Reduced competitive ability due toWolbachiainfection in the parasitoid waspTrichogramma kaykai

Several hymenopteran parasitoids are infected with parthenogenesis‐inducing (PI)Wolbachia. Infected wasps produce daughters instead of sons from unfertilized eggs. Thus far, little is known about the direct effects of PIWolbachiaon their host's fitness. Here, we report reduced competitive ability due toWolbachiainfection in a minute parasitoid wasp,Trichogramma kaykaiPinto and Stouthamer (Hymenoptera: Trichogrammatidae). Immature survival of infected individuals in a host parasitized by a single infected female, laying a normal clutch of eggs, was lower than those parasitized by a single uninfected individual. When the offspring of infected and uninfected females shared the same host, the infected immatures had significantly lower survival rates than their uninfected counterparts. The survival rate of infected immatures was higher when they competed with other infected immatures from a different infected parent than in competition with uninfected immatures of conspecific wasps. Thus, the hostTrichogrammacan suffer a substantial reduction in fitness when it is infected with the PIWolbachia. We discuss why such a reduction is to be expected when populations of infected and uninfected individuals co‐occur, and how the reduced competitive ability of PIWolbachiainfluences the spread of the bacteria in the field.