Midges of the genus Pseudodiamesa Goetghebuer (Diptera, Chironomidae): current knowledge and palaeoecological perspective

Abstract

Larvae of the genus Pseudodiamesa Goetghebuer, which includes 12 described valid species and is divided by Makarchenko and Makarchenko (1999) into two species groups, Pseudodiamesa branickii group and Pseudodiamesa nivosa group, are widespread in lakes and running waters of cold, high-latitude and high-altitude areas of the Northern Hemisphere. Larval remains of the genus are often found in subfossil assemblages from these cold regions, but intra-genus morphotypes usually are not distinguished by palaeoecologists. Current knowledge of the ecology of the species indicates that the Pseudodiamesa nivosa group is more cold-adapted than the Pseudodiamesa branickii group and, therefore, these two intra-genus morphotypes cannot be amalgamated into a larger taxonomic unit without losing substantial information. Here we present the morphological characters of head capsules of Pseudodiamesa larvae attributed to the different speciesgroup morphotypes, which are clearly visible in subfossil specimens. The information summarized in this paper will help provide more reliable chironomid-based palaeoclimatic inferences from lake sediment records covering colder phases through the late Quaternary in the Northern Hemisphere.

Whole Issue

“…With admittedly limited experience with Pseudodiamesa larvae from other parts of the world I have never come across what I would describe as lamelliform SI setae in Pseudodiamesa. What I have seen, however, is that the apically bifid SI claimed to be unique (Ilyashuk et al 2010) to the American endemic P. pertinax may also be observed in Norwegian larvae with labral lamellae ( Figure 1C). The specimen pictured here actually has a split on the right SI only.…”

“…If so, we should conclude that Schmid also has documented presence of P. arctica in the Alps, but then what should we do with P. nivosa? I find it intriguing that while Ilyashuk et al (2010) repeatedly state that P. arctica is the only species with labral lamellae, they also show a photo (Ilyashuk et al 2010: fig.1D) of what they call P. nivosa in which the specimen clearly seems to possess a labral lamella ( Figure 1B). Was this taxonomically important detail (as this paper testifies) overlooked by the authors or was it perhaps being interpreted as another type of structure?…”

“…If we use the pairs of distinctive chaetulae basales as landmarks to define the outer margins of the pecten ( Figures 1A, D), we see that there is symmetry around only one median tooth, the one which is numbered 4 in Figures 1 C-D. In other words, the assertion by Ilyashuk et al (2010) stating that all previous authors (including Oliver, Schmid, Janecek) were wrong when counting seven epipharynx scales in species other than those of the branickii -group does not seem justified. et al (2010) are also maintaining the notion that the labral lamellae are a unique feature of P. artica larvae.…”

“…In a more recent taxonomic review of Pseudodiamesa Ilyashuk et al (2010) refer to Makarchenko's (1985 fig. 1C).…”

“…The observation that Ilyashuk et al (2010) may have got the numbers of epipharynx teeth wrong in what they call nivosa unfortunately also leaves their claim that arctica has eight epipharynx teeth somewhat suspect. So are arctica and nivosa really separable as larvae?…”