Contribution to the faunistic and ecological study of the blackflies (Diptera : Simuliidae) of Morocco - IV. The blackflies of the High Atlas mountain range. Description of a new species

Blackflies have been collected along the main river systems of the High Atl as range between 1985 and 1991. Immature instars of Simuliidae were importa nt members of the benthic fauna in these streams, Larvae and pupae were col lected from 54 sampling stations (between 450 and 3800 m a.s.l.) which incl uded a great diversity of running waters from trickles to rather large rive rs. The blackfly community consists of 24 species; six species are new to scien ce. Five species were previously described. A complete description of Simul ium (Eusimulium) mellah Giudicelli & Bouzidi sp. n. is given in the present paper. The number of blackfly species presently recorded from High Atlas is remark ably high in comparison to several European and Mediterranean countries; co nversely, a relative scarcity of species has been observed fur the other Fa unal groups inhabiting the High Atlas running waters. Many species are shared with the blackfly fauna of western Europe and most of Mediterranean Europe. The blackfly fauna of High Atlas clearly appears p alearctic, dominated by elements of west-mediterranean and circummediterran ean distribution; it also includes some african ones. Four species are ende mic: they live in high-altitude torrential streams and springs. Information on the biogeography, ecology and distribution of the species ar e given. Ecological affinities and relations between the 50 stations and 23 selected species have been determined by means of a Correspondance Analysis. Five c lusters of species and stations have been recognized : a first cluster char acterizes the cold-water torrential streams and spring brooks at the highes t altitudes (2660 to 3200 m a.s.l.); the 2nd and 3rd clusters correspond to the crenal and the initial sectors of the rhithral (between 1600 and 2700 m a.s.l.) and to a community of cold-stenothermous species; the 4th cluster is a community of eurythermic widely distributed species corresponding to mountain rivers (hypo-metarhithral) between 1200 and 2600 m a.s.l.; the 5th cluster includes the thermophilous and potamophilous species and their hab itat which is related to the lower course of the rivers (between 600 and 16 00 m a.s.l.). A factorial correspondances analysis was carried out on samples of inverteb rates, collected monthly from dec. 1985 to dec. 1986, in various microhabit ats (defined by current velocity and substratum) of two epipotamic river st retches. The first factorial axis (F1) represent a current velocity scale. The immature stages of 7 blackfly species are arranged on this axis in a de fined order in terms of their rheopreferendum.