Pathogenicity of cultivatedDrosophila willistoni spiroplasmas

Abstract

A transovarially transmitted spiroplasma, the sex ratio organism (SRO), found in the hemolymph of females of four Neotropical species ofDrosophila, acts through an unknown mechanism to eliminate males from the progenies of these females. However, because the SROs were noncultivable, proof of pathogenicity had relied on inoculations from flies. Recently, theDrosophila willistoni SRO (WSRO) was cultured, first in medium containing an insect cell line, then in the medium alone. Injections of cultivated WSROs into normalD. pseudoobscura females resulted in the elimination of males from the progenies of the injected females. In vitro cultures of SROs were re-established from hemolymph collected from females that had been injected with the triply cloned strain (DW-1). Continued passage in cell-free medium has led to a strain that, although male-lethal, is not transovarially transmitted.