Robert A. Cannings. 1998. Robber Flies (Insecta: Diptera: Asilidae) in Smith, I.M., and G.G.E. Scudder, eds. Assessment of species diversity in the Montane Cordillera Ecozone. Burlington: Ecological Monitoring and Assessment Network, 1998.
ROBBER FLIES
(INSECTA: DIPTERA: ASILIDAE)
Robert A. Cannings
ZOOGEOGRAPHY AND FAUNAL ELEMENTS
Faunal elements
Species may be grouped with others that share similar distributions to form what can be termed faunal elements. The majority of the 101 known species are confined to the Nearctic Realm, although two are Holarctic (defined here as species with transcontinental ranges in both North America and Eurasia). This section describes the Nearctic faunal elements pertaining to the fauna of the Montane Cordillera Ecozone (species with Holarctic and Palaearctic-East Beringian distributions are also assigned a North American faunal element). These faunal elements are:
1. Boreal (7 spp., 7%). Species occurring in the northern transcontinental forests dominated by spruce (Picea). In general, these species range from the Atlantic Provinces across the northern New England states, Quebec, northern Ontario, parts of the northern tier of mid-western states, the Prairie Provinces north of the Great Plains, and northern British Columbia, often ranging considerably southward in the mountains and plateaus of the Cordillera. Such species ranging south of the central plateaus of British Columbia (south of about 51oN) could be termed Boreomontane species. Laphria gilva (Linnaeus), Laphria insignis (Banks), Laphria janus McAtee, Laphria posticata (Say), Laphria sadales Walker, Cyrtopogon bimacula (Walker), Rhadiurgus variabilis (Zetterstedt).
2. Cordilleran (63 spp., 62%). Species confined to the western mountain systems and their associated plateaus. Largely confined to subalpine and montane coniferous forests. Cophura albosetosa Hine, Cophura vitripennis (Curran), Nicocles canadensis Curran, N. dives (Loew), N. pollinosus Wilcox, Laphria aimatus McAtee, L. asackeni Wilcox, L. astur Osten Sacken, L. asturina (Bromley), L. columbica Walker, L. felis (Osten Sacken), L. fernaldi (Back), L. ferox Williston, L. franciscana Bigot, L. milvina Bromley, L. partitor (Banks), L. sackeni (Banks), L. vivax Williston, L. vultur Osten Sacken, Pogonosoma ridingsi Cresson, Coleomyia hinei Wilcox & Martin, Coleomyia setigera (Cole), Callinicus pollenius (Cole), Cyrtopogon ablautoides Melander, C. albovarians Curran, C. auratus Cole, C. aurifex Osten Sacken, C. banksi Wilcox & Martin, C. dasyllis Williston, C. dasylloides Williston, C. fumipennis Wilcox & Martin, C. glarealis Melander, C. infuscatus Cole, C. inversus Curran, C. lineotarsus Curran, C. montanus Loew, C. nugator Osten Sacken, C. princeps Osten Sacken, C. sansoni Curran, C. sudator Osten Sacken, C. willistoni Curran, Dioctria pusio Osten Sacken, Eucyrtopogon calcaratus Curran, E. comantis Curran, E. diversipilosus Curran, E. nebulo Osten Sacken, E. punctipennis Melander, E. spinigera Curran, E. varipennis (Coquillett), Eudioctria sackeni (Williston), Heteropogon senilis (Bigot), Holopogon albipilosus Curran, H. stellatus Martin, Lasiopogon aldrichii Melander, L. cinereus Cole, L. monticola Melander, L. trivittatus Melander, Machimus callidus (Williston), M. occidentalis (Hine), M. vescus (Hine), Neoitamus brevicomus (Hine), Neomochtherus willistoni (Hine), Nevadasilus auriannulatus (Hine).
3. Intermontane (18 spp., 18%). Species of southern affinity in the western intermontane region, restricted to the valleys and lower elevation plateaus of the southern half of the ecozone. These are mostly grassland species, but this element may intergrade with the Cordilleran element in the open, dry montane forests of Ponderosa Pine and Douglas-fir at low and medium elevations. Some species may extend into adjacent areas of the Great Plains. Leptogaster fornicata Martin, Comantella pacifica Curran, Lestomyia sabulona (Osten Sacken), Nicocles utahensis Cordilleran, Dicolonus nigricentrum Adisoemarto, Dioctria henshawi Johnson, Myelaphus lobicornis (Osten Sacken), Scleropogon neglectus (Bromley), Stenopogon inquinatus Loew, S. rufibarbis Bromley, Willistonina bilineata (Williston), Stichopogon fragilis Back, Efferia benedicti (Bromley), E. coulei Wilcox, E. harveyi (Hine), E. n. sp., Megaphorus willistoni (Cole), Proctacanthus occidentalis Hine.
4. Western (6 spp., 6%). Species of western mountains and associated lowlands, but extending considerable distances eastward, often to the 100th meridian (Mississippi River). Leptogaster arida Cole, Cophura brevicornis (Williston), Ospriocerus aeacus (Wiedemann), Dicropaltum mesae (Tucker), Efferia frewingi Wilcox, E. staminea (Williston).
5. Transition (1 species, 1%). Species generally most common in the southern boreal forests and adjacent montane forests in the West and in the mixed and deciduous forests in the East. Laphria scorpio McAtee.
6. Austral (5 spp., 5%). Species ranging from coast to coast south of the boreal and mixed forests. Transcontinental at least in the United States; in Canada only in extreme southern areas. Laphria index McAtee, Andrenosoma fulvicaudum (Say), Efferia albibarbis (Macquart), Machimus erythocnemius (Hine), Proctacanthus milbertii Macquart.
7. East Beringian (1 spp., 1%). Species originating in the unglaciated areas of Yukon and Alaska and restricted to the eastern (North American) side of the Bering Strait. Lasiopogon prima Adisoemarto.
Zoogeographic Summary
The robber fly fauna of the Montane Cordillera Ecozone is overwhelmingly represented (81%) by species restricted to the western mountains, plateaus and valleys from the Rocky Mountains westward. These are the 81 species of the Cordilleran and Intermontane elements. The faunal elements are represented in the Montane Cordillera Ecozone as follows:
Sixty-three species of Cordilleran origin (62%) are recorded. Intermontane species total 18 species (18%) and there are 7 (7%) Boreal species, including two with holarctic ranges. Six species (6%) are Western, 1 (1%) is Transition, and 5 (5%) are Austral. One (1%) is Eastern Beringian.
Two species, Laphria gilva and Rhadiurgus variabilis, are holarctic, ranging around the Northern Hemisphere. Possibly, these species have had these wide distributions since before the last glacial age, living in the circumboreal forests that linked the continent. During the Pleistocene in North America, they could have lived south of the ice sheets. The Beringian glacial refugium has influenced the distribution of Montane Cordilleran asilids to only a small extent. The large and widespread holarctic genus Lasiopogon contains the only Beringian fauna in the Asilidae (Cannings 1997). Three species (L. hinei, L. canus and L. prima) are closely related to Eurasian forms; they or their ancestors entered North America through ice-free Beringia. L. prima is the sole species that reaches the Montane Cordillera, ranging south from the Yukon and northern British Columbia into the foothills of the Rocky Mountains in central Alberta. It is the eastern representative of a species pair that is separated by the Bering Strait. In the Yakutskaya, Magadanskaya, and Amurskaya regions of eastern Siberia and Far-eastern Russia its sister species L. septentrionalis Lehr is widespread.
Thirty-five percent of 20 Yukon species are of Boreal origin (Cannings and Cannings 1997); in the Montane Cordillera this boreal component is reduced to 7 percent. This reduction is the result of the overwhelming influence of more southerly species, because all of the Yukon's seven boreal species range south into the Montane Cordillera and only one additional boreal species (Laphria sadales) is included in the Ecozone's much larger total fauna (five times larger than that of the Yukon). All but one (Laphria posticata) of the seven species in the Boreal element of the Montane Cordillera range south of 51oN along the mountains and plateaus of the Cordillera. These also could be termed boreomontane species.
Robber flies apparently are seldom introduced to non-native habitats. Accidental introductions of larvae in soil would not be impossible, although densities are usually low. Purposeful introductions for biological control of insect pests would be impracticable because asilids are generalist predators and are difficult to rear. Nevertheless, two species have been introduced to eastern North America from Europe; the mode of introduction is unknown No non-native species live in the Montane Cordillera.
Robber Fly Habitat in The Montane Cordillera
The habitat requirements of most species of robber flies in the Montane Cordillera are known in only a most general way. Habitats are grouped here into three broad categories (Biogeoclimatic Zones in parentheses):
1. Subalpine forests and other spruce dominated forests: These spruce forests generally occur above 1200m in the south and 1000m in the north and on northern plateaus (Engelmann Spruce/Subalpine Fir, Montane Spruce, and Subboreal Spruce zones). In general, the dominant trees are Engelmann Spruce (Picea engelmanni) in the southern mountains and White Spruce (Picea glauca) in the north, with wide swaths of hybrids in the central regions. In many areas, especially in drier areas affected by fire, Lodgepole Pine (Pinus contorta) can dominate. Some asilids found in the meadows of these spruce forests may periodically appear above tree-line in the Arctic-Alpine Zone.
Typical robber flies are Laphria columbica, L. gilva, L. janus, L. milvina, L. posticata, L. sadales, Cyrtopogon bimacula, C. dasyllis, C. glarialis, Lasiopogon aldrichii, L. fumipennis (Cascade Mtns.) L. monticola, and Rhadiurgus variabilis. These are species of both the Boreal and Cordilleran elements. Some Cordilleran species living in subalpine habitats, such as those in the genus Lasiopogon, are restricted to the southern part of the Ecozone.
2. Montane forests. These are warmer forests growing below the spruces in the valleys and hillsides of the Montane Cordillera, mainly south of about Williams Lake. They are dominated by Ponderosa Pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) (Ponderosa Pine and Interior Douglas-fir zones). In wetter areas such as the Shuswap and Kootenay regions, Western Hemlock (Tsuga hetrophylla) and Western Redcedar (Thuja plicata) predominate (Interior Cedar-Hemlock Zone). Much of the understorey of the open dry forests is similar to that of adjacent grasslands and the robber fly species characteristic of forests and grasslands often intermingle.
The forest fauna is dominated by the large genera Laphria and Cyrtopogon, the larvae of which tunnel in rotting wood. Species characteristic of low and mid-altitude woodlands include Leptogaster arida, Cophura albosetosa, C. brevicornis, Nicocles dives, Andrenosoma fulvicaudum, Laphria aimatus, L. columbica, L. felis, L. fernaldi, L. ferox, L. franciscana, L. gilva, L. insignis, L. janus, L. sadales, L. vivax, Pogonosoma ridingsi, Coleomyia hinei, Callinicus pollenius, Cyrtopogon auratus, C. banksi, C. glarealis, C. inversus, C. montanus, Dioctria pusio, Eucyrtopogon calcaratus, E. nebulo, Eudioctria sackeni, Heteropogon senilis, Holopogon albopilosus, H. stellatus, Stenopogon inquinatus, Lasiopogon aldrichii, L. cinereus, L. monticola, Machimus callidus, M. erythocnemius, M. occidentalis, Neoitamus brevicomus, Neomochtherus willistoni, Nevadasilus auriannulatus.
3. Grasslands: The dry intermountain grasslands or steppes in the southern valleys and plateaus of the Montane Cordillera are dominated by various bunchgrass species and occur in three biogeoclimatic zones (Bunchgrass, Ponderosa Pine and Interior Douglas-fir zones). Lower elevation grasslands, below about 500 metres, are characterized by an arid community of plants dominated by Bluebunch Wheatgrass (Agropyron spicatum) and Big Sagebrush (Artemisia tridentata). In sandy soils Antelope-brush (Purshia tridentata) may replace sagebrush as a shrub, especially in the extreme south Okanagan. Middle grasslands on northfacing slopes in the main valleys and in areas such as the Nicola Valley generally lack sagebrush. Sandberg Bluegrass (Poa secunda) dominates with Bluebunch Wheatgrass and other species. The Upper Grasslands lie above about 800 or 1000 meters on hillsides and on the southern plateaus. Various species of fescues (Festuca) usually dominate the cover, although wheatgrass and needlegrasses (Stipa) are common and prevail in such regions as the Cariboo and Chilcotin plateaus.
Of the three habitat types, grasslands have the best known asilid fauna because the habitats are relatively restricted in size and are readily accessible to researchers. They are also frequently visited by collectors because their fauna has special and unusual species from the south. Some robber flies prefer specific grassland habitats relating to elevation, soil type and vegetation composition and structure; others are more widespread across different grassland types. Some species range into open Ponderosa Pine or Douglas-fir woods because much of the understory of such habitats is similar to that of adjacent grasslands.
Widespread species include Scleropogon neglectus, Stenopogon inquinatus, Efferia benedicti, Efferia harveyi, Proctacanthus milberti, Machimus occidentalis and Neomochtherus willistoni. Examples of others that occur in grasslands and adjacent open forests in the extreme southern part of the Ecozone but are rather rare are Leptogaster fornicata, Nicocles utahensis, Dicolonous nigricentrum, Ospriocerus aeacus, and Willistonina bilineata.
In low elevation, sandy, xeric habitats characteristic species are Stichopogon fragilis, Efferia albibarbis, and Proctacanthus occidentalis. In silty soil where Big Sagebrush flourishes, Efferia benedicti is common. If forbs are abundant, the rare Megaphorus willistoni may occur. Efferia staminea and an undescribed Efferia prefer Bluebunch Wheatgass in well-drained sites.
Middle and higher grasslands dominated by Festuca grasses support species such as Comantella pacifica, Lestomyia sabulona, and Myelaphus lobicornis (only where Common Rabbit-brush [Chrysothamnus nauseosus] grows) in the south. Species typical of the central plateaus tend to be widespread grassland species: Stenopogon inquinatus, Scleropogon neglectus, Dicropaltum mesae, Efferia coulei, E. harveyi and Machimus occidentalis.
