Comparative topography of mesoalinotum and formation of trans-scutal fissure in order Hymenoptera (Hym.)

Abstract

The present work deals with the comparative study of different areas and sutures of the mesoalinotum and formation of trans-scutal fissure in order Hymenoptera. The representatives of the families like Pamphiliidae, Xyelidae, Argidae, Cimbicidae, Diprionidae, Tenthredinidae and Cephidae exhibit a generalized pattern of sutures and areas associated with the mesoalinotum. However, in them the course of the convergent sutures and the prominency of the posterior lobe of the scutellum do not conform to the generalized patterns and differs widely among the representatives of these families. In Siricidae, on the other hand, the convergent sutures are absent, and the prescutum is extremely reduced. In Xiphydridae, the trans-scutal fissure is represented but the posterior lobe of the scutellum is absent. In all the apocritans the trans-scutal fissure is well represented occupying its usual position, whereas, the convergent and the median sutures are absent in them. In wingless formicids and female mutillids the mesoalinotum is secondarily modified to unobtrusively fuse with the surrounding components of the thorax, while in them the trans-scutal fissure remains altogether missing indicating thereby that the occurrence of the fissure is directly related to the incidence of flight.