The phylogeny of lower Hymenoptera (Insecta), with a summary of the early evolutionary history of the order

A cladistic analysis of the lower Hymenoptera, including all the ‘symphytan’ families and the apocritan families Stephanidae, Megalyridae, Trigonalyidae, Ibaliidae, Vespidae and Gasteruptiidae, has been undertaken. A total of 98 characters were scored for 21 taxa. Twenty equally parsimonious minimum-length trees were obtained. The phylogenetic status of the Xyelidae is uncertain: they might be monophyletic. or the Xyelinae might be the sistergroup of the rest of the Hymenoptera. The non-xyelid Hymenoptera are probably monophyletic; the phylogeny Tenthredinoidea + (Megalodontoidea + (Cephidae + (Anaxyelidea + (Siricidae + (Xiphydriidae + (Orussidae + Apocrita)))))) is proposed for this clade. The Blasticotomidae are probably the sistergroup of all othe Tenthredinoidea, but tenthredinoid phylogeny is otherwise uncertain. Substantial homoplasy occurs within the ‘siricoid’ families, making the relative positions of the Anaxyelidae and Siricidae uncertain. The Stephanidae might be the sistergroup of the rest of the Apocrita; the phylogeny of the remaining apocritan taxa included is insufficiently elucidated. The phylogeny proposed here supports the hypothesis that the appearance of parasitism in the Hymenoptera took place in the common ancestor of Orussidae + Apocrita, the host of which was probably wood boring insect larvae. The exact larval mode of feeding of the ancestral hymenopteran cannot be determined due ot the diversity of lifestyles in the basal lineages of the order.