Bacteria that kills off only male fruit flies

Scientist have been seeing a strange phenomenon that causes male fruit flies (Drosophila) to die. This was noticed during the 50's when they crossed two strains of the same fruit fly together only producing females. The geneticists believed it must have been from a mutation, however from further analysis it is seen now to be the cause of the endo-symbiotic bacteria Spiroplasma Poulsonii that stays inside the blood stream and later passes it onto the offspring from the oocytes. S.poulsonii is very specific in only ending of male embryos. There was no molecular mechanism that causes this yet, it was previously believed that they produce a kind of toxin (androcidin). Then Professor Bruno Lemaitre and Dr Toshiyuki Harumoto from EPFL found the gene named Spaid to encode protein that causes certain structures that localize on the X chromosome of male embryos then increasing the transcription of gene onto it. (1 &2)
Having that females have two XX chromosomes it is now understand why the males do not survive but the females are still able to. (1)
""To our knowledge, Spaid is the first bacterial effector protein identified to date that affects host cellular machinery in a sex-specific manner," says Harumoto. "And it is also, to our knowledge again, the first paper to identify an insect endosymbiont factor causing male killing. As such, we expect that it will have a big impact on the fields of symbiosis, sex determination and evolution."" (1)

references:
(1) Male Drosophila die due to bacteria
(2) paper of male killing toxin in a bacterial symbiont of drosophila