A number of commercially available controlled release organotin molluscicides and their degradation products were evaluated against Culicine larvae as a segment of a broad environmental impact and chemodynamics study. Test materials were observed in periodic bioassay, in some cases for over 400 days, and found effective against mosquito larvae at dosages considered to be practical for field application. The LT100 results were comparable to controlled release temephos and chlorpyrifos. Long term efficacy, low biological persistency (once released from the binding matrix), and the suspected proteolytic kill mechanism which may negate the development of tolerance would indicate that tributyltin fluoride and bis (tri-n-butyltin) oxide in sustained release compounds are suitable as mosquito larvicides.