Aphelinidae Thompson (Hymenoptera: Chalcidoidea) are a biologically diverse family of parasitoids wasps, many of which are used in classical and augmentative biological control of economically impactful pest species, including whiteflies, scale insects, and aphids (Hemiptera: Sternorrhyncha). Historically, the systematics of Aphelinidae formed a Gordian knot: an intractable problem that could not be solved by available methods, due to extreme morphological homoplasy. Next-generation molecular methods have provided the necessary tools to approach Aphelinidae in a meaningful way. Here we develop a robust phylogenetic hypothesis for Aphelinidae and its internal relationship for an exonic anchored hybrid enrichment data set (186 taxa, 740 loci), explored as both nucleotide and amino acids (chapter 2). We find the family, all subfamilies, three tribes, and several major clades to be monophyletic. We propose Coccidae (Hemiptera: Sternorrhyncha) as the ancestral host of the family, and identify five major host shifts within the family. Finally, we propose an early cretaceous origin for the family, placing it congruently in evolutionary time with other major insect radiation events. Using our recovered hypothesis, we revise the classification of Aphelinidae at the family, subfamily, tribe, and generic levels (chapter 3), and we provide a comprehensive review the family and dichotomous key to tribes (chapter 1). Finally, we begin the revisionary taxonomy of monophyletic species-groups of Encarsia Förster, the most speciose genus in the family with 477 described species and an estimated species diversity of ~4000. Here we treat 79 species to revise the Encarsia strenua species-group, and establish 3 additional species groups (E. japonica species-group, E. pulliclava species-group, and E. quercicola species-group). The work presented here establishes the first comprehensive phylogenetic hypothesis for Aphelinidae, provides a modernized cladistic classification, and puts the family of a firm foundation for additional phylogenomics and revisionary taxonomy.
