The most prevalent bacterial infection found in insects comes from a group of materally-inherited symbionts collectively called Wolbachia. The Wolbachia/insect symbiotic relationship can, for the most part, be characterized as reproductive parasitism. As reproductive parasites Wolbachia have the potential to dramatically influence the evolution of their hosts. No where is this more evident than with the monophyletic strain of Wolbachia infecting the wasp genus Trichogramma. For trichogrammatid wasps Wolbachia not only convert eggs destined to become males to functional females, but also allow infected females to clone themselves via thelytokous parthenogenesis. The maternal inheritance of Wolbachia combined with the ability to induce parthenogenesis in trichogrammatid hosts means that the interaction between host nuclear genes and cytoplasmic Wolbachia genes is necessarily intimate and will determine the fitness of both participants- host and parasite. Our experiments with the horizontal transfer of Wolbachia into novel nuclear backgrounds show the fitness consequences of the Trichogramma/Wolbachia symbiosis is not homogeneous across all nuclear/cytoplasmic genetic backgrounds. We discuss the implications of our findings in the context of both the evolutionary ecology of the Wolbachia/Trichogramma symbiosis and the biocontrol application of Wolbachia-infected Trichogramma wasps.