How does a systemic insecticide act on a pest?

A systemic insecticide functions by being absorbed into the plant's vascular system, allowing it to circulate throughout the plant tissues. When a pest feeds on the treated plant, it ingests the insecticide, which disrupts essential biological processes within the pest, ultimately leading to its death. This mechanism is particularly effective because it targets the pest at its source of food, ensuring that the insecticide reaches its intended target efficiently.

The other options convey different modes of action that do not apply to systemic insecticides. For instance, the idea of suffocating the pest on contact refers to contact insecticides, which work by affecting pests immediately upon physical contact without needing ingestion. Creating a barrier is characteristic of barrier insecticides designed to prevent pest entry into a certain area without directly affecting them internally. Finally, the notion of repelling pests without harming them aligns with repellent substances rather than systemic insecticides, which are intended to kill pests through ingestion rather than merely keeping them away.