Canadian Journal of Arthropod Identification No. 42 (December, 2020) SHERIN Soldier flies of the subfamily Pachygastrinae of Canada (Diptera, Stratiomyidae) Linley M. Sherin McGill University, Department of Natural Resource Sciences, Macdonald Campus, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, H9X 3V9, Canada. Corresponding author: [email protected] Abstract The Pachygastrinae are a large, globally distributed subfamily of soldier flies (Diptera, Stratiomyidae). Despite being widespread, they have poor representation in museum collections and are mostly known from larvae collected under the bark of fallen logs. All seven Canadian genera and nine of the eleven Canadian species are herein reviewed and keyed. An updated checklist to the Canadian species is presented. Twenty-one new provincial records are reported, and four species are recorded from Canada for the first time: Cosmariomyia pallidipennis (Williston), Gowdeyana punctifera (Malloch), Neopachygaster vitrea Hull and Pachygaster pulchra Loew. This increases the known fauna in Canada from seven to 11 species. Published online December 04, 2020 Introduction Adults of the Nearctic Region are small (2.0– 3.6 mm), The Stratiomyidae, or soldier flies, are a large, predominantly black flies, often with silvery vestiture cosmopolitan family (~2850 spp.) of lower brachyceran (Kraft and Cook 1961; Woodley 2001). Though sexual flies that are diverse in both size and morphology (Hauser dimorphism is prevalent in soldier flies, Pachygastrinae et al. 2017; James 1981). There are 114 species recorded often display only subtle variation between sexes (Curran from Canada. However, a recent review of Canadian 1927). Adults of many species form swarms, and the Diptera predicted an additional 5-10 species remain to be Nearctic species Gowdeyana punctifera Malloch has recorded or described (Savage et al. 2019). The Canadian been recorded in swarms of up to 50 individuals (Woodley stratiomyid fauna includes species in seven of the twelve 2001). For unknown reasons, many species are collected subfamilies: Antissinae, Stratiomyinae, Beridinae, from windows (Hull 1930) and few were collected prior Sarginae, Nemotelinae, Clitellariinae and Pachygastrinae to the common use of Malaise traps (Woodley 2001). (McFadden 1972, Woodley 2001). I here review the Adults appear attracted to dead wood or fallen trees taxonomy of the 11 Canadian species of Pachygastrinae. where females oviposit (Woodley 2001). Pachygastrinae are a predominantly tropical subfamily Relatively little is known about the habitat with a global distribution. Possibly due in part to their associations and feeding habits of larval Pachygastrinae small size, they have poor representation in collections (Woodley 2001). Larvae are universally brown to white, when compared with larger stratiomyids. Pachygastrinae flattened dorso-ventrally and vary in length from 4.0 –7.2 are morphologically distinguished from other Canadian mm (Kraft and Cook 1961). Pachygastrine larvae are Stratiomyidae in having five visible abdominal tergites terrestrial and have been found under the bark and in tree (tergites 6 and 7 reduced), wing with m-cu crossvein holes of both deciduous and coniferous trees (Kraft and connected to vein M3+4, and in having only three veins Cook 1961; McFadden 1967). They appear to feed on arising from the discal medial cell (Fig. 1; James 1981; either the sap or microorganisms that occur on the moist Hauser et al. 2017). This subfamily was previously wood of wounded and dying trees (McFadden 1967) thought to be paraphyletic (Nagatomi and Iwata 1978; and use cylindrical brush-like mouthparts to sweep food Woodley 2001), however the only molecular study into their oral cavity (Cook 1953; Kraft and Cook 1961; of Stratiomyid phylogeny (Brammer and von Dohlen McFadden 1967). It has been suggested previously that 2007) found evidence of a monophyletic Pachygastrinae. the larvae are predatory (Malloch 1917; Johannsen 1922; Monophyly was also supported in a 2010 morphological James 1981). However, McFadden (1967) and Woodley analysis (Brammer and von Dohlen 2010), though (2001) considered it doubtful given their common pachygastrine representation was limited. appearance in large numbers with McFadden (1967) The Canadian Journal of Arthropod Identification is a product of the Biological Survey of Canada and the Entomological Society of Canada. doi:10.3752/cjai.2020.42 1 Canadian Journal of Arthropod Identification No. 42 (December, 2020) SHERIN Figure 1. Wing of Pachygaster pulchra Loew, edited to highlight characteristic wing venation of the subfamily Pachygastrinae in red; m-cu crossvein connected to M3+4, and only three veins arising from cell dm (M1, M2 apical and M4). Terminology follows Cumming and Wood (2017). Abbreviations: dm – discal medial cell; M – medial vein or media; M1+2 – fused first and second branch of medial vein;M1 – first branch of medial vein; M2 – second branch of medial vein; M3+4 – fused third and fourth branch of medial vein; M3 – third branch of medial vein; M4 – fourth branch of medial vein; m-cu – medial-cubital crossvein, m-m – medial crossvein. recording over 100 larvae existing under the bark of a Despite past attempts to generate a larval key to single log. The Canadian species Berkshiria albistylum species of Nearctic Pachygastrinae, no complete key Johnson has also been reared from a large number of currently exists. Kraft and Cook (1961) provided a larvae located under the bark of a fallen poplar tree larval key to genera and larval keys to species for three (Marshall, S.A., pers. comm.). genera (Eidalimus Kertesz, Gowdeyana Curran (as Previous work addressing the Canadian pachygastrine Eupachygaster Kertesz) and Zabrachia Coquillett). Most fauna has been limited and largely attributable to a small recently, McFadden (1967) provided a larval key to the number of dedicated dipterists. Kraft and Cook (1961) genera of Stratiomyidae in America north of Mexico and provided a revision of the Pachygastrinae of America incomplete larval keys to species. north of Mexico, including keys to 21 species, 13 of Current pachygastrine adult keys are also inadequately which were newly described in that paper. Following illustrated and none present an up-to-date review of the Kraft and Cook, James (1965) provided a supplementary Canadian fauna; the last Nearctic revision (Kraft and revision and key to the genera of the southwestern Cook 1961) included only five of the 11 Canadian species. United States and parts of Mexico, adding two species to I here key the seven Canadian genera including nine of the Nearctic fauna (one new species, Zabrachia yuccae the 11 Canadian species, illustrating adult diagnostic James, and one new Nearctic record, Cosmariomyia characters with photographs, adding new characters and pallidipennis (Williston)). James (1981) provided highlighting taxa that need formal revision. Four of the illustrated adult and larval keys to the subfamilies and species included here are new Canadian records (Table genera of Nearctic Stratiomyidae within the Manual of 1). By providing an updated and interactive key to the Nearctic Diptera, referencing 24 pachygastrine species Canadian fauna, I hope to encourage the future study of in its generic treatment. Most recently, Woodley (2001, the Pachygastrinae in Canada and bring attention to the 2011) provided a catalogue of the global Stratiomyidae. need for a global revision of the subfamily. I also hope This catalogue included 25 Nearctic pachygastrine that this key serves as a tool for amateur naturalists to species in nine genera, adding the species Artemita nana discover these beautiful and elusive flies. (Bellardi) to the Nearctic fauna. Of these 25 species, Woodley reported seven species from Canada (Berkshiria Materials and Methods albistylum Johnson, Eidalimus fuscus (Kraft & Cook), Species included in this key are those previously Neopachygaster maculicornis (Hine), N. occidentalis known from Canada (Woodley 2001) as well as new Kraft & Cook, N. reniformis Hull, Zabrachia plicata Canadian records reported from specimen data for the (Kraft & Cook) and Z. polita (Coquillett)) and another first time (Table 1). five species were recorded from the adjacent USA. Specimen data were obtained from the University doi:10.3752/cjai.2020.42 2 Canadian Journal of Arthropod Identification No. 42 (December, 2020) SHERIN of Guelph Insect Collection (DEBU, Guelph, Ontario), photograph. the Biodiversity Institute of Ontario (BOLD, Guelph, Ontario), the Canadian National Collection of Insects, Results Arachnids and Nematodes (CNC, Ottawa, Ontario), In total, 439 specimens were examined (52 DEBU, the Lyman Entomological Museum (LEMQ, Montréal, 20 BOLD, 262 CNC, 1 LEMQ, 101 QMOR, 2 UBCZ, Quebéc), the Ouellet-Robert Entomological Collection 1 iNaturalist) that correspond to nine species and seven (QMOR, Montréal, Quebéc), the Spencer Entomological genera (Table 1). Within this material, three specimens Collection (UBCZ, Vancouver, British Columbia) and were damaged and not identifiable to species. See the online platform iNaturalist [accessed 2020 October Appendix 1 for a complete list of examined specimens. 17]. Notably, no pachygastrine species have been recorded The following collections were also examined but held from provinces east of Quebec. This is potentially due to no Canadian Pachygastrinae: the Royal Ontario Museum sampling bias, as the most widespread species appear to (ROM, Toronto, Ontario), the Royal British Columbia exist wherever there are