D3230: Can house flies taste bitter?

House flies, Musca domestica, are a great nuisance to humans and can transmit numerous pathogens. Fly management is achieved via manure management, chemical control, and biological control. Insecticide formulations used against house flies contain an active ingredient (what kills the fly), a fly pheromone and a phagostimulant. Some of the commercial baits also contain a bittering agent to keep non-targeted organisms away. The bittering agent that is used is denatonium benzoate (DB) at 100 ppm. A bittering agent in an insecticide should be aversive to non-target animals but not to pests. This research focuses on what concentrations of DB are aversive to house flies and whether flies show aversive behaviors to alternative bitter compounds like quinine and sucrose octa-acetate. Chemically, DB resembles quinine, and sucrose octa-acetate is used in pesticides as a bitter additive. Testing the response of flies to bitter will improve understanding of the fly taste system and will help create effective baits.

Proboscis extension response (PER) and consumption were tested for 0, 10, 100 and 1000 ppm of DB in 10% sucrose solutions. Male flies showed significantly lower PER and consumption to 100 and 1000 ppm of DB, whereas females showed significantly lower PER and consumption to 1000 ppm of DB only. Consumption was also tested to observe whether the response of flies to quinine and sucrose octa-acetate is similar to that of DB. Both males and females showed a significanly lower consumption at 100, 500, and 1000 ppm of quinine but not for sucrose octa-acetate.