Atypical transovarial transmission of sex ratio spirochetes by Drosophila robusta sturtevant

The pattern of transmission of Sex Ratio spirochetes to the progeny of Drosophila robusta females that had been injected with spirochete‐laden hemolymph was studied. Males appeared with about the same low frequencies in all the broods, but spirochetes were transmitted in high frequencies only to the early brood progeny, the transmission to later progeny being greatly reduced. This pattern is in striking contrast to that observed in D. melanogaster and D. pseudoobscura females in which males appear in nearly equal numbers along with females in the early broods, when the frequency of spirochete transmission is low, but disappear completely from the later broods, when all the females possess a dense population of spirochetes in their hemolymph. The transmission pattern in D. robusta supports the idea of a separation between the spirochete itself and the factor responsible for male lethality.