An Aculeate Research

Aculeata or stinging wasps include some of the insect taxa with the highest ecological and economic impact such as ants and bees, in addition to other charismatic groups, e.g., gold wasps, velvet ants and spider wasps. They fill vital ecological roles as predators and pollinators, often to the benefit of humankind, although their medical impact is usually detrimental. Furthermore, the occurrence of eusociality among Hymenoptera is restricted to Aculeata, having evolved multiple times within the group. Traditionally, Aculeata have been regarded as the sister group of the Ichneumonoidea, one of the most diverse superfamilies of parasitoid wasps. Two morphological characters, the presence of ovipositor valvilli and distinct propodeal articulating processes, were suggested by Rasnitsyn as synapomorphies in his analysis which, though intuitive, can be regarded as a milestone in the reconstruction of hymenopteran phylogeny. However, Vilhelmsen found the presence of propodeal articulating processes to be widespread among the Apocrita, not restricted to just Aculeata and Ichneumonoidea. Ronquist performed a formal cladistic reanalysis of Rasnitsyns dataset and found moderate support for the ichneumonoid-aculeate relationship, as it was retrieved under implied weighting, but not among the equally weighted most parsimonious trees. Additional moderate support was provided by an early molecular analysis. Furthermore, Vilhelmsen retrieved Aculeata + Ichneumonoidea in their analyses based on morphological data, but again solely under implied weighting. Under equal weighting, the Aculeata were placed as sister group to the remaining Apocrita except Stephanoidea. 

Studies using microCT and histological sectioning are distinctly more costly and time-consuming than studies of the external morphology or skeletal features only, but they can be crucial to scrutinize supposed homologies as well as reveal new ones. An example of the latter are the posterior processes of the tentorium: Since a tubular extension of the tentorium is described from various hymenopteran families and no other insect orders are known to have this structure we assume it to be an autapomorphy of the order. Based on this hypothesis structures such as the postoccipital bridge sensu Vilhelmsen and (at least one pair of the) additional tentorial pits in Ichneumonoidea described and analyzed by Burks & Heraty can be easier understood in context. Though our present study is based on a small taxon sampling and the homology hypotheses discussed remain to be tested in a broader scale, we hope that they will be integrated in the next generation of phylogenetic analyses, helping to refine our picture of the evolution of Hymenoptera.