Wolbachia Inter-Strain Competition and Inhibition of Expression of Cytoplasmic Incompatibility in Mosquito

Successful field trials have been reported as part of the effort to develop the maternally transmitted endosymbiontic bacteriaWolbachiaas an intervention agent for controlling mosquito vectors and their transmitted diseases. In order to further improve this novel intervention, artificially transinfected mosquitoes must be optimized to display maximum pathogen blocking, the desired cytoplasmic incompatibility (CI) pattern, and the lowest possible fitness cost. Achieving such optimization, however, requires a better understanding of the interactions between the host and variousWolbabachiastrains and their combinations. Here, we transferred theWolbachia wMel strain by embryonic microinjection intoAedes albopictus, resulting in the successful establishment of a transinfected line, HM (wAlbAwAlbBwMel), with a triple-strain infection comprisingwMel,wAlbA, andwAlbB. Surprisingly, no CI was induced when the triply infected males were crossed with the wild-type GUA females or with another triply infected HC females carryingwPip,wAlbA, andwAlbB, but specific removal ofwAlbA from the HM (wAlbAwAlbBwMel) line resulted in the expression of CI after crosses with lines infected by either one, two, or three strains ofWolbachia. The transinfected line showed perfect maternal transmission of the triple infection, with fluctuating egg hatch rates that improved to normal levels after repeated outcrosses with GUA line. Strain-specific qPCR assays showed thatwMel andwAlbB were present at the highest densities in the ovaries and midguts, respectively, of the HM (wAlbAwAlbBwMel) mosquitoes. These finding suggest that introducing a novel strain ofWolbachiainto aWolbachia-infected host may result in complicated interactions betweenWolbachiaand the host and between the variousWolbachiastrains, with competition likely to occur between strains in the same supergroup.