A contribution to the knowledge of the odonata

Abstract

Theories concerning the origin of insect wings and flight are reviewed and a new scenario for their origin proposed. It is suggested that environmental conditions of the small stream were responsible for the evolution of insect flight, and that thermoregulation as well as respiration was important in the preadaptation of wings. The possibility that the five paired convex-concave vein systems each represented a dorsal-ventral blood channel is suggested. Odonate wing vein homology and nomenclatural systems, and phylogeny are reviewed. The process of vein loss is evaluated in the Palaeoptera and a new system of odonate wing vein homologies proposed. The odonate wing mechanism is analyzed and the heretofore overlooked discal nodus characterized. Reevaluation of the comparative morphology of fossil and recent Odonata indicates that Protozygoptera and Protanisoptera represent evolutionary side branches, that the Anisozygoptera is polyphyletic, and that Isophlebiidae and Calopterygoidea are the most generalized Odonata known. Previous scenarios explaining evolution of the unique odonate copulatory process are reviewed. Considering the copulatory behavior of the Calopterygoidea generalized supports evolutionary trends toward male domination and in-flight completion of the process. Assuming direct sperm transfer the original odonate mode requires that originally oviposition be in tandem and that sperm transfer to and from male anterior abdominal sterna be accidental. In contrast, assuming an original indirect transfer of sperm leads to a copulatory sequence similar to that of the Odonata. The proposed scenario differs from others in that extraordinary postures are not envisioned, the process is completed at rest, and the odonate tandem hold is developed prior to copulation. Anisopteran morphology and phylogeny are reviewed and reliable dentification keys developed for North American families and genera, and for 180 anisopteran species collected in Virginia and vicinity. Each species is described and photographed, including seven new species. The biogeography of Virginia Anisoptera is best explained by overlapping biotic regions, the fauna being a mixture of eastern North American, boreal, and tropical elements. New efficient methods for collecting, preserving, and rearing Odonata are described.