Mosquito Dunks float on the water and keep on working for 30 days or longer under typical conditions. While floating, they slowly release a long-term, mosquito larvicide, Bacillus thuringiensis var. israelensis (Bt) at the water's surface. The mosquito larvae eat the Bt and which in turns paralyzes their digestive system. The Bt-affected insects die within days from starvation.
I have been buying Bt donuts for years. We have two small ponds and a dry-creek that will puddle here and there. When we first bought our property we were constantly getting swarmed by mosquitoes. There was a noticeable difference after we started to use the Bt with no ill effect to the frogs. They're alive and croaking. Well worth the investment!Review by AccomplishMoreToday (on 3/12/12)