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Dolichopodidae (Diptera: Empidoidea) I. Ya. Grichanov All-Russian Institute of Plant Protection, Podbelskogo 3, St. Petersburg, Pushkin 189620, Russia: e-mail: grichanov@mail.ru

All-Russian Institute of Plant Protection, Podbelskogo 3, St. Petersburg, Pushkin 189620, Russia: e-mail: grichanov@mail.ru
 

Abstract

The majority of Dolichopodidae species collected on the Brandberg have been trapped in light traps as compared to Malaise traps and yellow pan traps. Eight Brandberg species represent only a small fraction of the Namibian fauna. They comprise 7 dolichopodid genera and 5 subfamilies viz. Diaphorinae, Hydrophorinae, Medeterinae and Sympycnynae. Trap samples have been much more numerous in the surrounding Namib plains than on the Brandberg itself. Both species of Medetera have been trapped from high altitudes only.

BIOGEOGRAPHY & EVOLUTION

The known world Dolichopodidae fauna is very large, with approximately 6500 species and 200 genera. These mostly predatory flies are distributed throughout the world including the tropics and high-latitude islands.

At present a total of more than 600 Afrotropical species are known to occur. Many species described earlier this century were incompletely described, some lacking male descriptions or were inadequately illustrated. Authors, in their descriptions, often omitted important characters regarded today, as having generic level value. For this reason no less than 50 species are waiting to be synonymized or to be declared Nomina Dubia in future revisions of type material. Several hundred species probably await description. The majority of the Afrotropical species were described by Th. Becker, C.H. Curran, I.Ya. Grichanov, C.G. Lamb, O. Parent and P. Vanschuytbroeck (see Dyte & Smith 1980; Grichanov 1997, 1998a, 1998b, 1998c, 1999 et al.).

The fauna of the Congo basin (Kinshasa) may be regarded well-known, while fragmentary investigations have been undertaken of the fauna of South Africa, Madagascar, Tanzania, Uganda, Nigeria, Kenya and Cameroon. Adjacent African islands and other Afrotropical countries have been poorly studied.

NAMIBIAN DISTRIBUTION

Until recently, very little information was available, with respect to the Namibian Dolichopodidae. Twenty species were recorded and described in recent reviews of Afrotropical genera and subfamilies of the family (Grichanov 1997, 1998a, 1998b, 1998c, 1999 et al.). The majority of species have been collected in the central arid part of the country, being xerophilous and halophilous by nature. Some of these species are widely distributed across semi-deserts or maritime territories of the Old World (Amblypsilopus munroi (Curran, 1924), Hydrophorus praecox Lehmann, 1822, Tachytrechus tessellatus (Macquart, 1842), Thinophilus indigenus Becker, 1902). The remaining species are endemic to Namibia (Medetera chumakovi Grichanov, 1997, Medetera rikhterae Grichanov, 1997, Thinophilus munroi setiscutellatus Grichanov,1997) or to southern part of Africa (Cemocarus griseatus (Curran, 1926), Hydrophorus vaalensis Parent, 1954, Medetera norlingi Grichanov, 1997, Medetera polleti Grichanov, 1997, Medetera subchevi Grichanov, 1997, Condylostylus imitator Curran, 1924). Namibia as a whole and north-eastern parts of the country (Kwando river basin), has a significant tropical element, with many species common with Central Africa or occurring across the continental Afrotropics. To date I have examined about 50 species of the family collected in Namibia, some of which should be described as new taxa, but the real number may reach 100-200 species following a special expedition covering a wider geographical area of the country.

BIOLOGY AND SAMPLING TECHNIQUES

Most adult dolichopodids occur on sand, damp ground, grass, leaves, tree trunks, river rocks, and other surfaces near open water. These sites are utilised both for mating and opportunistic feeding on soft-bodied invertebrates. Adult flies are predaceous on small mites (Acari), Aphidae (Homoptera), Psyllidae (Homoptera), Psocoptera, Thysanoptera, Nematocera (Diptera) and other insects, sometimes playing some regulating role in agricultural ecosystems. Most of the numerous species of the cosmopolitan genus Medetera Fisher von Waldheim, 1819 are associated with tree trunks, especially in boreal forests of the Holarctic Region, where their larvae are predacious on bark-beetles (Coleoptera) and other insects – tree pests. Imagoes of many Medetera species may be encountered in montane regions on large stones and rocks covered by mosses and lichens and in semi-desert regions in and around rodent burrows and other ground cavities. A great many species of Dolichopodidae may be collected by use of Malaise and light traps, or by sweeping through vegetation with a net. Larvae of almost all species studied are predators inhabiting moist substrata. Small-sized species may be saprophages in larval stage. Species of only one genus (Thrypticus Gerstaecker, 1864) are known as phytophages living inside stems of cereal grasses.

Many rare species are known only from their type localities. When such species are only known from small blocks of remnant or disturbed vegetation, their long-term survival is more problematical, especially in highly altered agricultural and urban districts. They may be threatened, if their remnant habitats are degraded by burning, grazing, clearing or invasion by exotic weeds, replaced by settlements, roads and other anthropogenic landscapes. Active application of chemical plant protection means, land reclamation, changes in land use technologies towards more rationalized approaches can have adverse effects on the biodiversity of natural ecosystems.

Evolutionary perspective regarding inselbergs

There are no published accounts of altitudinal zonation of montane territories, regarding Dolichopodidae. My personal observations of the fauna of the Caucasus and Tyan Shan mountain ranges, have revealed that the species diversity increases at a height from 1500 to 2000 m in comparison with the surrounding steppe and desert plains. However, the number of species decreases in the alpine zone at a height more than 3000 m, though some species may be most abundant on alpine meadows and swamps. The low Polar and North Ural Mountains exhibit a significant decrease in species diversity at a heights of 500-800 m as compared to the adjacent tundra plain.

RESULTS AND ANALYSIS

Collection methodology (effectiveness)

The majority of Dolichopodidae collected on the Brandberg were trapped using automatic light traps. One of the traps, situated near a spring, was especially rich, with 188 specimens and 5 species, though only one species (Hydrophorus praecox) was significantly abundant. In this case, the light trap was situated in a sparsely vegetated river Valley (Bushy Karoo-Namib shrubland) at a height 700 m. The other trap samples were not significantly numerous. Only one specimen was collected by the use of yellow pan traps.

Species richness

The majority of Dolichopodidae species collected on the Brandberg were trapped in light traps (7 species) as compared to Malaise traps (3 species) and yellow pan traps (1 species). Eight Brandberg species represent only a small fraction of the Namibian fauna. They comprise 7 dolichopodid genera and 5 subfamilies viz. Diaphorinae, Hydrophorinae, Medeterinae and Sympycnynae. The true number of species may be at least three times as many. For example, an occasional trapping at Ugab River, 2 km W of Brandberg Wes by use of Malaise trap has given three more species belonging to an additional 2 genera of the family (Micromorphus sp. and Cryptophleps sp.).

Altitudinal zonation:

An experiment carried out has shown that trap samples were much more numerous in the surrounding Namib plains (Messum River/Valley, Ugab River sites) than on the Brandberg itself. A single 3-days trap sample at Ugab River contained 37 specimens of 4 species, one of which (one female of Asyndetus virgatus Curran, 1926) was also trapped at a height 1180 m. One hundred and ninety specimens of 5 species were found in a long-term trapping from Messum Valley (700 m) and only 23 specimens of 3 species at high altitudes (1950-2470 m). It is interesting to note that both species of Medetera (known also from South Africa) are absent in trap samples from the surrounding Namib plains. Hydrophorus praecox was trapped at four altitude levels (from 700 to 2470 m), but this is not surprising, as the species is considered ubiquist, inhabiting various water reservoirs and springs on plains, in alpine zones and along sea coasts all over the World (with the possible exception of the Americas). The species is now known from many localities in Namibia and is pan Africa.

Taxonomy/Systematics

Two new species were discovered in samples from the Brandberg Pilot Study. They are not endemic to the mountain and shall be described elsewhere.

Discussion

The small number of effective samples during the first stage of the Brandberg survey does not allow any reasonable conclusions to be drawn, with respect to species dominance or altitudinal zonation.

Dolichopodidae inhabiting arid territories are known to represent ephemeral elements of native faunas, strongly dependant upon precipitation and longevity of the rainy season. They distribute, with a more or less even density of population, immediately following heavy showers, aggregating, often in great numbers, around small rivulets and ephemeral pools several days or weeks later, when the ground is becoming dry. Such ephemeral pools might serve a cause for unusually high catches of flies from 22 to 24 October, 1998 at Ugab River and at 3 of April, 1999 at Messum Valley. Displacing a trap by 1-3 m outside a pool margin might significantly alter the number of flies trapped. The Brandberg is characterised by temporary to semi-permanent ephemeral pools on granite slabs, or in ephemeral river beds. Such habits may well provide suitable breeding areas for Dolichopodidae following heavy precipitation. The Ugab River sites are a quite different habitat from even the lower slopes of the Brandberg massif. The Ugab River, though ephemeral in nature, is considerably more and differently vegetated than the Hungorab ravine, and has a series of permanent springs, which would obviously greatly effect species richness.

The presence of two species of the xerophilous genus Medetera, in 6 samples from high altitudes appears to be very interesting. The subfamily Medeterinae is the most diverse in southern Africa, in contrast to the Sciapodinae with its great number of species in Central Africa. Species of Medetera are the most important dolichopodid element in arid biomes within Namibia and I suspect that further investigation of the Brandberg massif will reveal at least 10 more species of the genus.

Acknowledgements

I am sincerely grateful to Ashley H. Kirk-Spriggs for loaning the material of the Namibian Museum and his helpful suggestions, of which quite a number were incorporated in the paper. The work was carried out in Brussels, in the laboratory of Patrick Grootaert (Institut royal des Sciences naturelles de Belgique), and was financially supported by Belgian Office for Scientific, Technical and Cultural Affairs (1999-2000).

References

DYTE, C.E. & SMITH, K.G. 1980. Family Dolichopodidae. In R.W. CROSSKEY (ed.). Catalogue of the Diptera of the Afrotropical Region. British Museum (Natural History), London: 443–463.

GRICHANOV, I.Ya.1997. A brief review of the Afrotropical fauna of the subfamily Hydrophorinae (Diptera: Dolichopodidae) with description of Cemocarus stuckenbergi sp.n. International Journal of Dipterological Research, 8(3): 149--157.

GRICHANOV, I.Ya. 1998a. Afrotropical species of the genus Tachytrechus HALIDAY (Diptera: Dolichopodidae). International Journal of Dipterological Research, 9(2): 115-122.

GRICHANOV, I.Ya. 1998b. Afrotropical species of the genus Lichtwardtia ENDERLEIN (Diptera: Dolichopodidae International Journal of Dipterological Research, 9(3): 221-236.

GRICHANOV, I.Ya. 1998c. New data on Sciapodinae (Diptera: Dolichopodidae) with a revised catalogue and keys to Afrotropical species. Bulletin de l’Institut royal des Sciences naturelles de Belgique, Entomologie, 68: 79-130.

GRICHANOV, I.Ya. 1999. A brief review of the Afrotropical fauna of the subfamily Medeterinae (Diptera: Dolichopodidae) with descriptions of a new genus and new species. Bulletin de l’Institut royal des Sciences naturelles de Belgique, Entomologie, 69.

Flies of the family Dolichopodidae are often abundant in moist habitats and are frequently found on foliage, tree trunks, mud flats, and river rocks. Adults are predaceous on soft-bodied invertebrates and serve as important general control agents of many pest species.

The maggotlike larvae are found in such habitats as soil, rotted vegetation, mud, and under bark. Most are predators or scavengers, although the larva of Thrypticus is a phytophagous stem miner in various Monocotyledons [see Dyte (1967) for review of immature stages]. Williams' (1938b,c, 1939) studies of the immature stages of Hawaiian dolichopodids are among the best documented for the family.

The elaborate secondary sexual characters of male dolichopodids are assumed to aid in species recognition during courtship and often show parallel development in unrelated groups. These characters include flaglike flattening of the arista and tarsi, strongly modified setae and cuticular projections, prolongation and deformation of podomeres, orientated silvery pruinosity, maculation and deformation of wings, etc. The hypopygium is often greatly enlarged and exposed and usually carries species-specific characters. The tiny Babindella, of the endemic Australian subfamily Babindellinae, shows secondary postabdominal symmetry (Bickel 1987b).

The Dolichopodidae is one of the most diverse families of flies, with approximately 5,000 described species. In the Australasian/Oceanian Regions, 995 species representing 77 genera in 9 subfamilies are currently known, although many new species and genera await description, especially from Australia and the Melanesian Archipelago. Apart from southern temperate elements in New Zealand and Australia, much of the Australasian/Oceanian fauna has strong affinities with that of the Oriental Region. A notable exception is the presence of the Neotropical Condylostylus longicornis in eastern Polynesia.

Some "tramp" species, such as Medetera grisescens and Chrysosoma leucopogon, show extraordinarily widespread distributions throughout both the Oriental and Australasian regions, including many isolated oceanic islands. Several brachypterous species are known from subantarctic islands. Of particular interest is the extensive speciation of Campsicnemus in the Hawaiian Islands (138 spp., with many more awaiting description). This radiation invites comparison with that of the well-studied Hawaiian Drosophila.

The subfamily arrangements followed here are based on Ulrich (1981), with modifications. The limits of certain subfamilies, such as the Diaphorinae and Sympycninae are unclear and some genera, such as Sympycnus, are polyphyletic assemblages. Recent revisionary studies on the Medeterinae (Bickel 1986a,b,c, 1987c) and Hydrophorinae (Grootaert & Meuffels 1984, Meuffels & Grootaert 1984) have added to the regional understanding of these taxa.

Becker's (1922b) monograph, although dated, remains the basic reference for both the Oriental and Australasian/Oceanian regions. Important faunistic treatments include those on the Hawaiian Islands (Hardy & Kohn 1964, Tenorio 1969), New Zealand (Parent 1933b), Australia (Hardy 1930a, 1935b, 1939c; Parent 1932a, 1933a), Samoan Islands (Lamb 1929), and New Guinea (de Meijere 1906b, 1913a,b, 1915b; Parent 1939a). Additional species descriptions are found in the many papers of Parent. Robinson & Vockeroth (1981) provided a well-illustrated general review of the family.

Dolichopodids, commonly called long-legged flies, are found worldwide and consist of over 5,000 species in some 150 genera. Adults and most larvae are predaceous on other insects and small invertebrates. Adults of extant forms inhabit moist, cool, sylvan habitats near water sources where they can be found resting on tree trunks, vegetation, or skating on the water surface in pursuit of prey items. Larvae are found in rotting vegetation, wet soil, and under bark where they are scavengers or predators.
 

The Dolichopodidae are well represented in the fossil record, especially as amber inclusions. Although only Baltic amber material of this family has been described to any extent, the family is present in most other faunas as well (Spahr, 1985). Many adults of this family are tree associates and patrol up and down trunks in search of both mates and food. Hence, they are especially susceptible to being entrapped in tree resins and fossilized in amber. Modern trunk-associated dolichopodids include: most Medeterinae (especially Medetera Fischer von Waldheim and Systenus Loew), all Neurigoninae, Achalcus Loew, many Sciapodinae (especially Sciapus Zeller s. str.), and some Diaphorinae. All of these taxa also occur in Baltic amber.
 

As seen in Baltic amber faunas generally (Larsson, 1978), most recent insect families had radiated by the Early Tertiary. This is the case with the Dolichopodidae, and genera appear well defined and essentially modern at that time. However, the Baltic amber fauna described by Meunier is badly in need of revision, especially in light of large unworked collections of fossils in many institutions. Particular attention must be paid to Meunier's generic concepts and species placements.
 

In addition to the determined material listed below, undetermined material of this family has been recorded from the Upper Cretaceous ambers of Canada (McAlpine & Martin, 1969: 837) and Siberia (Zherichin & Sukacheva, 1973: 18, 37), the Oligocene/Miocene amber of the Dominican Republic, and Miocene amber of Chiapas, Mexico (Poinar, 1992), the Lower Miocene deposits of Sado Island, Japan (Fujiyama, 1985: 43), the Miocene Bitterfeld amber of Germany (Schumann & Wendt, 1989), and the Eocene/Oligocene deposits of the Bembridge Marls on the Isle of Wight (Jarzembowski, 1976: 12).

Ref.: Meunier (1907c­j,1908a­d, f, review of Baltic amber taxa).

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