Insect microbe associations are diverse, widespread, and influential. Among the fitness effects of microbes on their hosts, defense against natural enemies is increasingly recognized as ubiquitous, particularly among those associations involving heritable, yet facultative, bacteria. Protective mutualisms generate complex ecological and co-evolutionary dynamics that are only beginning to be elucidated. These depend in part on the degree to which symbiont-mediated protection exhibits specificity to one or more members of the natural enemy community. Recent findings in a well-studied defensive mutualism system (i.e., aphids, bacteria, parasitoid wasps) reveal repeated instances of evolution of susceptibility or resistance to defensive bacteria...