Comparative morphology of tergal phragmata occurring in the dorsal thoraco-abdominal junction of ditrysian Lepidoptera (Insecta)

Abstract 

A comparative SEM investigation of the transphragma representing the medioanterior margin of the first abdominal tergum in ditrysian Lepidoptera resulted in the establishment of a directed transformation series of gradual modifications. Most remarkably, an additional phragma, for which the term euphragma is proposed, must be assigned to the ground pattern of the Obtectomera. However, this assumption implies that a subsequent loss of the euphragma must be attributed to the ground patterns of the Axiidae, Copromorphoidea, Doidae, Papilionidae and the Hedylidae. On the other hand, a typical euphragma is also observed in the non-obtectomeran superfamily Sesioidea. Similarly, the phylogenetic significance of the presence of a much smaller circular phragma in the Choreutidae is not yet understood. Either the three taxa (Obtectomera, Sesioidea and Choreutidae) constitute a clade, and secondary modifications have obliterated the euphragma on a number of occasions, or the euphragma has been developed independently on more than one occasion. Potential autapomorphies of various subordinate taxa are also discussed.