The smallest in the small: Symbionts in chalcidoidea

Associations with microbes represent major diversifying forces in the evolution of insects. Some critical advancements in our understanding of how symbiotic bacteria shape the biology and evolution of insects have been made in the hyperdiverse Chalcidoidea. These small wasps are often readily cultured and cured of their symbionts, thus serving as ideal experimental systems to elucidate the many interactions and outcomes of symbiosis. All of the major bacterial lineages associated with reproductive manipulation (Wolbachia, Cardinium, Rickettsia, Arsenophonus, Spiroplasma) are present in Chalcidoidea and cause three of the four known reproductive manipulation phenotypes (parthenogenesis induction, cytoplasmic incompatibility, male killing). Here we introduce the variety of effects that bacteria have on their chalcidoid hosts and how they are distributed among taxa. We describe the consequences of symbiont-mediated reproductive manipulation for host reproductive isolation, population genetic structure, the evolution of haplodiploidy and sex determination, behavior, and biologic control, and highlight gaps in our knowledge.