Sick of mating: sexual transmission of a pathogenic bacterium in Drosophila melanogaster.

Internal fertilization protects gametes from inhospitable environments and ensures sufficient proximity for gamete union. However, close contact between individuals during mating also increases the risk of pathogen transfer. We developed an approach to transfer the entomopathogenic bacterium Serratia marcescens from males to females during courtship and mating in Drosophila melanogaster. We then examined the frequency of contamination and bacterial loads of females copulating with males for varying durations, showing that while courtship is sufficient for bacterial transmission, mating significantly increases the bacterial load received in a time-independent manner. S. marcescens transmission from contaminated males during mating was sufficient to establish rapid, systemic infection and death in mated females.