A fungus infecting domestic flies manipulates sexual behaviour of its host

The Enomopathogenic fungus Entomophthora muscae infects and kills domestic flies Musca domestica, and rates of transmission are higher at high population densities. I tested whether features of parasitized hosts increased the likelihood of transmission of the fungus in a series of experiments. Individual flies contacting an infected conspecific had a much higher probability of becoming infected than had flies contacting a dead fly without signs of infection. Males especially were attracted to and behaved sexually towards dead, infected flies even when a choice was available between a dead, infected fly and a dead, uninfected individual. The abdomen of infected flies swelled considerably as a consequence of infection, and uninfected female flies with larger abdomens are more fecund than the average female and maybe more attractive. Experiments in which abdomens of infected and uninfected flies were cut off and glued back on other flies demonstrated that the abdomens of infected flies were highly attractive to males. When the size of the abdomen of infected and uninfected individual flies was held constant, infected dead flies were still more attractive than corpses of uninfected flies. This result suggests that features other than the size of the swollen abdomen enhanced the attractivity of infected flies. Features of infected hosts therefore increased the likelihood of transmission of the parasitic fungus.