What happens if insecticidal soaps are applied and allowed to dry on insects?

When insecticidal soaps are applied to insects, their effectiveness relies on being in contact with the pests while wet. These soaps work by penetrating the insect's outer shell, disrupting their outer membranes, and ultimately causing their cells to break down, leading to dehydration and death. If the soap dries on the insects before they can be affected, it loses its ability to penetrate their protective barriers effectively. Therefore, allowing the soap to dry means that it will not be able to kill the insects, as its mechanism of action depends on remaining wet during the critical time needed to affect the pests.

Insecticidal soaps are specifically formulated to target soft-bodied insects like aphids and spider mites, and their effectiveness diminishes significantly once dried. Thus, for the application to be successful, the soap must remain on the insects long enough to achieve its desired effect, highlighting why the statement that they do not kill the insects when dried is correct.