Status of biopesticides for control of house flies

House flies (Musca domestica L.) have resisted human attempts to control them since antiquity, and the global problem of fly resistance to conventional insecticides has resulted 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 certain substrates (e.g., cow manure mixed with soil), but the harsh environments presented by poultry and swine manure are inimical to their survival. Entomophthora muscae is an important natural regulator of fly populations, but constraints imposed by production, storage stability, and slow kill rate have limited its use as an operational control agent. Beauveria bassiana has many advantages and has been developed into commercial fly control products. B. bassiana is compatible with other biological agents and strains with superior kill rates have been identified. Field tests of this pathogen in poultry houses and calf hutches have been largely positive. New developments in genetic modification of B. bassiana could lead to new faster-acting biopesticide products that are competitive with conventional insecticides. Early research with exotoxin-producing strains of Bacillus thuringiensis was promising, but the shift in emphasis to endotoxin-only strains with high activity against Lepidoptera limited discovery of fly-active strains. Surveys have suggested that strains with high levels of the Cry1B endotoxin are more virulent than other strains for muscoid flies. Recent successes with B. thuringiensis var. israelensis on poultry farms suggest that Bti warrants further study. House fly salivary gland hypertrophy virus (MdSGHV) has the appealing property of shutting down reproductive development in adult flies but attempts to develop infective baits have been hampered by the refractoriness of older flies to oral infection. Space sprays to treat flies directly may have more potential for delivering MdSGHV into fly populations. Essential oils with substantial amounts of 1,8-cineole, pulegone, limonene, and menthol have high toxicity against fly adults. Combinations of house fly-active oils (e.g., rosemary, peppermint, pennyroyal mint, blue gum, bay laurel) could be more effective than products that focus on single active constituents. New formulations and possible use of synergists could increase the efficacy of botanicals for fly control.