Female Drosophila melanogaster suffer reduced defense against infection due to seminal fluid components

► Female Drosophila suffer reduced immune defense for at least one day post-mating. ► Mated females demonstrate lower immune gene expression than virgins when infected. ► Lower immune gene expression due to mating correlates with higher bacterial loads. ► Female post-mating immunosuppression is dependent on transfer of seminal fluid. ► Effect of mating on defense depends on proper female germline formation.