Behavioral assays to examine house fly, Musca domestica L., attraction to honeydew

In 2006, an outbreak of Escherichia coli O157:H7 associated with spinach affected over 200 individuals in 26 states. While the cause of this outbreak is inconclusive, the proximity of an animal facility to the spinach field and, consequently, high fly abundance is a risk factor for transmission. Flies can transmit pathogens to leafy greens, such as spinach and lettuce, by depositing feces and regurgitant on the leaves, posing a food-safety risk. Flies are not commonly associated with fresh leafy greens; however, we hypothesize that they may be attracted to the honeydew produced by plant feeders such as aphids and whiteflies. We used a cage bioassay to assess fly preferences towards various honeydew samples, which were collected from throughout California or from laboratory colonies. House flies showed a preference for all the honeydew samples tested except for one. This suggests  the presence of honeydew may lead to increased fly activity in the immediate area, leading to contamination of food crops. Further studies on identifying honeydew volatiles compounds will contribute towards the development of improved “attract and kill” strategies, which will reduce human exposure to insecticides and abates potential insecticide resistance.