Stop Mosquitoes from Breeding in Your Birdbath or Pond! Any standing water can breed swarms of mosquitoes, even your birdbath or rain barrel. Our Mosquito Control Rings contain Bt israelensis, a naturally occurring bacterium that kills mosquito larvae for a full 30 days. Each slow-release, floating Control Ring treats 100 square feet of surface area in your pond or water garden. Control mosquitoes naturally Rings last for a month Each ring treats 100 square feet