Wolbachia are bacteria that are widespread endosymbionts found in more than half of all arthropod species, like all endosymbionts they potentially affect many aspects of their host biology. In particular, many Wolbachia ensure their own transmission to the next generation by selfishly manipulating the reproduction of their host as Wolbachia are primarily transmitted from the host mother to her offspring. This research investigates both short and long-term interactions between hosts and Wolbachia. Specifically, it aims to understand how Wolbachia manipulate host reproduction and how hosts co-evolve to resist these manipulations. The results will be of broad significance to both basic and applied questions in biology. First, given their abundance and effects on their arthropod hosts, endosymbionts including Wolbachia likely contribute to species diversification and broader patterns of biodiversity. The findings will help understand how endosymbionts contribute to the evolutionary and ecological processes that generate and maintain biodiversity. Second, Wolbachia are currently used for biocontrol of insect vectors that transmit human pathogens as well as of agricultural pests that cause harm to plants. The evolutionary dynamics that occur in natural host-endosymbiont interactions likely also occur in engineered biocontrol systems. The findings of this study will inform the potential consequences of wide-scale release of Wolbachia-infected insects, including both how the host evo