Species richness of gall midges (Diptera: Cecidomyiidae) in Europe (West Palaearctic): biogeography and coevolution with host plants.

The present fauna of the family Cecidomyiidae Macquart, 1838 in Europe includes 1800 valid species in 270 genera. It is divided into three subfamilies: Lestremiinae Rondani, 1840 with 280 species in 33 genera, Porricondylinae Enderlein, 1936 with 310 species in 62 genera and Cecidomyiinae Rondani, 1840 with 1210 species in 175 genera. Only the last subfamily includes gall-causing and plant-inhabiting species. For the family Cecidomyiidae, Europe is the most species-rich continent of the world. On average, each gall midge genus contains 6,6 species. The most species-rich genus is Dasineura Rondani, 1840, with 230 species, followed by Contarinia Rondani, 1860, with 135 species. On the basis of the larval feeding habits, the family Cecidomyiidae may be divided into three biological groups: 51% of species are phytophagous, 39% mycophagous, 8% zoophagous and the biology of about 2% remains unknown. All species of the subfamilies Lestremiinae and Porricondylinae are mycophagous. Fundamental sources for evaluation of the family Cecidomyiidae in Europe are 40,000 records about their occurrence and distribution gathered by the present authors at more than 1850 localities in 17 countries of mainland Europe and nine islands in the Mediterranean at altitudes from sea level up to 2645 m a. s. l. in the Alps in the period 1955–2009. All samples were obtained using the time and area unit collection method and results were enriched by data collected by earlier researchers. Evaluation was based on identified and valid species, not on unidentified and unnamed gall-inducing organisms. This abundant data enabled production of maps of occurrence of individual gall midge species of the Czech Republic, Slovakia, France, Spain, Portugal, Poland and Austria, and also graphs showing the vertical occurrences of some species in several countries of Europe. These were published in several summarizing articles (Skuhrava 1991, 1994a, b, Skuhrava & Skuhravý 2009a, Skuhrava et al. 2005, 2006). The accumulated data makes it possible to determine zoogeographical characteristics of single species occurring in Europe. Here we summarize information about the occurrence of gall midge species of the main genera in Europe and present results in maps of the following genera: Dasineura Rondani, 1840, Contarinia Rondani, 1860, Asphondylia Loew, 1850, Rhopalomyia Rubsaamen, 1892, Lasioptera Meigen, 1818, Stefaniola Kieffer, 1913, Rabdophaga Westwood, 1847, Jaapiella Rubsaamen, 1915, Resseliella Seitner, 1906, Macrolabis Kieffer, 1892, Baldratia Kieffer, 1897, and Mayetiola Kieffer, 1896. Evaluation of species richness using the average species number per locality showed that Hungary, with 29 species, France with 28 species and the Czech Republic with 26 species are the countries with the highest gall midge species richness in Europe. The average species number decreases to the north and to the south of Europe. Evaluation of species richness using the species density calculated for country or island unit area of 1000 km2 makes it possible to divide countries into five density groups. The Czech Republic and South Tyrol (northern Italy) are the countries with the highest species density, each with 189 gall midge species occurring per 1000 km2. Gall midges of Europe belong to the following zoogeographic or biogeographic units: 71% are European species, 12% Eurosiberian, 9.5% Mediterranean including Submediterranean, 1.3% Palaearctic or Euroasian, 4.5% Holarctic, 0.4% cosmopolitan and 1.3% are alien species. Gall midge species are not uniformly distributed in Europe. Many species were found only once at the type locality, some species are rare, others occur moderately frequently and only a few species occur very frequently. It is possible to divide all species found in the area under study into six frequency groups by using the first six members of the geometrical progression with quotient “2” and coefficient “a”, as follows: a.20 + a.21 + a.22 + a.23 + a.24 + a.25. The most frequent species in the whole of Europe is Jaapiella veronicae (Vallot, 1827) causing galls on Veronica chamaedrys; in northern Europe it is Iteomyia capreae (Winnertz, 1853) on Salix caprea; in southern Europe both Phyllodiplosis cocciferae (Tavares, 1901) and Dryomyia lichtensteinii (Low, 1878) causing galls on