A Contribution to the Knowledge of Holarctic Parachironomus Lenz (Diptera: Chironomidae), With Two New Species and a Provisional Key to Nearctic Adult Males

greater Los Angeles urban area (USA, California), adult males of the genus Parachironomus Lenz were encountered, which according to the North American reference literature represented the originally European species monochromus (van der Wulp, 1874). Simultaneously collected pupal exuviae, however, did not match the descriptions of monochromus, but appeared to be P. tenuicaudatus (Malloch, 1915). Certain transatlantic differences in monochromus male hypopygial morphology – first noticed by Goetghebuer (1951) – were also apparent. A wide array of material and references has been studied to resolve these inconsistencies and identify the southern Californian species, extending the original problem. The North American Parachironomus fauna clearly is not as well described as assumed, and a full review of Holarctic scope is required. As a first step, the present study attempts to resolve a limited set of outstanding problems, and identifies others. The species treated here are presently inseparable as larvae (3 of 4 known), and differ little to moderately in pupal and adult male morphologies (P. monochromus more noticeably in both stages). However, no shared autapomorphies or simple character sets have been identified distinguishing them from all their congeners. Thus, the selection of species for the present work perhaps does not form a monophyletic grouping, but is rather a result of the author’s interpretation of the available information. More associations of still undiscovered or poorly known Parachironomus immature stages, and the integration of data on all stages are required for an authoritative Holarctic revision.