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Phylogenetic studies on two different groups of Chalcidoidea were conducted. The subfamily Pteromalinae (Hymenoptera: Pteromalidae) was analyzed using the 28S D2-D5, Cytochrome b and Cytochrome Oxidase II gene regions, with focus on discovering the nearest relatives of the genus Nasonia. No support was found for monophyly of Pteromalinae, perhaps in part because of the low 28S molecular divergence within the group. Both maximum likelihood and Bayesian results indicate that Nasonia renders Trichomalopsis paraphyletic, and that Trichomalopsis sarcophagae is the sister group of the genus Nasonia. Nasonia and T. sarcophagae are both infected by Wolbachia bacteria, suggesting a history of Wolbachia infection that could be older than Nasonia itself. Other clades of Pteromalini that were 100% infected with Wolbachia among sampled species include the Australasian genus Pseudanogmus and Coelopisthia + Diglochis. Support was found for a monophyletic assemblage of taxa historically placed in Miscogasterinae, and the subfamilies Cratominae, Miscogasterinae and Panstenoninae are synonymized under Pteromalinae n. syn. The genus Diconocara is transferred from Pteromalini to Miscogasterini n. stat. based on both molecular and morphological data.

A combined molecular and morphological phylogeny of the family Eulophidae is presented with focus on relationships within the subfamily Entedoninae. The 28S D2-D5 and CO1 gene regions were examined in partitioned maximum likelihood and Bayesian analyses, and an additional Bayes analysis was conducted to oberserve the effect of historically recognized morphological characters on the results. Eulophidae was strongly supported as monophyletic only when the genus Trisecodes was excluded. The subfamilies Eulophinae, Entiinae (=Euderinae) and Tetrastichinae were consistently monophyletic, but monophyly of Entedoninae was supported only in the combined morphological and molecular analysis. The lack of support from the molecular data was likely due to the form of the 3e´ subregion of the 28S D2 rDNA in the nominal subgenus of Closterocerus. The tribe Euderomphalini was excluded from a monophyletic Entiinae, suggesting that it should be retained in Entedoninae. Opheliminae n. stat. is raised from unplaced tribe to subfamily status, and a sister group relationship of Opheliminae + Entiinae was strongly supported. The genera Neochrysocharis n. stat. and Asecodes n. stat. were removed from synonymy with Closterocerus because molecular data corroborate their morphological differences. Closterocerus (Achrysocharis) germanicus was transferred to the genus Chrysonotomyia n. comb. based on molecular and morphological characters.

The posterior surface of the head was examined in several families of Chalcidoidea and interpreted according to theories of head capsule evolution as proposed by Snodgrass. Most chalcidoids have only a hypostomal bridge, but some species in the families Chalcididae, Eurytomidae, Pteromalidae, and Torymidae have postgenal bridges that may have been independently derived. Species of small-bodied parasitic wasps with a reduced head capsule, such as many Aphelinidae, Mymaridae, and Trichogrammatidae, lack important landmarks and cannot be easily interpreted without making inferences from related species. Several features provide potentially useful phylogenetic information, such as the presence of a postgenal bridge, extent of the hypostomal carina, extent of secondary posterior tentorial pits, and form of the mesal lamellae extending from the foramen magnum to the oral cavity. However, in many cases these characters present problems of homology that require a larger phylogenetic context to answer.