7. Insect systematics: phylogeny and classification
Because there are so many guides to the identity and classification of birds, mammals, and flowers, it is tempting to think that every organism in the living world is known. However, if we compared different books, treatments will vary, perhaps concerning the taxonomic status of a geographical race of bird, or of the family to which a species of flowering plant belongs. Scientists do not change and confuse such matters perversely. Differences can reflect uncertainty concerning relationships and the most appropriate classification may be elusive. Changes may arise from continuing acquisition of knowledge concerning relationships, perhaps through the addition of molecular data to previous anatomical studies. For insects, taxonomy — the basic work of recognizing, describing, naming, and classification — is incomplete because there are so many species, with much variation.
The study of the kinds and diversity of organisms and their inter-relationships — systematics — has been portrayed sometimes as dull and routine. Certainly, taxonomy involves time-consuming activities, including exhaustive library searches and specimen study, curation of collections, measurements of features from specimens, and sorting of perhaps thousands of individuals into morphologically distinctive and coherent groups (which are first approximations to species), and perhaps hundreds of species into higher groupings. These essential tasks require considerable skill and are fundamental to the wider science of systematics, which involves the investigation of the origin, diversification, and distribution, both historical and current, of organisms. Modern systematics has become an exciting and controversial field of research, due largely to the accumulation of increasing amounts of nucleotide sequence data and the application of explicit analytical methods to both morphological and DNA data, and partly to increasing interest in the documentation and preservation of biological diversity.
Taxonomy provides the database for systematics. The collection of these data and their interpretation once was seen as a matter of personal taste, but recently has been the subject of challenging debate. Entomological systematists have featured as prominent participants in this vital biological enterprise. In this chapter the methods of interpreting relationships are reviewed briefly, followed by details of the current ideas on a classification based on the postulated evolutionary relationships within the Hexapoda, of which the Insecta forms the largest of four classes.