Rocetelion fenestrale (Fisher)

Fitzgerald, Scott J., 2019, A Revision of the Holarctic Genus Rocetelion Matile (Diptera: Keroplatidae), Zootaxa 4648 (3), pp. 568-580 : 572-577

Rocetelion fenestrale (Fisher)

Figs. 2 , 5, 6 , 9, 10 .

Rocetelion fenestrale ( Fisher, 1938) , p. 197 as Ceroplatus fenestralis . HT male (ANSP); USA: Michigan .

Type material examined. HOLOTYPE male ( ANSP): USA: MICHIGAN: “ Isle Royale, Mich / Aug. 3–7, 1936 / C. Sabrosky ” [white label] / TYPE / Ceroplatus / fenestralis ♂ / E. G. Fisher 1938 ” [red label].

Additional material examined. CANADA: ONTARIO: Low Bush, Lake Abitibi , 16 Aug. 1925, N.K. Bigelow (1 female, CNCI) ; USA: ALASKA: Grande Denali Lodge , in window, 63.742740, -148.887810, 14 July 2016, S. Fitzgerald (1 male, SFC) .

Diagnosis. In the Nearctic region, males can be distinguished from the similar R. fasciola by the gonostylus apically rounded ( Figs. 5–6 ) and ventromedial membranous area of gonocoxites T-shaped ( Fig. 6 ) and females can be distinguished from R. fasciola by tergite 10 triangular, broad anteriorly, narrowing to a point posteromedially ( Fig. 9 ), and sternite 10 more tapered and not as apically broadly rounded as in R. fasciola (compare Figs. 10 and 8 ). Additionally, the known males of R. fenestrale have an unbanded abdomen ( Fig. 2 ) whereas it is banded in males of R. fasciola ( Fig. 1 ). See Diagnosis under R. humerale for distinguishing R. fenestrale from R. humerale .

Distribution (geographical and seasonal). This species is known from Ontario, Canada and Alaska and Michigan, USA. From the few specimens of this species that are known it appears to have a Nearctic boreal distribution. Specimens have been collected 14 July–16 August.

Remarks. Matile (1988) considered R. humerale to be the sister species of R. fenestrale . A side-by-side com- parison of these two very similar species leaves one questioning whether the subtle differences found between the Nearctic ( R. fenestrale ) and Palearctic ( R. humerale ) forms represent interspecific differences or intraspecific varia- tion of one Holarctic species. However, so few specimens of either species is available for study that, at present, this question can’t be further explored. The distribution of characters in the specimens examined in the present study agree with Matile’s (1988, 1990) illustrations and are consistent with Matile’s conclusion that R. fenestrale and R. humerale represent distinct, but very closely-related species. Therefore, despite the differences between the forms being small, in the absence of contradictory evidence R. fenestrale is retained as a distinct species.

The female of this species was previously unknown. Fisher (1938) mentions only the holotype male in the origi- nal description and Matile (1988) noted only a single male. The female tentatively treated herein as R. fenestrale was collected in Low Bush, Ontario and was not collected/associated with males. No additional specimens, male or female, were among the CNCI material collected in Ontario. However, the type locality on Isle Royale, Michigan is about seven miles from the Ontario border and about 400 miles from Low Bush. This female has an unbanded abdo- men which fits the general habitus of males of R. fenestrale (though some R. fasciola females can also be unbanded) and has terminalia that differ from the only other known Nearctic species ( R. fasciola ) which appears to be restricted to the West coast of North America.

Figures

FIGURE 1. R. fasciola, male, habitus (British Columbia, Canada). Scale bar = ca. 1.0 mm.

FIGURE 2. R. fenestrale, male, habitus (Alaska, USA). Scale bar = ca. 1.0 mm.

FIGURES 3–6. Male terminalia of R. fasciola (3,4) and R. fenestrale (5,6). 3, 5 – dorsal view, 4, 6 – ventral view. Scale bars = ca. 0.5 mm. Abbreviations: cer, cerci; ep, epiproct; gc, gonocoxite; gs, gonostylus; ma, membranous area; T9, tergite 9.

FIGURES 7–10. Female terminalia of R. fasciola (7,8) and R. fenestrale (9,10). 7, 9 – dorsal view, 8, 10 – ventral view. Scale bar = ca. 0.5 mm. Abbreviations: cer, cerci; S7, sternite 7; S8, sternite 8; S10, sternite 10; T7, tergite 7; T10, tergite 10.