Phylogenetic implications of the mesofurca in Chalcidoidea (Hymenoptera), with emphasis on Aphelinidae

The skeletomusculature of the mesofurcal–mesopostnotal complex is surveyed within the Chalcidoidea. Four internal character systems are assessed for their phylogenetic significance: the mesofurcal bridge, the structure and position of the furcal–laterophragmal muscle, the structure of the lateral arms of the mesofurca, and the supporting structures for the interfurcal muscles. Among Hymenoptera, Chalcidoidea are unique in having the furcal–laterophragmal muscle attached along the entire length of the laterophragmal apodeme. Also the furcal–laterophragmal muscle originates medial to the junction of the mesofurcal bridge and lateral mesofurcal arm in most Chalcidoidea. Mymarommatidae do not share either of these apomorphic states with Chalcidoidea. Within Chalcidoidea, apomorphic character states were found in each of Aphelinidae, Encyrtidae, Eulophidae, Mymaridae, Rotoitidae, Signiphoridae, Tanaostigmatidae and Trichogrammatidae. For taxa classified as Aphelinidae, the plesiomorphic complement of structures and muscle attachments is retained in Eriaphytinae and Eriaporinae. The mesofurcal bridge is considered to have been lost at least twice in each of Aphelininae and Coccophaginae. Similar interfurcal processes, resulting from loss of the mesofurcal bridge, support the monophyly of Aphelininae (Aphelinini, Aphytini and Eutrichosomellini). Azotinae are placed as the sister group of Aphelininae because of a similar lateral origin of the laterophragmal muscle and the shape of the mesofurcal arms. Other than loss of the mesofurcal bridge, no character states were shared by Azotinae and Coccophaginae. Coccophaginae (Coccophagini and Pteroptricini) are regarded as monophyletic based on the loss of the mesofurcal bridge, the peculiar shape of the mesofurca, and a unique modification of the laterophragmal muscle. Euxanthellus is removed from synonomy with Coccophagus and may be best treated as a separate tribe of Coccophaginae based on the shape of the lateral mesofurcal arms and the presence of a mesofurcal bridge. The shape of the mesofurca suggests a monophyletic grouping of Cales , Eretmocerus and Trichogrammatidae that could render Aphelinidae paraphyletic.