Description of the female of Platycheirus altomontis Merlin & Nielsen in Nielsen, 2004 (Diptera, Syrphidae) with notes on the occurrence and hilltopping behaviour of rare French montane and Alpine Syrphidae

Abstract

A focused search in very high (2500–3200 m asl) Alpine mountain tops in France resulted in the discovery of the very rare Alpine-endemic syrphid Platycheirus altomontis Merlin & Nielsen in Nielsen, 2004, including its hitherto unknown female. A description of the female is given and further complemented with behavioural observations of this species with special reference to hilltopping. Additional records and behavioural observations are provided for rare and new species for the French fauna from the montane and Alpine habitat with focus on species of high altitude (>2750 m) and hilltopping behaviour. The species Rohdendorfia alpina Sack 1938 is new to France and was observed in large numbers at scree slopes above 2750 m and males were found sitting at hilltops up to 3200 m. Hilltopping behaviour of Syrphidae was observed over the whole altitudinal range visited, and multiple species engaged in this behaviour even at above 3000 m. Hilltopping appears to be more common in some genera (e.g. Parasyrphus and Pipizella) than in others and may be linked to specific phenotypes in some species. The latter was observed for the species Cheilosia melanura (Becker, 1894) of which at high hilltops much smaller males were found than at lower altitudes.