|Infraorder:||Aculeata (but see text)|
The name Aculeata is used to refer to a monophyletic lineage of Hymenoptera. The word "Aculeata" is a reference to the defining feature of the group, which is the modification of the ovipositor into a stinger (thus, the group could be called stinging wasps, though the group also contains the ants and the bees). In other words, the structure that was originally used to lay eggs is modified instead to deliver venom. Not all members of the group can sting; a great many cannot, either because the ovipositor is modified in a different manner (such as for laying eggs in crevices), or because it is lost altogether.
This group includes the bees and ants and all of the eusocial Hymenopterans. It is commonly believed that the possession of a venomous sting was one of the important features promoting the evolution of social behavior, as it confers a level of anti-predator defense rarely approached by other invertebrates.
The use of the name Aculeata has a long history at the rank of infraorder or division, and it is only with the advent of modern phylogenetics that the higher classifications of insects (and other organisms) have come to reject artificial (paraphyletic) grouping categories. While the Aculeata is a good natural group, containing all the descendants of a single common ancestor, the supposed "other infraorder" of the Apocrita - the "Parasitica" or "Terebrantia" - is not a natural group, just as the "sawflies", the basal lineages of Hymenoptera, are not.
The Aculeata are therefore maintained as a taxon, either at infraorder or division rank or as an unranked clade. However, the "Parasitica" must be considered a paraphyletic assemblage; the taxon "Parasitica" is discarded and their interrelationships are subject of further study. Provisionally, they all can be treated as superfamilies incertae sedis in the Apocrita, without being placed in an infraorder. It is highly likely that at least some of these parasitic wasps - for example the Stephanoidea - are as closely related to the Aculeata as to other "Parasitica".
On the other hand, among the parasitic wasps the Ichneumonoidea seem particularly closely related to the Aculeata. If taxonomic ranks are used, it may therefore be best to treat the latter as a division and divide the Apocrita into some 6 infraorders representing lineages of about equal standing, one of which would unite the Aculeata and the Ichneumonoidea.
Note that having the same taxonomic rank does not imply equal evolutionary standing, whereas placement in the same higher-ranked taxon ideally does, or at least implies that regardless of what specific rank they have, the lower-ranked taxa are all part of the same evolutionary radiation. Therefore, would the Aculeata and the Ichneumonoidea be placed in an infraorder, the former would still be considered a division and the latter a superfamily. Despite having different ranks, they would be members of the same taxon and sister lineages.
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