Head capsule concavities accommodating the antennal bases in Hymenoptera pupating in wood: Possible emergence-facilitating adaptations

The area around the antennal bases and on the lower face was studied in Hymenoptera, including representatives of all “symphytan” superfamilies and apocritan families pupating in wood. This was done in order to eludicate the possible function and phylogenetic significance of modifications in the area under study. Two different kinds of structure which might serve to accommodate the antennal bases during emergence from the site of pupation, were investigated. Subantennal grooves were observed in Siricidae, Xiphydriidae, Orussidae, Megalyridae, and some Aulacidae, and vestigial grooves are probably present in Stephanidae; possible incipient structures were observed in some Tenthredinoidea, Megalodontoidea and Cephoidea. Antennal scrobes were observed in Ibaliidae, Liopteridae, Ichneumonidae and Chalcidoidea; they might have taken over the function of the subantennal grooves in these taxa. The distribution of subantennal grooves within the Hymenoptera cannot be explained without some homoplasy.