Caddisflies of the Yukon - Department of Biological Sciences ...

838 G.B. Wiggins and C.R. Parker
margins on the inferior appendages. Eurasian specimens examined are, however, about
evenly divided between these 2 conditions. In the parameres of the male genitalia of Nearctic
Beringian specimens there are more than 10 long, very fine, setae on the dorsal preapical
lobe and the setae on the mesal surface extend anterad of the dorsal process. In specimens
from other parts of North America there are fewer than 10 setae on the dorsal lobe of the
parameres and the setae are coarser, as they are also in Eurasian specimens examined; but
the fine setae on the mesal surface in Eurasian material extend anterad of the dorsal lobe as
in Beringian specimens.
In females, the dorsal margin of segment IX is truncate in 98 per cent of Nearctic
Beringian specimens examined and also in Eurasian specimens, differing from the rounded
condition found in 87 per cent of North American populations generally. Segment X in dorsal
aspect is bifid in only about 17% of Nearctic Beringian females examined, but in 90% of
specimens from elsewhere in North America; in most Nearctic Beringian specimens the apex
of X is blunt or pointed rather than bifid.
This species is univoltine at Tuktoyaktuk, Northwest Territories, where larvae live in
tundra ponds (Winchester 1984).
Onocosmoecus unicolor (Banks) (122)
It seems likely that Onocosmoecus is part of a complex of dicosmoecine genera that
arose in North America (Wiggins and Flint in prep.). Marked variation in this species is
confirmed by no fewer than 6 synonyms, but analysis of specimens from many localities
revealed no congruent geographic pattern (Wiggins and Richardson 1987). We infer that
some populations passed the Pleistocene glaciation south of the ice in North America because
the only other species known in the genus, O. sequoiae Wiggins and Richardson, is confined
to the Sierra Nevada Mountains of California and may have originated there as a glacial
disjunct. Widespread occurrence of variable populations of O. unicolor in North America
from British Columbia to Newfoundland indicates that other populations of this species
extended across a broad front to the south of the glaciers, and that O. unicolor occurred in
North America before Pleistocene glaciation began. This leads to the further possibility that
other populations of O. unicolor in the Beringian refugium dispersed to eastern Asia across
the Bering land bridge during the Pleistocene glaciation. Larvae of this species live in cool
waters of slow streams and the littoral zone of lakes, habitats that would have been readily
available on the Bering land bridge; larvae in streams in interior Alaska fed entirely on plant
detritus (Irons 1988).
Molannidae
Molanna flavicornis Banks (127)
This is the only North American species of Molanna with a transcontinental distribution.
It is very similar to and is perhaps identical with the Eurasian Molanna albicans Zett.,
resulting in a circumboreal range through northern Eurasia and North America (Fuller 1987).
The albicans group of several species evidently arose in Eurasia and only this single Nearctic
extension now exists. Montane populations in Colorado are interpreted as glacial relicts,
indicating that this species ranged widely to the south of North American glaciers during the
Pleistocene, and thus its Holarctic distribution would have been established before Asia and
North America were separated in the Pliocene. Larvae live on the bottom of cool lakes.
Molannodes tinctus Zetterstedt (128)
Collections of this northern Eurasian species in Alaska and the Yukon have led to the
entrenched view that it was a glacial relict confined to the Beringian refugium. In recent