Head

Width across eyes 2.83–4.05mm; width of frons below antennal bases 0.92–1.32mm; width of vertex (narrowest point between eyes) 0.78–0.88mm; height of facial gibbosity measured from eye margin 0.37–0.63mm. Tomentum white gold on face and along eye margins, thinning on occiput, on gibbosity, and at oral margins, revealing shining black cuticle. Mystax white, often mixed with pale-yellow bristles, especially ventrally; black/dark brown bristles concentrated above mouth, sometimes scattered throughout. Palpal setae dense, black/dark brown, sometimes mixed with golden ones, rarely all or mostly golden. Beard (genal setae) white, more or less pale yellow near eye margins. Orbital setae white, some black; ocellar bristles black. Occipital bristles golden, thickest medially, in some specimens mixed with black or white ones medially; surrounded by white hairs. Proboscis black with white and gold bristles.

Antennae

Lengths of antennal scape 0.36–0.48mm, pedicel 0.18–0.24 mm. Three flagellomeres: F1 elongate, tear-shaped, and laterally flattened, 0.40–0.53mm long, 0.12–0.18mm wide; F2+3 cylindrical, thin, 0.60–0.83 mm long, about 1.5–1.6 times longer than F1; F3 minute. Antennae brown, with thin pale tomentum on F1. Setae mostly white and ventral on scape, often some are black brown; shorter and fewer on pedicel, none on F1.

Fig. 14.

Fairview–White Lake Road, Oliver Mountain area, BC. View south from 49°11′16′′N, 119°35′10′′W (535m), 19 May 2010. Purshia tridentata/Pseudoroegneria spicata habitat; Pinus ponderosa stand in the middle distance. Photograph: Robert A. Cannings.

Thorax

Thorax cuticle brown black, largely covered with tomentum; subshining. Prothorax tomentum brown grey; hairs white, dorsal bristles golden. Scutum with gold brown tomentum mixed with grey, parts shifting to dark brown depending on angle of view. In dorsal view acrostichal stripes dark brown flanking grey medial line; tomentum lateral to dorsocentral setae golden; viewed from posterior, dorsocentral stripes dark brown. Short postpronotal setae mixed black and white. Acrostichal and dorsocentral bristles black, the latter longer, about 1.4 mm long posteriorly; presutural bristles 3–4, usually 3, either golden or black; postalar bristles black, 2–3, usually 3; supraalar setae black, 1–3, usually 2. Most of scutum sparsely covered with fine black hairs; usually white hairs anteriorly and along lateral margins. Scutellum tomentum gold brown with varying amounts of grey; apical scutellar bristles 7–14, black, often with golden tips; a few sometimes all golden; hairs on scutellar disc black, sometimes a few white. Pleural and scutellar tomentum grey mixed with gold brown. Katatergite bristles black; anepisternum hairs sparse, mostly white dorsally, black posteroventrally. Most of the other pleural sclerites bear long fine white hairs, often mixed with black ones.

Legs

Metafemur 3.8–5.2mm long. Base colour of leg segments dark brown–black; basal half of tibiae and tarsi often red brown, the amount of this colour on tibiae decreasing from pro- to meta-tibia. Coxae and trochanters mostly with gold brown to grey tomentum, white hairs and golden bristles, sometimes a few black ones. All leg segments mostly with white hairs and long fine setae, but femora often with black setulae and hairs; often some black hairs on tibiae and tarsi. Most leg spines black, a few golden. Dense golden brush of short setae on ventral face of apical half of protibia and at least first tarsal segment on pro- and meta-tibia.

Wings

Wing 9.8–13.5mm long; membrane hyaline, usually pale brown adjacent to veins. Veins pale to dark brown, usually red brown; short recumbent black setulae along anterior costa, sometimes as far at wing apex; normally some white setulae at costal base. Vein R4 and R5 branch opposite base of M2 (the distance between the r-m crossvein and the branching of R4 and R5 is about the same as the distance between the r-m crossvein and the base of M2). R4 with short recurrent vein near base, vein ending in cell r 2+3; infrequently the end of this short vein is connected to R4+5. Vein R₅ curved anteriorly, joining costa just anterior to wing apex. Halter pale brown, knob darker.

Abdomen

Tergite 1 mostly black-haired dorsally, a mix of black and white hairs laterally; usually 3–10 strong golden or black bristles laterally. Tergites 1–4 black dorsally, subshining, with lateral tomentum gold brown, paler apically, extending onto dorsal black areas in some lateral views, especially on basal or apical margins of segments; small basolateral patch of white tomentum on 4. Short hairs on dorsum black; lateral hairs long and spreading; mixed white and black on tergites 2–3, all white on 4. Tergites 5–7 with silver white tomentum, paler and more golden laterally on 5, hairs all white. Tergite 5 dorsally with golden tomentum bordering black basal and mid-dorsal areas; 7 dorsally with black apical band; 8 subshining brown with white hairs. Sternites 1 gold brown, 2–4 brown with gold posterior band, 5–7 mostly silver white; all hairs white. Sternite 8 with long stiff gold white setae apically.

Genitalia (Figs. 3–8)

Epandrium and gonocoxite black with white or pale golden hairs; fringe of gold white setae on venter of epandrium about 0.75 times as long as epandrium width. Dense fringe of setae on ventral margin of gonocoxite brown medially, white laterally, 0.5–0.8mm wide. Width of epandrium in lateral view about half the length (0.42–0.57 mm), widest at midlength; medial face of epandrium apex as in Figure 7. Hypandrium, gonocoxite, gonostylus, and phallus as in Figures 3–6. Details of Efferia genitalia were discussed by Theodor (Reference Theodor1976), Bullington and Lavigne (Reference Bullington and Lavigne1984), and Scarbrough and Perez-Gelabert (Reference Scarbrough and Perez-Gelabert2009).

Female (Fig. 2)

Body length: 12.0–19.2mm. Female coloration and setation much as in male, except on the abdomen and for a tendency towards sparser paler setae on most of the body. Major differences are noted below.

Head

Width across eyes 2.7–4.00mm; width of frons below antennal bases 0.90–1.33mm; width of vertex (narrowest point between eyes) 0.75–1.06mm; height of facial gibbosity measured from eye margin 0.37–0.73mm. Orbital setae white, rarely a few black; occipital bristles golden, in some specimens mixed with a few black ones medially. Antennae as in male.

Fig. 15.

Efferia okanagana sp. nov. Geographical distribution.

Thorax

Short postpronotal setae white, sometimes some black. Acrostichal and dorsocentral bristles black, usually mostly shorter and sparser than in male. Hairs on scutellum disc mixed white and black; when scarce, white ones usually concentrated basally. Katatergite bristles mostly gold or white, sometimes a few black, occasionally mostly black; other pleural setae almost always all white.

Legs

Metafemur 3.5–5.5mm long. All leg segments usually with white hairs and long fine setae; short black recumbent setae rarely on dorsal surface of femora; otherwise as in male.

Wings

Wing 9.0–13.8mm long; otherwise as in male.

Abdomen

Complex tomentum pattern changes with direction and angle of view. In posterodorsal view, segments 1–6 mostly dark brown basally, silver gold apically, the latter band covering about 0.3 times length of tergite 1, 0.25 times length of 2 (which also has a narrow basal band), 0.3 times length of 3, 0.5 times length of 4 and 5, 0.25 times length of 6, and none of 7. Intersegmental membranes have similar silver gold tomentum. Often a brown midline occurs. In anterodorsal view, tergites become mostly gold brown with pale-grey apical bands on at least tergites 2–4. In lateral view. tergites are silver grey ventrally, grey gold basally, and brown apically and ventral to the golden basal patches. Dorsal setulae and hairs mostly recumbent and white mixed with some black, black ones predominating along midline of tergites. Lateral hairs longer, white; tergite 1 mostly white-haired dorsally, with some recumbent black setae apically; white hairs and 5–6 strong golden or black bristles laterally. Tomentum of sternites mottled grey and brown; hairs long and white.

Genitalia (Figs. 9–12)

Ovipositor (mostly segment 8) laterally flattened, shining black, 3.8–5.0mm long (usually about 4.5mm long), about as long as segments 5–7; width at base 0.80–1.04mm, length about 5 times (4.0–5.5) basal width (Fig. 9). Tergite 9+cercus 0.60–0.92mm long; cercus length about half length of tergite 9 (Fig. 9). Genital fork, (sternite 9, furca), spermathecae, and associated structures as in Figures 11 and 12. Spermathecae extending anteriorly to middle or apex of segment 7. Terminal reservoirs of spermathecae ovate; external surface of duct bearing caniculi (Fig. 11).

Immature stages

The larva and pupa are unknown.

Habitat

All seven species of Efferia known in BC live in the Pacific Northwest Bunchgrass (Tisdale Reference Tisdale, Nicholson, McLean and Baker1982) type of intermontane grasslands of the region. The character and composition of these grasslands vary considerably with soil, altitude, and aspect. Efferia okanagana is an inhabitant primarily of the Lower Grasslands, which are dominated by bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) Á. Löve) (Poaceae) (Fig. 13) and big sagebrush (Artemisia tridentata Nutt.) (Asteraceae) (Nicholson Reference Nicholson, Nicholson, McLean and Baker1982; Tisdale Reference Tisdale, Nicholson, McLean and Baker1982).

However, most of the known localities for E. okanagana are in the southern Okanagan Valley south of Penticton on sandy and gravelly soils, where the Lower Grasslands are represented by a shrub steppe dominated by antelope bitterbrush (Purshia tridentata (Pursh) DC) (Rosaceae) (Fig. 14) rather than by A. tridentata, with needle and thread (Hesperostipa comata (Trin. and Rupr.) Barkworth (Poaceae)) usually common in the herb layer. Antelope bitterbrush plant communities mainly occur in the low-elevation valley bottoms (280–760m) in xeric sites of the driest variant of the Bunchgrass Biogeoclimatic Zone, BGxh1 (Very Hot Dry Bunchgrass). Some antelope bitterbrush plant communities also occur at the margins of the Ponderosa Pine Biogeoclimatic zone, PPxh1subzone (Very Hot Dry Ponderosa Pine). Artemisia tridentata is typically predominant in sites that have a capping of very fine sands and silts; these are considered a different ecosystem (K. Iverson, unpublished data).

The low-elevation grassland on the east side of Vaseux Lake is an example of the P. tridentata – H. comata community. One site where E. okanagana occurs has a scattered shrub layer dominated by P. tridentata with Rhus glabra L. (Anacardiaceae), Philadelphus lewisii Pursh (Hydrangaceae), and Amelanchier alnifolia Nutt. (Rosaceae). The herb layer is predominantly P. spicata and Aristida purpurea Nutt. (Poaceae) with lesser amounts of Erigeron glabellus Nutt. (Asteraceae), Selaginella wallacei Hieron. (Selaginellaceae), Panicum scribnerianum Nash (Poaceae), and Agoseris glauca (Pursh) Raf. (Poaceae). There is a considerable amount of weedy species such as Bromus tectorum L. (Poaceae), Vulpia octoflora (Walt.) Rydb. (Poaceae), and species of Centaurea L. (Asteraceae). The bryophyte and lichen layer is absent. Species present here but absent from the Penticton stand, in addition to those listed above, include Gaillardia aristata Pursh (Asteraceae), Astragalus purshii Dougl. (Fabaceae), and Crepis atrabarba Heller (Asteraceae).

In this region, E. okanagana is absent from many grasslands with finer soils where Pseudoroegneria (Nevski) Á. Löve and A. tridentata predominate. Extensive grasslands around White Lake, Chopaka, and Richter Pass, the Okanagan Lake benches from Penticton to Kelowna, grasslands north of Kelowna, and the sage-dominated silts in the lower South Thompson Valley west of Kamloops to Ashcroft and Cache Creek have not produced any specimens. These habitats are the home of Efferia benedicti Bromley from June to August and E. harveyi Hine from August to October. Interestingly, there are also no records of E. okanagana from the sandy P. tridentata steppe on the east side of Osoyoos Lake, despite considerable fly collecting there over many years. The typical species there is E. albibarbis (Macquart). The grasslands of the Rocky Mountain Trench (upper Kootenay and Columbia River valleys), dominated by P. spicata and species of Festuca L. with P. tridentata steppe in many southern sites, support E. frewingi Wilcox, which in Canada, at the northern edge of its range, is mostly a western Great Plains species.

Records of E. okanagana at the northern boundary of its distribution near Kamloops and Vernon come from Pseudoroegneria habitat; P. tridentata is not found that far north. In sites at Cosens Bay, Kalamalka Lake Provincial Park, Pseudoroegneria is predominant; other grasses include Stipa nelsonii Scribn., Koeleria macrantha (Ledeb.) Schult., Poa canbyi (Scribn.) Howell, and B. tectorum (all Poaceae). Forbs such as Balsamorhiza sagitatta (Pursh) Nutt. (Asteraceae) and the invasive Potentilla recta L. (Rosaceae) are common (Fig. 13). Artemisia tridentata is rare or absent in the sites where E. okanagana has been found.

In contrast, E. coulei (the other E. arida group species in the region) is much more widespread, occurring as far north as the Chilcotin Plateau (about 52°N, 123°W, 200km northwest of Kamloops). This species also is a spring flier, but prefers Middle Grasslands sites (characterized by grasses such as Festuca campestris Rydb.), which are generally more extensive in BC than are the Lower Grasslands and occupy somewhat cooler, moister situations (Nicholson Reference Nicholson, Nicholson, McLean and Baker1982; Tisdale Reference Tisdale, Nicholson, McLean and Baker1982). On the West Bench, Penticton, where E. coulei is common and the only Efferia species in spring, the herb layer is dominated by F. campestris and a low coverage of rabbitbrush, Chrysothamnus nauseosus (Pall.) Britt. (Asteraceae). Secondary species are V. octoflora, B. tectorum, Sporobolus cryptandrus (Torr.) Gray (Poaceae), and Phlox longifolia Nutt. (Polemoniaceae) There is a well-developed bryophyte and lichen layer consisting primarily of species of Cladonia P. Browne (Cladoniaceae), Peltigera Willd. (Peltigeraceae), and Pohlia Hedwig (Mniaceae). Plant species found there but absent from the Vaseux Lake site where E. okanagana is found include Lewisia rediviva Pursh (Portulacaceae), Fritillaria pudica (Pursh) Spreng. (Liliaceae), Ranunculus glaberrimus Hook. (Ranunculaceae), and Geum triflorum Pursh (Rosaceae).

Efferia larvae live in the soil (Lavigne and Holland Reference Lavigne and Holland1969) and a comparison of the general soil characteristics of sites inhabited by E. okanagana and E. coulei (which partition Okanagan grasslands in the spring) is warranted. Soil consistency may be a factor in the presence or absence of E. okanagana. The Vaseux Lake site (E. okanagana) is an alluvial terrace at the foot of metamorphic cliffs; the subsoil is a stony, gravelly alluvium. The surface soil is coarser and with a higher percentage of organics and salts and a lower moisture-holding capability than the soil in the Penticton site (E. coulei), which is deep and medium-textured. A relatively high percentage (more than about 10%) of gravel in the soils characterizes other sites where E. okanagana occurs, such as the east bench of Vaseux Lake (sandy loam, 45% gravel) and Kalamalka Lake Provincial Park (sandy to heavy loam, 8%–17% gravel). The species is absent from sites where gravels are less common, such as West Bench, Penticton (loam to fine sandy loam, 0%–1%), Chopaka (heavy sandy loam and clay, 5%), and Haynes Lease, Osoyoos (loamy sand, 3%) (R.A. Cannings, unpublished data).

Phenology

Thirty-five collection events recording flying adults range from 17 April (1930), Vernon) to 18 June (1991), Vernon, Kalamalka Lake Provincial Park). Thirty-one records are from May and two-thirds of all records fall between 15 and 25 May. The mean and mode of the May records are both 19 May. Seventeen photographs of adults at Oliver were taken by Werner Eigelsreiter (personal communication) between 24 April (2001) and 30 May (2007) (median 16 May).

Efferia okanagana has an early flight period relative to most other sympatric species of Efferia in southern BC grasslands. It flies at about the same time as E. coulei, its E. arida group relative. These two spring species are replaced in about mid-June by E. benedicti and E. staminea (Williston) (E. staminea group) and E. albibarbis (Macquart) (E. albibarbis group), which are the typical summer Efferia species in the region. Two E. pogonias group species fly later in BC: E. harveyi, the only true autumn species, flies from August until late October and E. frewingi Wilcox, a Great Plains species at the northern edge of its range in BC, flies mostly in August. Efferia frewingi is known in BC only from the Rocky Mountain Trench and is the only BC Efferia species that is broadly allopatric with E. okanagana.

In grasslands, ground-hunting robber fly species are most easily collected along trails or dirt tracks. These provide the flies with clear views of potential flying prey and maximum exposure to the sun. Most collections of adult E. okanagana have been made in such situations; when disturbed, they fly from the ground with a strong buzzing of wings, landing a few metres away, and are usually readily located. Where there are no trails, adult E. okanagana are most easily seen when they sit on rocks or pieces of wood. On sunny, warm days they are active from at least 10:00 a.m. to 18:00 p.m.

Oviposition

The ovipositor of E. okanagana is strongly flattened laterally. Efferia species with this type of ovipositor lay their eggs in or on vegetation; those with more cylindrical ovipositors lay eggs directly in the soil (Dennis et al. Reference Dennis, Lavigne and Bullington1986). On 23 May 1987, at Kalamalka Lake Provincial Park, Vernon, females laid eggs in the empty glumes of the previous year's P. spicata florets. As far as is known, E. okanagana has never been collected at a site where this grass is absent.

Prey

Only one specimen of E. okanagana has been captured with prey: a male with a winged ant (Formica sp.) was collected at Vaseux Lake on 17 May 1987. However, at Oliver, BC, Werner Eigelsreiter has photographed adult E. okanagana preying upon insects in five orders: Coleoptera (a click beetle (Elateridae)), Hemiptera (Errhomus calvus Oman (Cicadellidae)), Hymenoptera (species of Andrena F. (Andrenidae) and Hoplitis Klug (Megachilidae)), Lepidoptera (a species of Lampronia Stephens, probably L. aenescens (Walsingham) (Prodoxidae)), and Diptera (Syrphus opinator Osten Sacken (Syrphidae), Machimus Loew (Asilidae), and a species of Tipula L. (Tipulidae)). As well, he photographed a female E. okanagana feeding upon another female.

Distribution (Fig. 15)

Efferia okanagana is known only from Canada, but the range probably includes at least parts of adjacent Washington State where similar habitat occurs. In Canada the species is recorded only from BC in the Oliver, Vaseux Lake, Okanagan Falls, Vernon, and Kamloops areas in the Okanagan and Thompson valleys. Despite much collecting effort, few specimens have been collected. However, it may be more common than records suggest. It is patchily distributed within its area of occurrence and is apparently largely restricted to grasslands dominated by P. spicata and where the soils contain considerable gravel. This habitat occurs mostly at low elevations (280–760m) in the region (K. Iverson, unpublished data) but is much more widespread than the known distribution of the fly. See also the discussion in the Habitat section.

Conservation

The grasslands that support E. okanagana are limited in area and biologically diverse, and have been, and continue to be, degraded. They have received intense attention from conservation programs. For example, the P. tridentata – H. comata ecosystem in the southern Okanagan valley, where most of the E. okanagana sites occur, is assigned the highest priority (S1 Provincial status) under the provincial Conservation Framework goal, and G2 Global status. The ecosystem supports one of the highest densities of species-at-risk of ecosystems in BC (Dyer and Lea Reference Dyer, Lea and Seaton2003; K. Iverson, unpublished data).

Despite some successful attempts to conserve BC grasslands, many areas have been eliminated or reduced in size and condition because of development for agriculture, housing, recreation, and industry; changing fire regimes; disturbance by livestock; and the introduction and spread of invasive plants (Dyer and Lea Reference Dyer, Lea and Seaton2003; Cannings Reference Cannings2006; Lea Reference Lea2008; K. Iverson, unpublished data). In BC in 2010 only about 7.1% of the P. tridentata – H. comata ecosystem remained in good to excellent condition and 71.3% was in only fair condition (K. Iverson, unpublished data). Between 1800 and 2008, 67.5% of the original area (9863ha) was lost (3217ha remains), 40.7% of the losses occurring after 1938 (K. Iverson, unpublished data). As of 2010, about 17.4% of the remaining area of the ecosystem was protected; 56.2% was on First Nations Reserves, 20.0% was in private hands, and 6.4% was on unprotected provincial land.

Despite these adverse trends for the most important habitat of E. okanagana, nothing is known about the vulnerability of the fly. Although egg-laying may occur in grasses other than P. spicata, invasive weeds such as Centaurea diffusa Lam., B. tectorum, and P. recta may negatively affect oviposition by reducing Pseudoroegneria growth,. Overgrazing may be a concern for the same reason, although specimens of this and other species of Efferia in BC appear to tolerate considerable habitat disturbance.

Wildfires within the area of occurrence of E. okanagana increased in frequency from 2000 to 2010 and severely damaged some of this species— habitat (e.g., at Vaseux Lake and the nearby Ecological Reserve 100 at the north end of Osoyoos Lake). These fires tended to burn much hotter than previous fires and, in addition to destroying aboveground oviposition and foraging habitat, may have killed Efferia larvae and pupae in the soil. However, the Vaseux Lake population documented from specimens collected in the 1980s survived a severe fire in 2003.

Efferia okanagana is a rare asilid under significant pressure within its small known geographical area of occurrence. Its large size, predatory nature, and conspicuous behaviour make it an excellent subject for nature interpretation. These traits make it a good candidate for conservation planning and further inventory work. A status report on the species is currently in preparation (Committee on the Status of Endangered Wildlife in Canada, unpublished data).