Streptococcal L-forms isolated from Drosophila paulistorum semispecies cause sterility in male progeny.

The Drosophila paulistorum complex contains six semispecies that do not normally interbreed. In the laboratory, crosses between semispecies produce fertile daughters and sterile sons. Microbial endosymbionts have been observed in all D. paulistorum flies that display this male sterility. Streptococcal L-forms have been isolated from the Andean-Brazilian (Mesitas) and Transitional (Santa Marta) semispecies and cultured in artificial medium. Transfer of these L-forms from their native hosts into reciprocal semispecies resulted in sterile male progeny. When L-forms were inoculated into the semispecies from which they had been isolated, most of the male progeny were fertile. Control streptococcal L-forms did not show this sterility pattern.