The Musca domestica salivary gland hyperplasia virus (MdSGHV) is characterized by its ability to induce enlarged (hyperplasic) salivary glands in adult house flies. Since summer 2005, a combination of field surveys and pathological studies have demonstrated that the MdSGHV, replicating in the salivary glands, specifically infects M. domestica, is transmitted orally via salivary contamination of food and environment, and occurs in feral house fly populations at rates ranging from 1-30%. Salivary gland hyperplasia is the most apparent symptom of infection, but more importantly, this virus acts as a biological birth control agent on female house flies. Infection shuts down ovarian development and renders females unresponsive to mating. The mechanism underlying the disruption of reproduction appears to function at several levels. Females infected at emergence simply do not produce eggs, reflecting a potential block in vitellogenesis. Analyses of hemolymph protein profiles have shown that the female-specific hexamerin and the yolk protein are not produced in infected females. Potentially, virus infection inhibits the synthesis of salivary enzymes, thus blocking digestive processes required to stimulate the gonadotropic cycle. Alternatively, infected glands may produce signals that interfere with necessary neuroendocrine cues regulating vitellogenesis. When females are allowed to develop eggs prior to infection, the mating responses differ, depending upon when mating is allowed to take place. If the egg-containing females are mated within 24 h of infection, they copulate and deposit a single batch of fertilized eggs. However, if mating is delayed for a longer period, then these egg-containing, virus-infected females refuse to copulate. Both of these results suggest that the virus and/or virally induced signal(s) are acting on the flies’ CNS. To date, there is no evidence of vertical or venereal transmission; survival of the MdSGHV relies upon the continuous release of high numbers of environmentally stable, enveloped virions.