The Bee Flies (Diptera: Bombyliidae) of Ontario, with a Key to the Species of Eastern Canada
Joel H. Kits* , Stephen A. Marshall* , and Neal L. Evenhuis**
* Department of Environmental Biology, University of Guelph, 50 Stone
** Department of Natural Sciences, Bishop Museum, 1525 Bernice Street,
It is astonishing that a diverse group of animals as attractive as the bee flies — fuzzy, colorful and conspicuous — should have been entirely neglected by a whole generation of Canadian entomologists, naturalists and ecologists. It is also unfortunate, for we have been almost completely ignorant of the many remarkable bombyliid species associated with habitats ranging from agro-ecosystems through to threatened dunes, grasslands and peatlands. The only possible reason for the dearth of bombyliid studies in Canada is the taxonomic impediment. Bee flies, like many arthropods, have been flying below the zoological radar screen because of the impression that they are difficult to identify. One of the main objectives of this paper is to correct that impression, or at least put it in the past tense.
We have given brief notes on the Ontario distribution in each species treatment; however, some species are especially significant because of their apparent rarity or habitat-restriction. Two species (Toxophora amphitea Walker and Poecilanthrax bicellata (Macquart)) are known only from one or two southern Ontario grasslands (Ojibway Prairie and Walpole Island), and another (Paravilla separata (Walker)) is known only from Walpole Island, Pinery Provincial Park and St. Joseph Island. Others (Dipalta banksi Johnson, Chrysanthrax dispar (Coquillett), Bombylius fraudulentus Johnson, and the Ontario species of Geron (Geron) Meigen and Tmemophlebia Evenhuis) are dune grassland associates; except for D. banksi, these are all known from very few sites. Villa fumicosta Painter is known from only two Ontario sites, both peatlands. Other very rarely collected species in Ontario without the apparent habitat restrictions of the dune, grassland and peatland species include Apolysis sigma (Coquillett), Anastoechus barbatus Osten Sacken, Bombylius atriceps Loew, Aldrichia ehrmanii Coquillett, Metacosmus mancipennis Coquillett, Anthrax argryopygus Wiedemann, Anthrax pauper (Loew), and Anthrax pluto Wiedemann.Some of these species may be more common than collecting records suggest. For example, Anthrax argyropygus and Anthrax pauper are both known in Ontario only from historical (1919) specimens labeled “Jordan, Ontario”. We have relatively few recent specimens from the Niagara region of Ontario so it is possible that this apparent rarity/disappearance is a collecting artifact. Anastoechus barbatus is known to occur both in western Canada and the James Bay region of Quebec, and probably occurs across boreal Ontario; the lack of records may be due in part to the limited collecting effort in that range. Both Apolysis sigma and Metacosmus mancipennis are small and easily mistaken for other families (Empididae and Pipunculidae, respectively), which may cause general collectors to bypass them. For the most part, the habitat and host requirements of these rarely collected species are unknown, and may in some cases be limiting factors in their abundance.
Most bee flies are ectoparasitoids, with active first instar triungulin larvae that attach themselves to hosts, usually insect larvae, in concealed places such as burrows or nests. Although hosts remain unknown for the majority of Canadian species, most of the species with known hosts are ectoparasitoids of solitary bees and wasps and are thus most likely to be encountered in the kinds of open, dry habitats that support the greatest diversity of aculeate Hymenoptera. Some of the bee flies found seeking hosts over open, sandy ground attack hosts other than bee and wasp larvae, including grasshopper egg pods (Anastoechus Osten Sacken, Systoechus Loew), tiger beetle larvae (some Anthrax Scopoli), or antlions (Dipalta Osten Sacken). Several groups, including Villa Lioy, Exoprosopa Macquart, Systropus Wiedemann and the Phthiriini, are parasitoids (usually endoparasitoids) of moth larvae and pupae. Some, such as Hemipenthes Loew, have been recorded as hyperparasitoids of other parasitoids that attack caterpillar and sawfly hosts (Hemipenthes species also attack the caterpillar and sawfly hosts). Host use in the Bombyliidae has been comprehensively reviewed, most recently by Yeates and Greathead (1997). Little work has been done specifically on host use in eastern Canada, although Packer (1988) found Bombylius pulchellus Loew to be a major cause of brood mortality in the halictid bee Halictus ligatus Say in Ontario.
Although bee flies are relatively well known taxonomically, there are some remaining taxonomic issues that need to be resolved. Problems in some genera include difficulties both in assigning the correct names to Ontario taxa and in evaluating the distinctiveness of closely related forms. Of the taxa occurring in Ontario, the most problematic is the genus Villa. This is the largest genus in Ontario, but the most comprehensive key dates to the 19th century (Coquillett 1892b). Little has been published on Villa since then, and a thorough revision is required. Recent revisions of the Nearctic fauna are also lacking for several related genera, including Hemipenthes, Chrysanthrax Osten Sacken, and Exoprosopa, although Ontario has only a few species in each of these genera. The subgenus Geron (Geron) was recently revised (Hall and Evenhuis 2003), but species of this subgenus remain difficult to identify since the key relies on dissection and it is necessary to compare genitalia to published figures or reference specimens.
The majority of species will be identifiable by reference to the species plates, but if in doubt it is best to begin with the dichotomous keys. There is considerable variation in some bee fly species: sexual dimorphism is frequent, and body size and colour often vary between specimens of the same species. Individuals occasionally show aberrant wing venation, sometimes with extra or missing crossveins. Hairs are easily rubbed off specimens; although many rubbed specimens can be identified by comparison with intact individuals, some can become impossible to identify when heavily denuded (particularly Villa species).
We thank J. M. Cumming and J. Skevington (CNCI, Ottawa), B. Hubley (ROME, Toronto), R. Roughley (JBWM, Winnipeg), and Nigel Wyatt (BMNH, London) for giving us access to specimens under their care. C. Lambkin and an anonymous reviewer provided many helpful comments that greatly improved the quality of this key. We also acknowledge Dave Cheung for help with graphics and all personnel in the University of Guelph Insect Systematics laboratory for providing much of the material used in this study. Danielle Fife and Nick Moore assisted with testing the keys.
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