Drosophila simulans strains infected with three different Wolbachia strains were generated by experimental injection of a third symbiont into a naturally double-infected strain. This transfer led to a substantial increase in total Wolbachia density in the host strain. Each of the three symbionts was stably transmitted in the presence of the other two. Triple-infected males were incompatible with double-infected females. No evidence was obtained for interference between modification effects of the different Wolbachia strains in males. Some incompatibility was observed between triple-infected males and females. However, this incompatibility reaction is not a specific property of triple-infected flies, because it was also observed in double-infected strains.
Rousset, F., Braig, H., & O'Neill, S. L. (1999). A stable triple Wolbachia infection in Drosophila with nearly additive incompatibility effects. Heredity, 82, 620 - 627. https://doi.org/10.1046/j.1365-2540.1999.00501.x