Mosquito Dunks for garden water
Bti works only on larvae that eat it, so pupae already in the water still emerge, and larvae that hatch after treatment may partly develop before dying — the Dunks label says to allow at least 48 hours. A Dunk floats and releases Bti for 30 days or more and can be broken up for a bird bath or rain barrel; Bits kill within 24 hours but last up to 14 days. The Dunks label allows fish habitats, the Bits label water with fish, aquatic life and plants; neither goes in treated drinking water. Emptying or screening the water beats either.
Before you order
A bacterium sold two ways: as Gnatrol, watered into compost for fungus gnats, and as Mosquito Dunks and Bits for rain barrels, bird baths and ponds. Larvae that eat it stop feeding and die. It does nothing to adult gnats or mosquitoes, and UC IPM says it is toxic only to fly larvae. How it works, how to tell it has established and the supplier list are on the full Bacillus thuringiensis israelensis profile.
Other controls for mosquito larvae
No other reviewed control is listed for this pest yet.