...and if you want to eradicate mosquito larvae in a small closed water body, without the use of chemicals, it might be worthwhile to add there dry seeds of shepherd's purse, which in America is an alien plant. It is said (though I haven't yet the time to play with this, so I cannot vouch for it) to release enzymes which dissolve the larvae's covers and in this way obtain (more) nutrients. If it does germinate someplace near your water body, eat young leaves for salad and Feel Avenged:)