Cerceris fumipennis Say (Hymenoptera: Crabronidae) is a solitary, ground-nesting wasp occurring east of the Rockies in the United States of America (Scullen Reference Scullen1965). Within Canada, it is widely distributed throughout southern Ontario, and colonies have also been found in western Québec (Buck Reference Buck2004; Marshall et al. Reference Marshall, Paiero and Buck2005; Careless et al. Reference Careless, Marshall, Gill, Appleton, Favrin and Kimoto2009; Careless Reference Careless2010). There is one historical record from Lytton, British Columbia (two females collected by R.H. Beamer on 3 August 1935; University of Kansas Natural History Museum, Lawrence, Kansas, United States of America), but since then no other specimens had been collected in western North America (except for one from Wyoming, United States of America locality, see below). Female wasps dig individual burrows up to 20 cm beneath the surface with cells originating from the central tunnel. Females provision each cell with paralysed buprestid beetles (Coleoptera: Buprestidae) upon which larval wasps will develop (Hook and Evans Reference Hook and Evans1991; Marshall et al. Reference Marshall, Paiero and Buck2005). As C. fumipennis provisions its nest with a wide variety of buprestid beetles, including several species of Agrilus Curtis, it has been used in Canada and the United States of America as a biosurveillance tool to detect the emerald ash borer, Agrilus planipennis Fairmaire, a non-indigenous beetle from Asia that is killing millions of ash (Fraxinus Linnaeus, Oleaceae) trees in eastern North America (Careless et al. Reference Careless, Marshall, Gill, Appleton, Favrin and Kimoto2009; Nalepa et al. Reference Nalepa, Teerling, Rutledge, Swink and Arellano2012; Careless et al. Reference Careless, Marshall and Gill2014). In the United States of America, citizen scientists are deployed to “adopt” and monitor C. fumipennis colonies for emerald ash borer and other non-indigenous buprestid beetles (Rutledge et al. Reference Rutledge, Fierke, Careless and Worthley2013). Cerceris fumipennis can easily be recognised even by non-experts (Careless Reference Careless2010) because of its distinctive colouration (dark, black or blackish brown stigma; ivory instead of yellow markings on head and body; only tergum 2 with a wide ivory band, bands reduced or absent on other terga), its morphology (female clypeus without prominent process), and relatively large size (6.0–13.5 mm, usually at least 8.5 mm).

The very differently coloured Cerceris californica Cresson is the western equivalent of C. fumipennis, preying upon buprestid beetles in British Columbia and the western United States of America (Scullen Reference Scullen1965). In 2012, various locations near Merritt, British Columbia were initially examined for C. californica nests with the intention of using it as a biosurveillance tool. A single female Cerceris was captured in a sweep net on 3 August 2012 to the west of the parking lot at Central Park, located at Vogt Street and Burgess Avenue (Fig. 1), and sent to M.B. The specimen was identified as C. fumipennis, but it differs slightly from eastern specimens (see below).

Fig. 1 Location of Cerceris fumipennis nests (red circle), Central Park, Merritt, British Columbia, Canada (50.11875°N, 120.78348°W).

On 7 July 2013 one male and three females were captured using a sweep net at the exact same location and determined by M.B. as C. fumipennis. A paralysed buprestid (possibly Chrysobothris species) lay next to the entrance hole of one of the nests (Fig. 2). The nesting area is essentially an extension of the parking lot and is exposed to full sun throughout the day. It is comprised of hard, compact, sandy soil with some sparsely distributed low lying vegetation. The nesting area occurs in an area with a lot of foot and vehicle traffic. However, unlike the parking lot, the nesting area does not have a top layer of gravel. Some moderately sized (10–35 cm diameter at breast height) trees (Acer Linnaeus, Sapindaceae; Fraxinus; Quercus Linnaeus, Fagaceae; and Sorbus Linnaeus, Rosaceae) as well as shrubs are planted as ornamentals at this park. Ponderosa pine (Pinus ponderosa Douglas ex Lawson and Lawson, Pinaceae) occurs naturally along the park’s border and throughout the city. Merritt (elevation: 595 m) occurs within the Bunchgrass biogeoclimatic zone, which is characterised by warm to hot, dry summers, and moderately cold winters (Anonymous 2014a). Merritt has an annual mean rainfall of 189.3 mm with an average maximum July temperature of 26.2 °C and an average minimum January temperature of −10.8 °C (Anonymous 2014b). The five specimens collected in 2012 and 2013 are deposited at the Royal Alberta Museum (Edmonton, Alberta, Canada).

Fig. 2 Chrysobothris species at nest entrance, Central Park, Merritt, British Columbia, Canada.

During the last week of July 2013, other potential nesting sites in the region were also searched, including baseball diamonds, campsites, dirt walking paths, school yards, and dirt running ovals in Cache Creek, Ashcroft, Spence’s Bridge, Skihist Provincial Park, Lytton, Boston Bar, West Kelowna, and Vernon. No other specimens were collected or observed flying.

The specimens from British Columbia (Figs. 3, 5, 7) differ from eastern (Figs. 4, 6, 8) C. fumipennis as follows: Except for the apparently smaller size (wing length ♀:9.5–10.5 mm [n=6], ♂:8.5 mm [n=1]; eastern C. fumipennis ♀:9.5–13.5 mm [n=75], ♂:6.0–11.5 mm [n=55], specimens examined from Canada: Ontario and United States of America: Delaware, Florida, Georgia, Kentucky, Maryland, Massachusetts, Minnesota, Nebraska, North Carolina, Pennsylvania, Texas, West Virginia; deposited at University of Guelph, Guelph, Ontario, Canada, and Royal Alberta Museum), the specimens from British Columbia differ from eastern populations only in colouration. Ivory markings of head more extensive (especially males), including mark on supraclypeal area and often scape or interantennal carina (all absent in eastern C. fumipennis, except for spot on scape which is present in 5% of males). The only male from British Columbia with large ivory clypeal spot (spot absent in 75% of eastern males, spot large in only 7% of males). Female with well-developed ivory spot on lateral portions of clypeus, small in one specimen (usually absent in eastern C. fumipennis, rarely with a small spot). Flagellum brown to yellowish brown beneath, especially in basal half (dark brown to black in eastern C. fumipennis, except for flagellar apex of male, which is usually pale). Ivory spots on pronotum small or absent (well developed in eastern C. fumipennis). Ivory fascia on tergum 2 narrow and broadly emarginate medially (wide and usually not emarginate in eastern C. fumipennis). Ivory markings on terga 3–5 of female more developed than in eastern C. fumipennis, including markings on tergum 3 that are as wide or almost as wide laterally as fascia on tergum 2, forming a complete or interrupted apical band (reduced to small lateral spots or absent in eastern C. fumipennis, laterally at most one third of width of fascia of tergum 2). Profemur often with posteroventral ivory stripe near apex, rarely also on mesofemur (absent in eastern C. fumipennis). Wings noticeably less infuscated than in eastern C. fumipennis, tinted faintly greyish-brown except for marginal cell, submarginal cells, distal part of radial cell, and areas distad of these on fore wing, which are more substantially infuscated.

Fig. 3 Female Cerceris fumipennis habitus (Merritt, British Columbia, Canada). Wings hardly infuscated except fore wing anteriorly. Ivory markings absent on pronotum, more developed on terga 3–5 (see diagnosis).

Fig. 4 Female Cerceris fumipennis habitus (Ontario, Canada). Wings strongly infuscated. Ivory markings present on pronotum, usually absent on terga 3–5 (see diagnosis).

Fig. 5 Female Cerceris fumipennis head (Merritt, British Columbia, Canada). Flagellum brown beneath, ivory markings more extensive (see diagnosis). This specimen with only minute ivory spots on scape, supraclypeal area and interantennal carina (these spots distinct in two other females but smaller than in male, see Fig. 7).

Fig. 6 Female Cerceris fumipennis head (Ontario, Canada). Flagellum black beneath, ivory markings more restricted.

Fig. 7 Male Cerceris fumipennis head (Merritt, British Columbia, Canada). Flagellum brown beneath, ivory markings more extensive (see diagnosis).

Fig. 8 Male Cerceris fumipennis head (Ontario, Canada). Flagellum black beneath, ivory markings restricted.

These differences amount to a clear geographic differentiation of the British Columbia population, which contrasts with the fairly uniform pattern of eastern C. fumipennis, despite the extensive latitudinal range of the latter (spanning from southern Canada to Florida and Texas). Undoubtedly, the geographic isolation of the British Columbia population has contributed to its distinctness, with the closest known eastern populations ~1000 km to the southeast (near Old Faithful, Yellowstone National Park, Wyoming, United States of America) and separated by high mountain ranges. The two Wyoming specimens (a male and a female, collected 13 July 1966, Florida State Collection of Arthropods, Gainesville, Florida, United States of America) indeed belong to the eastern colour form of C. fumipennis, as was confirmed to us by Kevin Williams (Florida State Collection of Arthropods; personal communication). In the absence of further data (structural characters or genetic evidence) we see no merit in assigning a new name to this geographic race, since geographic colour variation in widespread crabronid species is common place and such forms are not usually named.