Wolbachia Infection in Culex Pipiens does not Alter its Performance in Intraspecific Competition or Interspecific Competition with Aedes Albopictus

Wolbachia is a bacterial symbiont that infects both sexes of many mosquitoes and other insects. To better understand Wolbachia’s possible pest control potential, we are studying ecological effects Wolbachia may have on mosquitoes. Female reproduction is affected by Wolbachia-induced cytoplasmic incompatibility (CI), in which uninfected females produce inviable eggs when mated with infected males, but infected females produce viable eggs when mated with all males. CI causes rapid spread of Wolbachia in a population. Beyond CI, Wolbachia can also affect the host’s physiology and reproduction, and may interfere with the mosquito’s ability to transmit pathogens. We postulate that Wolbachia is a mutualist with its mosquito host and tested the prediction that removing the Wolbachia infection renders the host more susceptible to negative effects of intraspecific and interspecific competition. Our focal species, Culex pipiens, and the interspecific competitor, Aedes albopictus, are both major vectors of human pathogens. Previous work indicates that A. albopictus are superior competitors to C. pipiens. Thus, our specific prediction is that effects of competition on C. pipiens will yield steeper negative relationships of survival to density when C. pipiens is uninfected and less steep negative relationships when C. pipiens is infected. In our experiment, we used larvae of Wolbachia positive (control), Wolbachia negative C. pipiens and a standard population of A. albopictus at its normal state (Wolbachia positive). The larvae of the two species were placed in the same containers at various densities, with each density replicated with both Wolbachia strains. Overall, the presence or absence of Wolbachia had no significant effects on competition for resources between C. pipiens or A. albopictus. Survival to adulthood of C. pipiens was significantly affected by both inter- and instar-specific competition, while A. albopictus survival to adulthood was significantly affected by neither intraspecific nor by interspecific competition. Our experiment also showed that interactions between C. pipiens density or A. Albopictus density and Wolbachia positive/negative were not significant, meaning that the effect of densities on survival of C. pipiens does not depend on the Wolbachia infection. Infected and uninfected C. pipiens responded in the same way, thus, our hypothesis of mutualistic effects on larvae is not supported