House flies (Muscadomestica L.) have resisted human attempts to control them since antiquity,and the global problem of fly resistance to conventional insecticides hasresulted in renewed interest in biopesticides as alternative management tools.Entomopathogenic nematodes such as Steinernema and Heterorhabditis spp.and their associated symbionts are virulent for fly larvae in certainsubstrates (e.g., cow manure mixed with soil), but the harsh environmentspresented by poultry and swine manure are inimical to their survival. Entomophthoramuscae is an important natural regulator of fly populations, butconstraints imposed by production, storage stability, and slow kill rate havelimited its use as an operational control agent. Beauveria bassiana hasmany advantages and has been developed into commercial fly control products. B.bassiana is compatible with other biological agents and strains withsuperior kill rates have been identified. Field tests of this pathogen in poultryhouses and calf hutches have been largely positive. New developments in geneticmodification of B. bassiana could lead to new faster-acting biopesticideproducts that are competitive with conventional insecticides. Early researchwith exotoxin-producing strains of Bacillus thuringiensis was promising,but the shift in emphasis to endotoxin-only strains with high activity againstLepidoptera limited discovery of fly-active strains. Surveys have suggestedthat strains with high levels of the Cry1B endotoxin are more virulent thanother strains for muscoid flies. Recent successes with B. thuringiensis var.israelensis on poultry farms suggest that Bti warrants furtherstudy. House fly salivary gland hypertrophy virus (MdSGHV) has the appealingproperty of shutting down reproductive development in adult flies but attemptsto develop infective baits have been hampered by the refractoriness of olderflies to oral infection. Space sprays to treat flies directly may have more potentialfor delivering MdSGHV into fly populations. Essential oils with substantialamounts of 1,8-cineole, pulegone, limonene, and menthol have high toxicityagainst fly adults. Combinations of house fly-active oils (e.g., rosemary,peppermint, pennyroyal mint, blue gum, bay laurel) could be more effective thanproducts that focus on single active constituents. New formulations andpossible use of synergists could increase the efficacy of botanicals for flycontrol.