Mosquito Dunks and Mosquito Bits, when wet, release a biological larvicide that is eaten by the baby mosquitoes (larvae). Mosquito larvae that eat the larvicide are dead within 24 hours. These products are effective even after repeated wetting and drying.
Aquabarrel™ suggests that the Mosquito Dunks be used in rain barrels.
Mosquito Dunks also prevent mosquito infestations (the source of West Nile and Eastern equine encephalitis) from developing in other sources of standing water, such as compost piles, rain gardens, bird baths, flower pots, tree holes, water gardens, roof gutters, and animal watering troughs.