"SHORT-HORNED" BUGS
(HOMOPTERA: AUCHENORRHYNCHA)
K.G.A. Hamilton
FAUNA OF ECOLOGICAL REGIONS
Out of 483 species of Homoptera-Auchenorrhyncha reported from the MCE, 129 are not analysed for geographical patterns, as they represent 25 imported (mainly European) species plus 104 wind-transported microleafhoppers. This leaves 354 species to be analysed. Of these, 174 (50%) are confined to valleys, 27 (6%) are confined to mountains and the rest are mostly widespread species of the boreal and hemiboreal zones. These numbers probably represent less than 90% of the actual fauna as there appears to be many species restricted to localized areas of the MCE. Even so, this is a large part of the entire fauna of these insects in Canada; together with the fauna of the Mixedwood Plains Ecozone fully 80% of Canadian “short-horned” bugs are represented in these two ecozones, of which only 132 species are in common to both zones.
Because sampling has not been uniform throughout the MCE some conclusions are only tentative. For example, a few mountains in the southern quarter of the Ecozone have been sampled on occasion, but no systematic collecting regime maintained throughout the growing season has ever been attempted.
The fauna of the MCE is a mosaic of very wide-ranging species and many localized ("endemic") ones. Well over 40% (154 of 353 analysed species) of "long-horned" bugs in the MCE are widespread, not confined to valleys or mountains. More than 70% of these widespread bugs (121 species) are leafhoppers; 10% (15 species) are delphacids and the balance represent only 1-5 species each of cicadas, treehoppers, spittlebugs, achilids and caliscelids.
Most of these widespread bugs, amounting to 110 species, apparently occur throughout the Ecozone. More than 85% of this fauna (94 species) have ranges that extend far beyond the boundaries of the MCE and the ranges of 81 species extend to the Atlantic Ocean. Sixteen species are western, widespread in the Cordilleran region of North America; they occur throughout the MCE. This fauna is composed almost exclusively of northern species that range into Idaho or at most the mountains of northern California, Utah and Colorado. The sole exception is a leafhopper, Colladonus flavocapitatus (Van Duzee), which is found throughout the west from Alaska to southern California (Nielson 1957). Most of the other species have ranges also extending far into the north. Four exceptions are notable: the spittlebug Aphrophora permutata Uhler and the leafhoppers Agalliopsis abietaria Oman, Cuerna cuesta Hamilton and Latalus curtus Beamer & Tuthill appear to reach their northern limits in the MCE and are probably restricted to valleys in the northern part of the Ecozone.
The other 44 widespread species occur only in part of the MCE. Twelve of them appear confined to northern latitudes and high elevations, being found in the Ecozone only in Ecoregions 198-207.
By contrast, 30 are found only in Ecoregions 205 and 208-212 in the southernmost third of the Ecozone.
Two other species are known from widely disjunct habitats in noncontiguous Ecoregions; their distributions cannot be explained at present.
What little data we have from remote and high elevation areas suggests a considerable uniformity of “short-horned” bug fauna in contrast to distinctive, localized faunas in the south. This overall uniformity at higher elevations and northern latitudes results in little correlation between the fauna of bugs (which seek out microhabitat conditions) and the distribution of Ecoregions (which are based on large-scale features and dominant conditions, which in turn largely represent montane conditions in the MCE). Only Ecoregions 208-212 and the southern half of Ecoregion 205 correlate well with bug distributions. This appears to be correlated in turn with a single ecological factor: over 1400 degree-days in the growing season.
By contrast, southern Ecodistricts often correlate well with bug distributions which represent valley faunas rather than montane faunas. Similarly, the ecological regions of North America (CCEA in prep.) split out the intermontane valley and ridge system of the southern MCE as a distinct ecological area common to the widespread Great Basin area in the U.S.A. The insects studied here are entirely in agreement with that opinion. They do, however, indicate that the boundaries are further south and at lower elevations than are currently drawn for the Great Basin (“Western Interior Basin and Ranges”) ecosystem.
VALLEYS AND MOUNTAINS
Very few mountains in the MCE have been sampled for “short-horned” bugs, and these are almost exclusively in the southern half of the Ecozone. The first summit of Mt. Harry (2500 m ASL) and Mt. Revelstoke (2000 m ASL), both E of Revelstoke in the Selkirks (Ecoregion 205), and Baldy Mountain (2000 m ASL) E of Penticton (Ecoregion 209) are the highest eminences from which leafhoppers have been recorded in MCE. The first two of these have a single endemic leafhopper Psammotettix beirnei Greene known from nowhere else in the world; its closest relative is restricted to Mt. Washington, NH (Greene 1971). Other bugs taken from mountains in the Selkirks and adjacent ranges (Ecoregions 205-207) are either endemic (Limotettix xanthus Hamilton) or the expected northern species that are usually the inhabitants of such cold, inhospitable regions: Idiocerus glacialis Hamilton and I. utahnus Ball & Parker, while in Wells Grey Provincial Park the eastern bog-inhabiting Limotettix humidus (Osborn) has been found. The fauna of more southerly mountains has only one such cold-adapted species: Macrosteles sordidipennis (Stål). Instead, a number of southern species otherwise known from few (if any) other localities in MCE have been found there, including the leafhopper Mesamia diana (Van Duzee) which is otherwise known only from the mountains of Mexico. The fact that a distinctive microleafhopper Empoasca nigra Gillette & Baker (an inhabitant of CO and UT) was found feeding on sagebrush only on the top of Mt. Kobau in the southern part of the Okanagan (Ecodistrict 1010) suggests that southern mountain faunas in MCE are enriched by wind-transported faunas of U.S.A. origin.
Collecting has been most thorough in valleys; thus discrimination of dispersal patterns is most reliable from these areas of the Ecozone. Dispersal patterns are also very apparent because the bug fauna there is highly fragmented. Only 12% (21 species out of 177) are widespread throughout valleys in Ecodistricts 978-991, 997, 1002-1015 and 1018.
Within the valley fauna there are definite patterns of distribution. The strongest distinction is between the valleys north and south of 51° N latitude, which appears to separate faunas of different ages. Northern districts (972, 978-9, 982) probably represent Hypsithermal relicts that are cut off from their parent populations in the Peace River district of the Great Plains by boreal forest. Southern populations, which are mainly of Great Basin origin, may be still invading from the south; for example, the range of the beet leafhopper Neoaliturus tenellus (Baker) varies greatly from year to year, indicating that it is wind-transported from the U.S.A. to British Columbia annually.
It is therefore not surprising that the southern valleys have by far the richer bug fauna: 92 species are endemic to small areas of southern valleys and another 44 species are widespread in southern valleys of Ecodistricts 991, 1002, 1005-12 and 1015. By contrast, in the north, 11 species are characteristic of valleys in Ecodistrict 982 and only 3 species are widespread in Ecodistricts 972, 978 and 982. Obviously, the Great Plains fauna is attenuated through the length of the Fraser valley.
A weaker east-west disjunction occurs between the Kootenay-upper Fraser and Okanagan-Kettle valley systems at 118° W longitude. This disjunction is most obvious in the fauna of specific valleys. For example, the semiarid grasslands of the East Kootenays resembles that of the southern Okanagan closely in dominant vegetation, but has less than 88% (65 of 74 species) of its valley-inhabiting leafhopper fauna in common, while the much larger Okanagan fauna has less than 50% (65 of 136 species) in common with the East Kootenays. This disjunction is also reflected in more widespread species distributions: 11 species are widespread in western Ecodistricts (978, 982, 1002, 1005-1011) while another 17 species are found only in the southwest (Ecodistricts 1002, 1005-1010) and 23 are characteristic of the Okanagan and lower Kettle Valley (Ecodistricts 1007, 1010, 1011) not counting the many species that are endemic to a single ecodistrict. The Kootenay-upper Fraser system (Ecodistricts 991-2, 1015) appears to derive at least part of its fauna of 8 distinctive species from the Great Plains via Montana; Ecodistrict 1015 has such prairie species as Amblysellus wyomus (Kramer) and Ceratagallia arida Oman that do not occur as far north as the Peace River district.
The valley-restricted species are mostly in the best-collected valley, the Okanagan (118 species or 65% of the valley fauna), divided roughly equally between the north Okanagan (Ecodistict 1007, 81 species) and the south Okanagan (Ecodistrict 1010, 74 species). Surprisingly, only 37 species are common to both ecodistricts. Ecodistrict 1010 has a distinctive semi-desert fauna feeding on such arid-adapted plants as sagebrush Artemisia tridentata Nutt., antelopebush Purshia tridentata (Pursh) DC and sand dropseed Sporobolus cryptandrus (Torr.) Gray. Ecodistrict 1007 has a grassland fauna adapted to somewhat moister conditions. The latter is enriched by the majority of introduced leafhoppers in the MCE, due to intensive agriculture supported by irrigation.
Other species-rich valleys are grouped around the arid Okanagan and Fraser valley systems.
Districts 982 (north Fraser valley), 1005-6 (Nicola and Thompson valleys) and 1015 (east Kootenay valley) are also species-rich faunas, with 44-39 endemic species. Districts 991, 1002, 1009 and 1011 are slightly less rich, with 29-22 such species; and minor faunas (10 or fewer endemic species) are found in districts 972, 978-9, 984, 990, 1001, 1003-4, 1008, 1012-3, 1016, 1018 although these are usually confined to just a small part (often a single short valley) within these ecodistricts.
Endemism is generally strongest in the most southerly ecodistricts such as the Similkameen valley (Ecodistrict 1009: 2 endemic species). Even plateaus there show endemism. For example, there are 6 endemics from Kamloops south to Douglas Lake (Ecodistricts 1005- 1006). The source for such endemism is unknown. Possibly increasing desertification of the Great Basin following retreat of the glaciers forced localized species northwards into Canada.
Of the southern ecodistricts, only #992 (around Moyie, B.C.) lacks any records of endemic species although collecting has turned up some widespread species there. This probably reflects the wetter conditions in its valleys than in adjacent valleys that are direct tributaries of the Great Basin ecosystem.
Other localized faunas, such as that of the upper Lillooet River valley (Ecodistrict 1002; 4 endemic species) and the adjacent lower Fraser valley (Ecodistricts 1002, 1005: 2 shared species) are extreme disjuncts that may be of Hypsithermal origin. The total range of such species suggests that Ecodistrict 1002 owes its fauna to the intermontane dry belt of Oregon and Washington states via the lower Fraser valley at a time when the British Columbia coast was much drier than at present.
