 Visit rotorooter.com or call 1-800-GET-ROTO. Mosquitoes can transmit deadly diseases, including West Nile virus, but some mosquito dunks kill mosquitoes before they're old enough to bite. Just float an organic mosquito dunk in ponds, birdbaths, rain barrels, and any standing water to kill mosquito larvae for 30 days or longer. Don't worry, mosquito dunks won't harm people, pets, fish, birds, or wildlife.