Studies of Quaternary age Coleoptera fossils from North America and Europe plus recent analyses of insect fossils from late Tertiary (Miocene and Pliocene) sites in northern Canada, Alaska, and eastern Siberia show that many of the species composing the present Canadian insect fauna probably evolved during the Tertiary. Thus the history of Tertiary land bridge links between North American and adjacent continents is pertinent for a discussion of the present Canadian insect fauna.

Movement of lithosphere plates has contributed directly to the emergence and foundering of Tertiary land bridges in three key areas: Beringia, the North Atlantic, and Middle America.

A land bridge probably connected Siberia and Alaska in the Beringian region for most of the Tertiary. During the Eocene its climate was such as to allow exchange of tropical to subtropical adapted plants and animals. Paleobotanical evidence suggests that the Beringian area never supported the type of mixed-mesophytic forests called for by the Arcto-Tertiary concept. By the mid-Miocene much of the region north of 65° was probably a rich coniferous forest. Lowland tundra undoubtedly exited on the fringes of Beringia as early as the Pliocene.

Two and possibly three land bridges connected Greenland and Northern Europe during the Tertiary. The DeGeer bridge joined northern Greenland and Norway prior to the opening of the Greenland Sea in the late Eocene – Early Oligocene. The Greenland-Faeroes bridge was never more than a causeway along the route of the submerged ridge now occupied by Iceland. However it persisted longer, possibly existing as a chain of islands as late as the Miocene. A third land bridge may have connected Labrador and Rockall Bank near England during the Paleocene and early Eocene. The climatic history of the North Atlantic region is poorly known, but apparently sites as far north as Ellesmere Island were warm enough during the Paleocene to support subtropical to warm temperate mammalian faunas.

For most of the Tertiary the middle American region remained isolated from South America. Changes in movements of several lithosphere plates created conditions appropriate for north-south island dispersal as early as the Miocene but a true land connection, the existing isthmus, did not form until the Pliocene. Paleontological evidence suggests that tropical conditions were not prevalent there until after that event.

A faunal list of 362 sub-fossil Coleoptera obtained from 33 published and 24 unpublished sites of Pleistocene age in Canada and the neighbouring United States is given. A table indicates the distribution of families, with the number of species encountered, through discrete intervals of Pleistocene time. Seven species representing members of the Carabidae, Hydrophilidae, Staphylinidae, and Scolytidae have been used to illustrate distribution changes through the last interglacial/glacial/present interglacial cycle. The maximum distance so far recorded is a shift of over 9000 km for Anotylus gibbulus (Epp.), a staphylinid, found fossil in Toronto during the last interglacial, and today recorded only from Eurasia and Asia. A number of other species whose modern ranges are confined to northwestern North America have been found fossil in the Great Lakes – St. Lawrence region, over 4000 km distant. A similar shift is noted in species which today are found only in the eastern Canadian Arctic. Aspects of ice build up, marginal conditions outside the Laurentide Ice Sheet limits, Pleistocene climates, paleoecology, and sub-fossil insect localities are used to formulate hypotheses about three refugia around the perimeter of the Late Wisconsinan ice.

Munroe (1956) summarized knowledge of the distribution patterns and history of the Canadian insect fauna; and a general synthesis beyond his conclusions is not yet possible. Results of studies on Nearctic Nebria taxa illustrate present distribution patterns and provide clues to the history of the montane fauna of western Canada. Nebria species and subspecies diversity is greatest in the Coast/Cascade Mountains just south of Canada and decreases northward. Major centers of endemism are located south of Canada, in the Coast/Cascade and southern Rocky Mountain systems, with minor centers found in western Alberta and the Queen Charlotte Islands. Species and subspecies vicariance patterns link Coast/Cascade and Rocky Mountain systems across the Okanagan lowland; and subspecies vicariance patterns link (1) Coast and Cascade mountains across Puget lowland/Georgia Strait and (2) central Canadian Rocky Mountains and Rocky Mountains of western Wyoming. These and other data presented on Nebria distribution patterns and faunal similarities among different mountain ranges and systems suggest that the present montane fauna of western Canada is derived from two source areas—one in the Coast/Cascade Mountain region, one in the Rocky Mountain region, each just south of the Canadian/U.S. border—which were separate and distinct during and after Wisconsinan time. Northern (e.g. Beringian) Wisconsinan refugia apparently did not contribute significantly to the present montane fauna.

The insect fauna of the Canadian prairies is composed of elements recruited from surrounding biomes. Most species appear to have invaded from the southeastern United States following the retreat of the last glaciation. Other distinct centers of origin are the eastern boreal forest, the Rocky Mountains, the Alaskan-Beringian refugium, and the Sonoran or interior basin of the southwestern United States. Because of the youthfulness and instability of the prairies as a biome, true prairie endemic species are rare. While an inventory of prairie insects is far from complete, enough information is available to detect basic patterns of immigration.

The distribution patterns of species of Coleoptera occurring in eastern Canada are examined. The following patterns are discussed: eastern ranges, northeastern ranges, amphiatlantic ranges, boreal ranges, subarctic ranges, arctic ranges, and introductions. The historical development of each of these ranges is discussed relative to their expansion from refugial areas.

Because little is known of the pre-settlement insect fauna of Canada it is now almost impossible to assess all of the changes that have been caused by settlement. For most of the time that has elapsed since colonization began, settlements have been small and scattered, and land use has been non-intensive. Many refuges for native insects persisted until very recently, and many still persist but are diminishing. Thus probably few aboriginal species have been driven to extinction. Many ruderal and cultivated plants accompanied settlers from Europe and Asia. Some of these provide an expanded food supply for a few native insects and these have expanded their numbers and ranges. Other native insects have been displaced and diminished by depletion of forests and planting of crops. Exotic plants are inevitably accompanied by exotic insects and Canada has provided a hospitable home for a multitude of exotic insects. Over 300 species have been deliberately introduced for biological control.

Once established in a colonial environment, the exotic origins of immigrant species are difficult to detect. Seven criteria for detecting exotic insect populations are suggested.

The impacts of settlement on the principal geographic regions of Canada and their probable influence on insect faunas are briefly discussed.

It is concluded that the insect fauna of Canada has been greatly enhanced by settlement.

Recent developments in ecological theory pertaining to the coexistence of insect species in response to forest disturbance are reviewed, and the findings are applied to the requirements for the Biological Survey of the Insects of Canada. It is important that a data collection system have a sound theoretical base, otherwise it will probably be found inadequate for the purpose for which it was designed. Questions about changes in faunal assemblages should be related to the scale of disturbance relative to the replacement time of the forest. Recommendations for research on faunal assemblage disturbance relationships are made for the Forest Insect and Disease Survey of Canada, and for the northern boreal forest.

Chironomid fossil assemblages in sediment cores collected from the Bay of Quinte, Lake Ontario, were examined to assess the impact of cultural development on the aquatic environment and to estimate, semi-quantitatively, the relative importance of the various impact processes influencing the chironomid communities. The impact of the six cultures defined in the core—the British–Modern, French, Iroquois, Algonkian, Hopewell, and pre-Hopewell periods—was exerted through eutrophication, sedimentation, and contamination processes. Although the chironomid communities in general followed the accepted theories of faunal response to eutrophication, the impact of sedimentation compounded and at times overshadowed the impact of eutrophication. The chironomid community, which responded to initial European colonization by developing a more eutrophic fauna parallel with increased productivity in the bay, reverted to a more oligotrophic fauna when large scale deforestation of the watershed introduced massive amounts of clay sediments into the bay. The resulting unstable bottom conditions and dilution and/or burial of food materials led to an imbalanced oligotrophic fauna characterized by Micropsectra. This fauna was maintained until the high rates of mineral sediment accumulation declined and the effects of eutrophication became manifest. The transition from the imbalanced oligotrophic fauna to the depleted Chironomus/Procladius fauna tolerant of the present-day eutrophic conditions was so rapid that the intervening mesotrophic Phaenopsectra community was unable to develop fully. The recent increased incidence of deformed larvae implicates industrial and/or agricultural contamination in the continued degradation of the Bay of Quinte fauna.

Primitive cultures similarly had measurable effects on the chironomid communities. The “more eutrophic” fauna engendered by the Hopewell culture was not inhibited by the accompanying accumulation of fine sediments as in the European periods and only reverted to a more oligotrophic fauna when reduced populations brought decreased productivity during the Algonkian and early Iroquois stages.