Old method not old-fashioned: parallelism between wing venation and wing-pad tracheation of cockroaches and a revision of terminology

The Comstock-Needham system, the foundation of main vein homology of insects, is grounded in the comparison between wing venation and wing-pad tracheation, particularly that of Plecoptera and Blattodea. However, the trachea-based approach has come into great dispute in recent years. Meanwhile, the terminology used to describe the wing venation of cockroaches requires a revision according to homology and the practical need. These motivated us to examine the wings of cockroaches, comparing the tracheation of nymphs with the tracheation and venation of adults. We find a correspondence between the tracheation and the main vein venation; therefore the trachea-based approach is effective in cockroaches. It is supported that Neopteran insects have six homologous main veins, namely, Sc, R, M, Cu, Pcu and V. We interpret the wing morphology of cockroaches in detail, including veins, furrows, folds and apical folding. RA and RP in hindwing, ScP, CuA and CuP in tegmen and hindwing, are recognized. Hindwing R+M is the only normal venal fusion in cockroaches. In addition, we propose several descriptive terms: cmv, V[1], V[s], pseudostem and characteristic posterior branch. The venation of 41 species (representing 41 genera), and the wing-pad tracheation of four of them including Diploptera punctata, which has unique apical folding, are illustrated.