Data on diversity are fundamental to our understanding of both natural and disturbed ecosystems. Yet, despite their real and potential importance, knowledge of the diversity of non-pterygote soil arthropods in Canada still is very incomplete. This is illustrated with information on diversity from nine non-pterygote arthropod taxa: Tardigrada, Chilopoda, Diplopoda, Symphyla, Pauropoda, Protura, Collembola, Pseudoscorpionida, and Oribatida, and faunal lists are given for six of these taxa. Although valuable family and generic keys have been published recently, few monographic works or user-friendly keys to species are available. Autecological information essential to explaining the functional role of soil arthropods remains inadequate. Fortunately, the needs of other disciplines and issues are causing a change. For example, current ecological research recognizes that the roles of soil arthropods in decomposition, nutrient cycling, and soil formation are more complex than previously supposed, palaeoecologists require new or corroborating data to interpret their fossil assemblages, and issues such as agroecosystem management, environmental indicators, and global change require a more thorough knowledge of soil communities. Researchers in these areas face poor data on diversity based on inadequate systematics, which limit their understanding of the composition and organisation of soil arthropod communities. This inadequacy presents both a challenge and an opportunity to soil arthropod systematists and ecologists.

The diversity of the Canadian insect fauna decreases and its composition (at all taxonomic levels) changes as climates become progressively more harsh toward the north. This climatic trend dominates patterns of diversity, but many other factors interact to produce the observed patterns. In the arctic, species richness is greatest in the west. Farther south, overall species richness is greatest in the west (especially British Columbia), associated with coastal and cordilleran habitats, and to a somewhat smaller degree in the southeast (especially Ontario), associated with deciduous forests and particularly with transitional forests which occupy a large area of southeastern Canada. However, certain taxa are better represented in the west or in the east, depending on present-day habitats and on historical factors. These conclusions, based chiefly on a sample of taxa of different types, are possible only because basic systematic work has been carried out to distinguish and map the species. Preliminary data on numerical patterns, such as the numbers of species relative to different potential resources such as host plants in different zones, tend to suggest that the occurrence of species in the north may depend so heavily on climatic factors that potential resources are not fully exploited and the effects of interspecific interactions on diversity are reduced.

This paper outlines the known distribution of eight xeric grassland-adapted species of Lygaeidae, and examines these distributions with respect to the glacial history of North America during the Pleistocene, and past and present distribution of grassland vegetation. Four of these species (Neosuris castanea, Sisamnes claviger, Ligyrocoris latimarginatus, and Melanopleurus perplexus) probably survived the Pleistocene in refugia south of the Late Wisconsinan ice sheet. Differences in climatic requirements may explain the variations in geographic distribution exhibited by these four insects and a methodology for testing this is discussed. The four other species (Crophius ramosus, Kolenetrus plenus, Slaterobius insignis, and Emblethis vicarius) may have occurred in the north prior to 1.2 mya and survived the Late Pleistocene in both the northern Beringian refugium and in southern refugia. Molecular systematics, especially use of DNA restriction site or sequence data, might provide the evidence needed to test historical biogeographic postulates based on the extant distribution of these species.

A review of the New World Aenigmatiinae shows that only one of the five Neotropical Region genera currently classified in this subfamily, Cyrtophorina, could belong in a monophyletic group with the type genus Aenigmatias. The first known male specimens of Borgmeieriphora, Colyeria, and Melittophora are described. Based on the structure of the males, these three genera, referred to as the Melittophora-group of genera, belong in the subfamily Metopininae, and are related to the Apocephalus-group of genera. Three new species of Borgmeieriphora are described: B. multisetosa from Costa Rica; B. greigae from Costa Rica; and B. leptotarsa from Panama. Based on observations of two species, adults of Borgmeieriphora are associated with, and may be parasitoids of, army ants of the genus Eciton. Cootiphora gen.nov., represented by the type species C. angustata sp.nov. from Ecuador, is described and is placed in the Melittophora-group. A reconstructed phylogeny of the Melittophora-group of genera is given, showing their hypothesized relationships: Colyeria is the adelphotaxon (= sister-group) of Borgmeieriphora, whereas the relationships among Melittophora, Cootiphora, and Colyeria + Borgmeieriphora are unresolved. Within Borgmeieriphora, B. multisetosa and B. greigae are adelphotaxa, whereas B. kempfi is the adelphotaxon of B. multisetosa + B. greigae, and B. leptotarsa is the adelphotaxon of all other species. The relationships of Platydipteron, another potential member of the Melittophora-group, are unknown. Examination of males of representative aenigmatiine genera from other zoogeographic regions shows that they may belong in a monophyletic group with Aenigmatias. Convergence between true aenigmatiine genera and Melittophora-group genera is based on the shared, limuloid body form, which is probably a defensive adaptation for living in social insect nests.

Adaptations and attributes of gall-inducing cynipid wasps are reviewed to emphasize that differences in life cycles and anatomical features of their galls are just as useful for systematic purposes as are structural differences in the adult insects themselves. The extent to which cynipid wasps have specialized is illustrated by the genus Diplolepis, all species of which are restricted to native and introduced roses and induce structurally distinct galls. Various aspects of Diplolepis biology including life cycles, host specificity, and gall development and anatomy are reviewed. The biologies of two species of Diplolepis that commonly co-exist in the same habitat in central Ontario are then examined in detail. Diplolepis polita (Ashmead) induces a single-chambered gall on the leaves of Rosa acicularis Lindl. whereas Diplolepis spinosa (Ashmead) induces a multi-chambered gall on the stems of Rosa blanda Ait. Differences in life cycles, distribution, host and organ specificity, oviposition, gall initiation and development, along with differences in the communities of parasitoids and inquilines attracted to the galls, confirm the existence of distinct species and allow some speculation on their ecological and phylogenetic relationships.

The groundplan structure and homologies of the mesothoracic pleurosternum of Hymenoptera are postulated using the subcoxal theory of the origin of the pterothoracic pleura of insects, and the cryptosternite theory of an invaginated sternum in most holometabolous insects, based on a comparison of the skeletomusculature of Xyelidae (Hymenoptera) and Raphidiidae (Neuroptera). The following are hypothesized for Hymenoptera: (1) the mesosternum is invaginated except for the prepectus, which is a detached remnant of the presternum; (2) lines that delineate ventral regions on the mesepisternum of many Symphyta are secondarily evolved sulci and arc not pleurosternal sutures; (3) a basalar cleft and an anepisternum are present in the groundplan structure; (4) in Hymenoptera other than Xyelidae the basalar cleft and anapleural cleft intersect so the anepisternum is detached as a separate sclerite, the postspiracular sclerite; (5) the pre-episternum is enlarged secondarily at the expense of the katepisternum, resulting in the paracoxal suture and a narrow katepisternum closely paralleling the posteroventral margin of the episternum anterior to the mesocoxa; (6) the mesepimeron is not divided into an anepimeron and katepimeron by a paracoxal suture but in some taxa is divided secondarily into an upper and lower mesepimeron by marks that delineate the line of confluence between different sets of muscles; and (7) the trochantin is absent from the groundplan structure. Postulated homologies support the hypothesis that Xyelidae represent the basal lineage of Hymenoptera but do not support the hypothesis that the rest of Hymenopera had a biphyletic origin from Xyelidae. The study exemplifies the positive feedback relationship between morphology and systematics and demonstrates the necessity of systematics and phylogenctic hypotheses for testing hypotheses of homology derived through comparative morphology. Schematic figures illustrate the subcoxal theory of pleuron origin and the postulated groundplan of the hymenopteran mesopleuron; mesothoracic muscles that were studied to help homologize pleurosternal features between Xyelidae and Raphidiidae are tabulated and skeletomusculature is documented by scanning electron photomicrographs.

Confusion in cutworm systematics pervades every level of their classification ranging from problems in defining them as a monophyletic group to problems with defining species. Classification provides the primary means of communication and prediction and is most effective when names are stable, and the classification is widely accepted and used, and reflects natural relationships. In cutworms, these requirements are not met: cutworm classification is not stable and use of names in different parts of the world is inconsistent; furthermore, the present cutworm classification does not reflect natural relationships. Instability in cutworm classification can be attributed to several factors: inconsistency in characters used to define groupings such as tribes and subfamilies; problems with defining species; and poor communication among workers. Problems with cutworm classification and progress being made in resolving these difficulties are discussed.

A great proportion of biodiversity is accounted for by organisms, particularly insects, intimately associated with plants. Knowing whether ecological or phylogenetic factors chiefly influence the evolution of host plant associations is essential to understanding speciation in, and therefore factors influencing diversity of, phytophagous insects. Through examination of known host plant associations in Curculioninae and comparison with available reconstructed phylogenetic relationships of certain taxa of Curculioninae, little, if any, evidence for cospeciation (parallel cladogenesis) is found. In curculionine taxa where sufficient host plant and/or phylogenetic data are available, weevil species are narrowly to broadly oligophagous; a number of related weevil species are associated with a single host plant species; many weevil genera have host plant ranges spanning distantly related plant taxa; and available weevil reconstructed phylogenies are not concordant with plant relationships. Rather, for at least some weevil taxa, evolution appears to be mediated by one or more of a variety of strictly ecological factors, particularly habitat associations. General applications of these results include biological control, pollination biology, conservation and restoration biology, and use of patterns in insect – host plant associations to resolve problems in plant classification.

In swallowtail butterflies of the Papilio machaon species group, mitochondrial (mt) DNA divergence has allowed speciation and adaptation to be understood more precisely. The reconstructed phylogeny of mtDNA of the P. machaon group is largely congruent with prior systematic hypotheses based on allozymes and color pattern. Genetic divergences of mtDNA support use of broad, character-based species concepts for the P. machaon group, and allow inferences regarding the origin of hybrid populations. The mtDNA phylogeny provides a guide for evolutionarily appropriate comparisons in studies of the chemical and genetic basis of hostplant use. Finally, mtDNA demonstrates the phylogenetically distinct status of an endangered species, P. hospiton.

Four emergence series were collected from a small mesotrophic–dystrophic lake in the southern Laurentians of Québec: near shore (station A, 0.3 m, shrubs and heaths), in the littoral zone (B, 0.6 m, and C, 1 m, aquatic vegetation), and in open water (D, 6 m, no vegetation). A gradient of species richness (121–34), of numbers (4622–1120/m2), of diversity (5.62–2.42 bits), and of equitability (0.81–0.48) extended from the shore to the open water. Also recognized was a seasonal succession of early synchronized species, many of which completed a second generation by late summer, and of more dispersed summer species. This pattern was best exemplified in the shore station, whereas in deeper sites, the assemblages were increasingly less structured and dominated by fewer species. Chaoborus punctipennis, a benthic insect feeding in the water column at night, tended to predominate in the outer stations and to impose its particular seasonal dynamics on the assemblage there. Chronological clustering revealed distinctive early- and late-season assemblages in all sites. A succession of distinct and temporally structured mid-season assemblages was evident at the shore station, but this pattern was obscured in other stations because of the recurrence and dominance of the same species throughout. Though these particular patterns may be restricted to the one lake studied, this approach based on a taxonomical and temporal analysis offers promise for generalizations once it has been applied to a variety of lake systems.

Systematics allows the extraordinary diversity of biological systems to be understood, and information about organisms to be organized and made accessible. Key patterns that help to interpret natural processes can be summarized, and biological traits predicted, by determining the relationships of natural taxa. Ecological roles are made visible and existing knowledge is made accessible only through specific names. Most organismic diversity is represented by terrestrial arthropods, but knowledge is very incomplete. Even for species found in Canada, half have not been described and the immature stages of most are unknown.Systematics supports entomology and underpins studies of biology in many different ways. From these roles, understanding is gained about diversity and evolution, distributions and biogeographically significant regions of the country, adaptations as related especially to species interactions and metamorphosis, and the application of systematics information. In addition, the values of basic systematic work, modern techniques, and long-term coordinated efforts in studying the fauna are emphasized.A coordinated study of diversity by systematists in conjunction with ecologists and others is required. Such a coordinated approach is timely given recent recognition that the world depends on self-sustaining but increasingly threatened biological systems. Diverse organisms maintain those systems but can be distinguished only through systematics. Adequate long-term support — for systematics positions, research collections, activities that include the preparation of basic works such as monographs, and educational facilities — is required to underpin the systematics component of such a coordinated study.