What’s in a name? A previously unrecognized species of North American black fly from Baffin Island

Biting flies are a scourge at northern latitudes. Nearly every early explorer made reference to the tenacity and voracity of these tiny insects. Not surprisingly, biting flies reach their peak abundances in northern environments, with mosquito densities reaching a staggering 12.5 million individuals per hectare in the Hudson Bay Lowlands. Similarly, black fly larvae can reach densities of 1.2 million per square meter of stream substrate under optimal conditions. Given their abundances, and economic importance (through blood feeding and transmission of parasitic diseases), it is not surprising that biting flies are among the best known insects in North America.

Black flies are an especially well known as they were the subject of a monumental revision of the North American simuliid fauna by Adler et al. (2004).  In fact, no new North American species have been described since that book was published 9 years ago. Consequently, I was amazed to discover a hitherto unknown species near Iqaluit, NU on southern Baffin Island (Figure 1). It is a member of the circumpolar genus Stegopterna (Enderlein 1930) which includes 8 North American species.  However, only one species — St. emergens (Stone 1952) — is known to be distributed widely at northern latitudes.

This previously unknown species was overlooked during initial sorting and counting. However, subsequent DNA barcoding, revealed >10% sequence divergence between this species and Stegopterna emergens, the species it was initially mistaken for. This prompted a closer examination of the morphology of the Iqaluit population, which differed from St. emergens in 2 important ways. The first relates to the length of the pupal gill trunk (Figure 2). Pupal gills are often used for species level identification of black flies, and this difference was consistent in all specimens examined. However, a more striking and ecologically significant difference is that the Iqaluit species has mouthparts adapted for blood feeding. Distributional records reveal that, of the 9 black fly species previously recorded from the Canadian Arctic Archipelago, only 2 had biting mouthparts. The other species were arctic-adapted (i.e., non-bloodsucking) species that use nutrients from their larval stages to develop their eggs. Interestingly, the two biting species were both found only on southernmost Baffin Island.

The discovery of this previously unknown species of bloodsucking black fly raises important ecological and evolutionary questions. Historical records suggest that St. emergens was present on southern Baffin Island during the 1950s; however, contemporary collections yielded only this previously unrecognized one. Were historically collected specimens simply mistaken for this undescribed species, or was St. emergens supplanted by this new one on southern Baffin Island? Reexamination of historically collected material in the Canadian National Collection of Insects is needed to select from these alternative hypotheses. DNA barcoding may again prove useful should the diagnostic life stages (i.e., adult females, pupae) prove unavailable for study.

Another important question is why southern Baffin Island was the only region in the Canadian Arctic Archipelago to historically support bloodsucking black flies. The recent discovery of yet another blood feeding species on the Island (Schaefer 2011) further reinforces the suitability of conditions for this feeding habit. A more favorable climatic regime seems a likely explanation; however, further analyses are required.

Finally, this undescribed species was not present at any other Arctic or Boreal site sampled by the NBP. This raises the question of how widely distributed this species is. There have been no records of morphological or chromosomal differences between mainland and continental island populations, nor have any continental island endemic black flies have ever been found in North America. This makes it extremely unlikely that this new species is restricted to Baffin Island and suggests its distribution likely extends southward into northern Quebec or westward across Nunavut (albeit in potentially low numbers).

The process of assigning a name to this previously unrecognized species is not particularly straightforward. While it’s possible that the southern Baffin Island Stegopterna is an undescribed (i.e., is a new to science) species, we can’t rule out the possibility that it’s actually a Holarctic species that already carries a valid scientific name.  Unfortunately, Stegopterna species are notoriously difficult to identify morphologically, and there are at least 7 candidate names to consider from the northern Palearctic Region (all members of the St. trigonium species complex). We must now begin the process of poring over species descriptions to determine whether any of the available names could reasonably be applied to the southern Baffin Island population. But however this exercise turns out, it’s gratifying to know that there are still new and exciting discoveries to be made in northern Canada.

References

Adler, P.H., D.C. Currie and D.M. Wood. 2004. The Black Flies (Simuliidae) of North America. Cornell University Press. Ithaca, NY.

Schaefer, P. 2011. Update on the biting fly component (Diptera: Simuliidae, Culicidae and Tabanidae) of the Northern Biodiversity Program. Newsletter of the Biological Society of Canada 30: 41-49.

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