Most larvicides used today are relatively safe to non-targets. Briquets, pellets, granules and water soluble liquids quickly go down into the water column where most fish and other non-targets exist, having greater impact. MMF is completely water insoluble and remains only at the water surface, affecting only a few surface dwellers. While other products quickly settle to the bottom, MMF remains at the water surface.
Midges can be either a concern or a target.
Almost all larvicides used have an effect on midges. Products that go down into the water column, especially bti's, only affect midge larvae rather quickly. Surface films, on the other hand,only affect the developing midge population during the short time they pupate to the surface. Ask the manufacturer to supply complete documentation on non-target testing. Some products such as bti's can be rendered ineffective by UV sunlight.