A large and diverse number of insects harbor maternally inherited symbionts. These symbionts often play important ecological roles in their insect hosts. One class of these symbionts manipulates its host’s reproduction in order to increase its transmission. Wolbachia is the most well-known of these reproductive manipulators, occurring in approximately 20% of all insect species. Wolbachia and a lesser known bacterium, Cardinium, are the only two bacteria known to cause cytoplasmic incompatibility (CI). In CI, uninfected females produce few or no progeny when mated to infected males. We examined CI induced by Cardinium in the parasitic wasp Encarsia pergandiella. The level of incompatibility induced by Cardinium was compared between wasp cultures collected in the field in 2003 and 2006. The strength of CI was found to be similar between the two wasp cultures and appears to be weaker than that observed in earlier studies.

Little is known about how CI invades in a novel population. We used population cages with varying initial infection frequencies to test a model of CI invasion. The model predicts the infection will not spread when the starting infection frequency is below a critical invasion threshold. Infection frequencies in each cage were monitored for a period of four months (8 generations) using diagnostic PCR. The fit of the results to the predictions will be discussed.