What is the main characteristic of a residual insecticide?

A residual insecticide is defined by its ability to remain active for an extended period after application. This means that once the insecticide is applied to a surface, such as plant leaves, the chemical continues to affect pests that come into contact with it over time. The longevity of its effectiveness is crucial for controlling pest populations, as it reduces the need for frequent reapplications, which can save time and resources.

In contrast, an insecticide that works only when applied directly to pests lacks the residual effect and requires immediate contact for it to be effective. The characteristic of covering a broad range of insects relates more to the spectrum of pests an insecticide can control, rather than its residual properties. Lastly, an insecticide that only affects pests at the surface level does not capture the essence of residual activity, which extends beyond just immediate contact by maintaining efficacy over time.