,, BULLETIN bE L'INSTITUT ROYAL DES SC IENCES NATURELLES DE BELG IQUE ENTOMOLOG IE, 75: 305-3 I9 , 2005, BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN ENTOMOLOGIE, 75: 305-3 I9 , 2005 Succession of dance fly fauna (Diptera: Empidoidea: Empididae, Hybotidae, Microphoridae) in ancient forests and afforested former agricultural land: a case-study in the "Voerstreek" (Belgium, Flanders): faunistics and new species for the Belgian fauna by Patrick GROOTAERT, Wouter DEKONINCK & Konjev DESENDER Abstract Why dance flies ? I I2 species of Empididae sensu latu were found in forests at the In contrast to ' rare or uncommon' animal groups that are extreme eastern border of Flanders in a region known as the Voer­ streek. Seven species are recorded for the first time in Flanders. Two frequently used in site quality assessments, dance flies or species are also new records for the Belgian fa una: Rhamphomyia empidid flies are common and widespread. Too often, (Pararhamphomyia) murina Collin and Rhamphomyia (Rhampho­ only mammals, birds or butterflies are used in site quality myia) mg entata von Roder. Distribution of Red Data Book species is commented. assessment and they are not always representative for Four species supposed to be Extinct were observed; one species the area. On the contrary, dance flies are always present, Critically endangered was recorded: Rhamphomyia (Pararhampho­ even in small plots. During an annual cycle, up to 50 myia) marginata (Fabricius); four species are Endangered (3 .6%); four species can be observed in a particular biotope (station) species are Vulnerable (3 .6%); 35 species are Susceptible (31 %), one Near threatened and seven are Data Deficient (6%). 49 species are (GROOTAERT et al., 1988). Many species have a very tight Safe/low risk (43 %). Only 43 % of the species are safe and under low microhabitat preference and hence they are good indica­ ri sks, so even when th e Data Deficient species are not taken into tors for a specific habitat or enviromnental conditions. Of account, still 5 1% of the species are more or less threatened. Young forests of at least 20 years old show a higher species diversity course, most species are very common and belong to the than th e old or very young forests. However, if we consider the true Red Data Book status (RDB): Safe/Low risk. But some­ forest species, the reference forests (ancient) have more true forest times up to 30% of a species assembly are rare or threa­ species and the younger forests have less forest species. Forest planta­ tions and spontaneous afforestations that are more than 20 years old, tened. The combination of total diversity, i.e. the total start to have a dance fl y fau na resembling that of the old reference number of species, the munber of specific species for a forests. Forests yo unger than 15 years old contain onl y genera li st forest particular habitat or microhabitat (target species) and the species. The plantation of 1989 in Altenbroek approaches strongly the fau na of the reference forest. Colonisation of the plantation proceeds amount of individuals of a species combined with the more rapidly than in a spontaneous afforestation. rarity factor (Red Data Book status) allows to make site quality assessments (POLLET & GROOTAERT, 1999). Key words: Diptera Empididae, succession, ancient forests, afforesta­ tion, fa uni stics Niche of the dance flies The larvae of all empidids, as far as known, are carnivo­ Introduction rous and are living in the soil or in decaying wood (xylobionts). A very important limiting factor for the In order to compare the differences in natural quality of occurrence of larvae in the soil is the water saturation. spontaneous afforestation with artificial plantation of Apart from a few exceptions of species living in wells or new forest, a study was set up in the Voeren region in streams, the larvae are not adapted to living in an aquatic the extreme east of Flanders (Belgium). The fauna of environment. The adult flies are either obligate carnivo­ forest of various age, various origin and with a different rous or nectar feeders. The predators catch their prey grazing were compared to two ancient forests, the Alten­ either on a solid substrate (soil, surface of leaves or broek and Alserbos. These reference forests are known to vetiical walls), floating on a water surface or in flight. be there unaltered since more than 225 years and are so­ However, many species feed on nectar and hence might called Ferraris-forest since they are represented on the play an important role in pollination. Finally, there are Ferraris-maps. species that have a combined feeding strategy. They are Since the "Voerstreek" is situated in the extreme east nectar feeders, but the male captmes a prey to present to · of Flanders, it has a Central European fauna in contrast to the female during mating. In early spring, flower visitors the mainly Atlantic faun a of Flanders. This explains the belonging to the genera Empis and Rhamphomyia are huge number of new or rare species that were found especially abundant. Probably, they play an important during this study. role in pollination. From June on, it are above all pre- II 306 Patrick GROOTAERT, Wouter DEKONINCK & Konjev DESENDER dators that are abundant and dominant. They are vora­ Material and methods cious and probably play a role in the population regula­ tion of plant parasitic Diptera (leafminers and gall­ The Voeren region has the oldest sites in Flanders where midges). Dance flies constitute a food source for many afforestation was planned and canied out on fonner insectivorous animals such as spiders and birds. agricultural land on loamy soils. In the neighbourhood The occurrence of dance flies is above all determined of two forest relics (the Altenbroek and the Alserbos), by the stmcture of the habitat and landscape. In some relatively large areas have been designated for sponta­ surveys we showed that Empididae need different habi­ neous afforestation or to be altered to forest by plantation tats to complete their Iifecycle (DELETTRE et a!., 1992; of indigenous trees (VERSTRAETEN et a!. 2001; DEKO­ 1998) e.g. the larvae of Hilara live in a particular soil NJNCK et a!., 2005). At present, these two forests consist type, the male collects prey on water surfaces while the of many small plots with different age, structure and female swarms in areas with a particular stmcture. Em­ history and are as such are ideal to evaluate ctment on­ pididae also show a preference for habitats nonexposed going afforestation. to the sun, i.e. shaded locations with a high relative Dance flies were sampled in five sites of the Alten­ humidity. Consequently, forests are an evironment that broek forest and six sites of the Alserbos forest. The host many species. sampling stations situated on Fig. 1. Characteristics of all 1 I sampling stations are given in Table 1, whereas Systematics of dance flies details on soil and vegetation characteristics can be found in DEKON INC K et a!. (2005). In each station (VOERO I­ Approximately 272 species occur in Flanders (360 in VOER05 and VOER07-VOER12) 3 pitfalls (PT), 3 white Belgium). They are grouped in the superfamily of the water traps (WT) and one Malaise trap (MT) were in­ · Empidoidea (C!-IVALA, 1975) comprising the families stalled. All pitfalls (glass jam jars, diameter of 9.5 em) Empididae, Hybotidae, Microphoridae, Atelestidae and and white water traps ( 17x 10 em and 5 em high) were Dolichopodidae. In the present study, we envisage the installed in a row, spaced 3-5m apart. A 3.5% fonnalde­ fonner family of the Empididae sensu lata that groups the hyde solution was used for killing and fixation and some four families of the Empididae, Hybotidae, Microphori­ detergent was added to lower surface tension. Each Ma­ dae and Atelestidae (not found during this study). The laise trap collecting-vial was filled with a 75% alcohol Dolichopodidae or long-legged flies are dealt with in solution. All traps were emptied 12 times from 02-IV- another paper. A Red Data Book of the dance flies in 2003 until 08-X-2003. Flanders is available (GROOTAERT eta!. , 2001). Fig. I - Sampling stations in " Voeren" region. I' Afforestation: Case study "Voeren": Empidoidea 307 Table I - Code, history, description and age of the sampling sites. Site code Forest History Description of the site Forested since VOEROI Altenbroek Ancient forest Ancient oak-birch forest < 1775 de FeiTaris VOER02 Altenbroek Arable field Afforestation and low density grazing (Galloways), Salix sp. and 1996 birch. VOER03 Altenbroek Grassland Afforestation and low density grazing (Galloways), no shrubs or 1996 trees VOER04 Altenbroek Arable field Afforestation and intensive summer grazing, Salix sp. and birch 1996 VOER05 Altenbroek Arable field Plantation of Quercus robur 1989 VOER07 Alserbos Ancient forest Ancient oak-birch forest < 1775 de Ferraris VOER08 Alserbos Grassland Afforestation of birch 1980 VOER09 Alserbos Arable field Afforestation of birch 1980 VOERJO Alserbos Grassland Plantation of Prunus avium with fragments of spontaneous Callu- 1985-1990 na vulgaris VOERII Alserbos Arable field Afforestation of birch 1980 VOER12 Alserbos Grassland Plantation of Quercus robur 1985-1990 Results faunistics they can get at most the Red Data Book status of "Sus­ ceptible" or " Data deficient" since no records before the General results faunistics pivot year of 1980 are available. The trend criterion or percentage of decrease of the number of records after 9.639 individuals belonging to 112 species were collected pivot date of 1980 is the first criterion for the Red Data and identified (Table 2). Most specimens were caught Book. Their habitat not being threatened is a second with the Malaise traps (5.397), followed by the white criterion for not placing them in a threatened category.