When neem is applied to a plant it serves as a repellent, but if it is ingested, the compound affects insect egg laying and growth. It rarely causes any irritation to the skin or mucous membranes. It has been used in India and Asia as a cleaner, disinfectant and medicinal. Recent field trials have not confirmed significant repellency activity. However, good control of insects can be achieved if the insects are exposed while they are actively growing immatures - nymphs and larvae.
Action can be slow because the insect often has to go through a molt or two.