Response of house flies, Musca domestica (Diptera: Muscidae), to denatonium benzoate

House flies are global pests of humans and associated animals and spread a wide range of diseases. House fly control is still mainly achieved via manure management and chemical control. Toxic adult house fly baits remain the most common chemical control option, and these products often include the bittering agent denatonium benzoate (DB), which is added to avoid accidental poisonings. Improved understanding of the taste system of adult house flies can help in developing more effective fly control. DB is unpleasantly bitter to most humans at 10-20 ppm. Insect response to DB varies by species. Ideally, the amount of bittering agent in a bait formulation should be aversive to nontarget organisms, especially children and pets, but not to the pest insect. The concentrations of DB that house flies avoid have not previously been reported. House fly baits that include DB have a DB concentration of 100, or occasionally 20, ppm. House flies from some, but not all strains tested, were found to avoid 100 ppm of DB. Alternative bittering agents were tested, and sucrose octaacetate but not quinine is a promising alternative to DB for use in house fly baits. Tests of natural enemies of house flies are still underway, but DB is not aversive to two species of parasitoids at concentrations used in commercial fly baits. Another concern with any pest control measure is how it may affect the evolution of resistance to the control. We are currently investigating whether house flies readily evolve behavioral resistance to avoid DB.