Wing Tracheation in Chrysopidae and Other Neuropterida (Insecta): A Resolution of the Confusion about Vein Fusion

The wings of insects are one of their most prominent features and embody numerous characters and modifications congruent with the variety of their lifestyles. However, despite their evolutionary relevance, homology statements and nomenclature of wing structures remain understudied and sometimes confusing. Early studies on wing venation homologies often assumed Neuropterida (the superorder comprising the orders Raphidioptera, Megaloptera, and Neuroptera: snakeflies, alderflies and dobsonflies, and lacewings) to be ancient among Pterygota, and therefore relied on their pattern of venation for determining groundplans for insect wing venation schemata and those assumptions reciprocally influenced the interpretation of lacewing wings. However, Neuropterida are in fact derived among flying insects and thus a reconsideration of their wings is crucial. The identification of the actual wing venation of Neuropterida is rendered difficult by fusions and losses, but these features provide systematic and taxonomically informative characters for the classification of the different clades within the group. In the present study, we review the homology statements of wing venation among Neuropterida, with an emphasis on Chrysopidae (green lacewings), the family in which the highest degree of vein fusion is manifest. The wing venation of each order is reviewed according to tracheation, and colored schemata of the actual wing venation are provided as well as detailed illustrations of the tracheation in select families. According to the results of our study of vein tracheation, new homology statements and a revised nomenclature for veins and cells are proposed.