Infectious parthenogenesis

Parthenogenesis-inducing Wolbachia bacteria are reproductive parasites that cause infected female wasps to produce daughters without mating(1,2). This manipulation of the host's reproduction enhances the transmission of Wolba chia to future generations because the bacteria are passed on vertically on ly from mothers to daughters. Males are dead ends for cytoplasmically inher ited bacteria: they do not pass them on to their offspring. Vertical transm ission of Wolbachia has been previously considered to be the main mode of t ransmission. Here we report frequent horizontal transmission from infected to uninfected wasp larvae sharing a common food source. The transferred Wol bachia are then vertically transmitted to the new host's offspring. This na tural and unexpectedly frequent horizontal transfer of parthenogensis-induc ing Wolbachia intraspecifically has important implications for the co-evolu tion of Wolbachia and their host.