Cedar oil is used as both a barrier to repel and kill insects and as an insecticide applied directly to insects to kill them. Cedar oil works by permeating pest insects and affecting their pheromones.
Pest insects use pheromones to find food and mates. When cedar oil disrupts this process it causes the pest insects to die relatively quickly, as they are unable to eat or procreate. Beneficial insects are generally not driven by pheromones for their activities, and thus are unaffected by the cedar oil. Cedar oil is applied in either a liquid or gas form, and both are lethal to pest insects if they come in contact with the oil for even a brief period of time.