What is a key characteristic of a contact insecticide?

A contact insecticide is specifically designed to target pests through direct physical contact rather than ingestion. This means that the insecticide functions effectively when it is applied directly onto the insect's body, ensuring that the active ingredients can then penetrate the insect’s exoskeleton and disrupt its physiological processes.

This method of action differentiates contact insecticides from systemic insecticides, which are absorbed by plants and must be ingested by the insect to have an effect. Therefore, the characteristic of requiring direct application to the insect is critical to understanding how contact insecticides operate in pest control strategies.

The other options highlight different traits associated with other types of insect control methods or specific scenarios, but they do not describe the essential function of a contact insecticide. For instance, while effectiveness on larvae can be a factor in different pesticides, it does not define contact insecticides exclusively. Similarly, persistence in the environment describes residual insecticides and does not pertain to the immediacy required in contact applications.