You may want to take a look at Mosquito Dunks:
Kills mosquito larvae for 30 days! Mosquito Dunks have been used by professionals for more than a decade and have proven their value in destroying mosquitoes - by killing the larvae before they mature into biting adults.
Made with Bt-israelensis (Bt-i), a highly specific biological pesticide, this product represent a major breakthrough for people and the environment when compared with the traditional toxic chemical approach to mosquito control. Will not harm people, pets, wildlife or fish. To learn more about Bt-i, click here for reference information from the Environmental Protection Agency.
Easy To Use:
Once a month place wherever water accumulates around your home - you'll be rid of mosquitoes for the whole season. Each Dunk will effectively treat up to 100 square feet of surface water regardless of depth. They may also be broken in half to treat smaller areas. Great for use in water gardens, flower pots, bird baths, rain gutters and decorative ponds!
product image http://cache.planetnatural.com/planetnatural/images/large/mosquito-dunks-large.jpg
