I have no experience with the product that you are talking about, but I really do believe that as long as you are not allowing the water in the birdbath to sit stagnant for several days (I would think at least a week or more) then you are not going to be having mosquitos hatching in the water. I am under the impression and also from the experience of having a birdbath and spraying it with fresh water every few days, that mosquitos need still water to be able to lay eggs and hatch. As long as you are spraying fresh water and probably also spraying hard enough to spill the old water over the edge, then you are going to be perfectly safe and don't need to take the risk of using any kind of chemical and having possible harm coming to anything whether it be the neighbour's cat or dog or the birds or insects which will come to drink.

The BTi in mosquito dunks is a naturally occurring bacterium that is specific to gnat and mosquito larvae. It does not affect other insects or wild life - you can use it without harming bees, and with a clear conscience.

As morz8 states, the Bt is safe, but so, too, as greylady states, you wont need it. Most mosquitoes need about 10 days in still water to hatch, grow and buzz off.

tj

There is a variety of BT that is used by corn farmers to control the corn borer. That has also been blamed for the decline in the monarch and many other butterflies.
But mosquito dunks contain a different strain fo the BT agent called BTi which, they sayAs has been said, mosquitoes don't hatch over night or even in 3 days....but I have noticed that mosquitoes seem to buzz around containers of still water....so you may fine they are invading your little space even if you don't allow them to breed.
Perhaps a little pump and a way to make the water move will deter them? As well as the dunks...
Linda C

that strain of BT (israilensis)(sp) is also very effective on fungus gnats. I keep a 5 gal bucket of water with 2 or 3 dunks floating around, and use that to water plants that have gnats. Two or three times, they're finished.

Compared to buying gnatrol or something similar, at $25 a quart.