Larvicides based on Bacillus thuringiensis subsp. israelensis are the instruments of choice for the suppression of nuisance and vector black fly populations. Todays formulations are highly effective in a wide range of habitats and have been repeatedly shown to be safe to nontarget organisms. Multiple studies have demonstrated that long-term black fly suppression programs do not cause significant deleterious effects on higher trophic levels or ecosystem structure. The success of Bti-based larvicides has led to a significant decline in research into other materials that could be used against black fly populations. There are no other active ingredients registered for larval black fly applications in the United States today. Recent research has demonstrated the importance of multiple factors related to larval feeding inhibition and the resulting reduction in larval susceptibility. Continued study of these factors will help guide operational personnel as to when to apply Bti-based larvicides for maximum effectiveness and efficiency.