the insecticide.

Thus, the absorption of systemic insecticides by plants is the primary reason