Experts and BHG readers answer.
Red bugs on lilies
Neem is effective if applied to the undersides of the leaves where the larvae feed, AND if applied while the larvae are small. Begin applications early in the season (by late April), and repeat the applications weekly throughout the growing season.
If you have only a few plants, you can also scout the plants for the larvae and remove them by hand. Otherwise, chemical pesticides such as Orthene or malathion are recommended.