Buil. Annh Soc. r. belge Ent. 133 (1997): 419-438 Dolicliopodid communities (Biptera: DoUchopodidae) in "De Kempen" (eastern Belgium): biodiversity, faunistics and ecology* by Dirk MAES1 & Marc POLLET2 1 Institute of Nature Conservation, Kliniekstraat 25, B-1070 Brussels, Belgium. Email: dirk. maes@instnat. be 2 Department of Entomology, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, B-1000 Brussels, Belgium. Email: [email protected] Summary During a large scale inventory in "De Kempen" (eastern Belgium), 12 sites were sampled for dolichopodids by means of Malaise traps and/or pitfall and water traps or by sweepnet between 1991 and 1995. A total of 7,865 specimens of 73 named species were collected, 22 of which were known from < 20 UTM 10 km-squares in Belgium. Dolichopus apicalis is recorded for the first time in Belgium and Medetera lorea for the second time. Ecologically, several communities could be distinguished: species from humid wooded habitats, the eurytopic Chrysotus gramineus, eurytopic species from eastern Belgium and species from open and sunny habitats. All abundant species seemed to be univoltine and activity peaks are reach• ed between May and July. Females were mostly collected in larger number than males and populations of Dolichopus ungulatus and Chrysotus grami• neus showed different activity patterns in adjacent habitats. Finally, the suitability of the Malaise trap in site quality assessment studies is dis• cussed. Key words: Diptera, Dolichopodidae, faunistics, ecology, biodiversity, De Kempen. Samenvatting Tijdens een grootschalige inventarisatie in De Kempen (Oost-België) werden tussen 1991 en 1995 12 plaatsen bemonsterd op slankpootvliegen Received: 5.II.1997. 420 Bull. Annls Soc. r. belge Ent. 133, 1997 (Dolichopodidae) door middel van Malaisevallen, bodem- en watervallen of met een sleepnet. In totaal werden 7.865 exemplaren van 73 benoemde soorten verzameld, waarvan 22 soorten bekend zijn van 20 of minder UTM 10 km-hokken in België. Dolichopus apicalis werd voor het eerst waarge• nomen in België en Medetera lorea voor de tweede maal. Verscheidene ecologische gemeenschappen konden worden onderscheiden: soorten van vochtige en bosrijke habitats, de eurytope soort Chrysotus gramineus, eu- rytope soorten uit het oosten van België en soorten van open en zonnige habitats. Alle abundante soorten lijken slechts één generatie per jaar te hebben met activiteitspieken tussen mei en juli. Wijffes waren meestal tal• rijker dan mannetjes en populaties van Dolichopus ungulatus en Chrysotus gramineus toonden verschillende activiteitspatronen in verschillende habi• tats. Tot slot wordt de geschiktheid van Malaisevallen voor het bepalen van de kwaliteit van gebieden besproken. Introduction The region of "De Kempen" (provinces of Antwerp and Limburg) is probably one of the most interesting faunistic areas in Belgium. Its dipte- ran fauna, however, is poorly investigated. MAES & DECLEER (1993) show• ed that a large number of interesting dipteran species occur in one particu• lar Nature Reserve studied in the region, but these authors did not deal with dolichopodid flies. Only POLLET et al. (1988) and POLLET (1991) re• ported the results of recent inventories, and faunistic and ecological data on dolichopodid flies collected during recent inventories in "De Kempen". To obtain more information on their distribution and ecology in this region different sampling techniques were used (Malaise traps and/or white water traps, hand catches or net sweeping) at different sites between 1991 and 1995. The main purpose of the present contribution is to present the entire species list with a discussion of the species of special faunistic interest, the ecology of the most abundant species and the dolichopodid biodiversity in the investigated region. Study area, material and methods Study area and sampling sites The predominantly sandy "De Kempen" is situated in the northern part of the provinces of Antwerp and Limburg (Belgium). Wet and dry heath- land types, inland dunes, peatmoors and fens are readily encountered in this region but are quite rare elsewhere in our country. Figure 1 shows the location of "De Kempen" in Belgium with the sampled nature reserves (NR) and other sampling sites indicated. The site codes used in Table 1 and Fig. 1 correspond with the following localities: Site A: "De Rammelaars" NR (Oostham, Limburg, UTM: FS46) is a small Nature Reserve (26 ha) with moist grasslands and deciduous wood- Bull. Annls Soc. r. belge Ent. 133, 1997 421 land (among which aldercarr). Dolichopodid flies were collected in diffe• rent habitats by hand and sweepnet on 11.VU. 1992 and 13.VII. 1992. Site B: "De Liereman" NR (Oud-Turnhout, Antwerpen, UTM: FS38) (168 ha) consists of different habitats: Erica and Calluna heathland, fens, peatmoor, aldercarrs and other deciduous and coniferous woodland types. Dolichopodid flies were collected by means of a Malaise trap at the border of a fen between 9. VI. 1992 and 4. VII. 1992. Site C: "De Vallei van de Grote Beek" NR (Leopoldsburg, Limburg, UTM: FS56) has a narrow and elongated shape (59 ha) and comprises meadows, dry heathland and coniferous and deciduous woodland (among which aldercarr). In these habitats dolichopodid flies were collected by hand and sweepnet between 9.VII. 1992 and 12.VII. 1992 and pitfall trap• ping (3 traps per habitat) from 28.11.1994 until 12.111.1995 in four diffe• rent habitats: a dry heathland, a mixed forest, a moist hayfield and an abandoned railway track. B K Fig. 1. Location of "De Kempen" in Belgium and of the sampling sites within this region. A, "De Rammelaars" NR (Oostham); B, "De Liereman" NR (Oud-Turnhout); C, "De Vallei van de Grote Beek" NR (Leopoldsburg); D-G, "De Vallei van de Zwarte Beek" NR (Beringen); H-I, "De Maten" NR (Genk); J, "Het Wik" NR (Genk); K, "Paepen- daaP (Zutendaal); L, "De Mieren" (Opoeteren). 422 Bull. Annls Soc. r. belge Ent. 133, 1997 Sites D, E, F and G: "De Vallei van de Zwarte Beek" NR (Beringen, Limburg, UTM: FS66) is one of the largest Nature Reserves in Belgium (ca. 1,000 ha) and includes a wide range of habitats: inland dunes, Callu• na and Erica heathland with fens, peatmoors, coniferous and deciduous woodlands and dry grasslands and meadows. Three sites were sampled by means of Malaise traps: site D ("De Katershoeve") is a dry extensively grazed pasture bordered by Calluna and Erica heathland at one side and mixed woodland at the other side. Malaise trap sampling was carried out between 6.V. 1992 and 10.X.1992. Site E ("De Kluut") is a clearing (with Molinia caerulea, Lysimachia vulgaris, Salix spec, and Rubus spec.) within a deciduous woodland area. Site F ("OCMW") is a humid oligotrophic grassland (with Equisetum fluviatile, Comarum palustre, Carex spec, and Lychnis flos-cuculi) within a woodland area and is mown once a year. In sites E and F a Malaise trap was in operation between 5.V. 1992 and 10.X. 1992. Prior to the former sampling campaigns, white water traps had been used in a variety of habitats ("site G") between 6.VII. 1991 and 21.VIII. 1991. Sites H and I: "De Maten" NR (Genk, Limburg, UTM: FS74) (204 ha) comprises Calluna and Erica heathland as well as large oligotrophic ponds and shallow fens. One Malaise trap (site H) was put in Erica heathland (with Molinia caerulea and Myrica gale) and another (site I) on the banks of a pond (with Myrica gale, Rubus spec, and Frangula alnus) between 1.V.1993 and 30.IX.1993. Site J: "Het Wik" NR (Genk, Limburg, UTM: FS74) is a small Nature Reserve (86 ha) with many ponds in a woodland area. One Malaise trap was in operation on the bank of an overgrown pond between 1.III. 1992 and 3.X. 1992. The dominant vegetation consisted of Salix spec., Myrica gale, Molinia caerulea, Frangula alnus and Pinus sylvestris. Site K: a private garden ("Paependaal") (Zutendaal, Limburg, UTM: FS74) with a pond in a deciduous woodland area. Flies were sampled with 1 Malaise trap from 1.V.1993 to 30.X.1993. Site L: "De Mieren" (Opoeteren, Limburg, UTM: FS86) is a derelict meadow of ± 40a (with Urtica dioica, Salix spec., Heracleum sphondy- lium and Typha latifolia) with a central pond. One Malaise trap sampled between 8.V. 1992 and 30.VII. 1992. Sampling and identification The collecting jars of the Malaise traps were for 1/2 filled with a 10% formaline solution and were emptied at more or less weekly (varying from four to ten days) or fortnightly intervals. Pitfall traps were emptied at fortnightly intervals. Dolichopodid flies were sorted out in the laboratory and identified by means of PARENT (1938), NEGROBOV & STACKELBERG (1972, 1974a, 1974b, 1977), D'ASSIS FONSECA (1978), POLLET (1990), MEUFFELS & GROOTAERT Bull. Annls Soc. r. belge Ent. 133, 1997 423 (1990) and some unpublished keys by Drs H. MEUFFELS (The Netherlands). Nomenclature is according to MEUFFELS et ci. (1991). The specimens are preserved in part in the collections of the Department of Entomology (Royal Belgian Institute of Natural Sciences, Brussels) and in the private collections of the authors. Data analyses In order to investigate the dolichopodid community structures in the sampled sites, multivariate analysis techniques were applied: Detrended Correspondance Analysis (DCA in CANOCO program, TER BRAAK, 1987) and Two-Way Indicator Species Analysis (TWINSPAN, HILL, 1979). In DCA, theoretical variables are constructed that best explain the variation in the species data. The first variable explains most of the variation, which is reflected by its highest eigenvalue. A second and further theoretical variables can be extracted from the data matrix but are subject to the cons• traint of being uncorrelated with the previous DCA variables. A further step in this analysis is the ordination of the species and site scores in an ordination diagram where the theoretical variables are represented by axes (Fig. 2).