Insecta: Diptera, Empididae

Transcription

1 Insecta: Freshwater Diptera, Invertebrates Empididae of the Malaysian Region 805 Insecta: Diptera, Empididae Patrick Grootaert Royal Belgian Institute of Natural Sciences, Vautierstraat 29, B-1000 Brussels, Belgium ( INTRODUCTION The Empididae sensu stricto or true dance flies are small (2 mm) to large flies (15 mm), dark to yellow and generally with a sclerotized proboscis. They are very diverse in habitus (see Fig. 2) and have as a common characteristic a small indentation in the eye border at the level of the insertion of the antenna. They form a large family with an enormous radiation in the Palaearctic region. They are far less common in the tropics and will thrive only in mountainous areas. In the Malaysian region we expect the genera Hilara, Empis (Coptophlebia), Rhamphomyia which do not have true aquatic larvae and the Hemerodromiinae Hemerodromia, Chelifera and Clinocera which do have aquatic larvae. It is doubtful that other Palaearctic genera such as Chelipoda, and Wiedemannia are present here. GENERAL BIOLOGY The genus Hilara (Fig. 2A), an old dance fly genus that radiated in temperate regions, has an epigamic behaviour (to attract mates) associated with water bodies, but the larvae live mainly in the soil. The male hunts for small prey floating on the surface of pools, ponds, brooks or streams (Fig. 1). It picks up the prey and often wraps it in a silk cocoon, which is produced by silk glands in the enlarged fore basitarsi. Eventually the male carrying the cocoon joins a female swarm. Females tend to inspect the male with its present and when the female dives under the male to grab the prey, the male grabs the female s thorax and mating starts. Generally, the couple leaves the swarm for some vegetation. This behaviour is specific and has a number of variants. Light intensity of the area (Grootaert 1994) determined by the coverage of the canopy, the presence of markers in the landscape, the type of water surface (running or still, size) all determine where the male hunts and where female swarms are formed. Females sometimes swarm above water, but also terrestrial swarms are formed some distance from the place where the males hunt. Generally, the females fly in a horizontal plane in a rapid to-and-fro movement. However, triangular swarms are known as well, where the females dance up in a slow motion and at the top of the triangle, dive down vertically, and fly in a horizontal direction back to the point of departure and dance

2 806 Freshwater Invertebrates of the Malaysian Region Figure 1. Swarming behaviour of Hilara dance flies occurring in the gallery forest above the small streams. The male catches a prey floating on the water surface and enrobes it with silk. Eventually the male joins a swarm of females. The female inspects the offer, dives down below the male and grabs the cocoon while the male attempts mating. Figure 2. A Hilara isaanensis male (d: discal cell; arrow points to the upper branch of the fork); B Hemerodromia sp. from Northeast Thailand; C Empis (Coptophlebia) sp. from Thailand. (Arrow points to the upper branch of the fork)

3 Insecta: Diptera, Empididae 807 upwards again. The length of the swarm is limited by light zones (light-shade transition) and by location markers such as branches or vegetation. The genus Hemerodromia is associated with fast flowing streams and is predacious (Fig. 2B). The adults are small (3 5 mm), yellow or black coloured, and they are mainly active on boulders covered with moss or in the splash zone. They are present throughout the year and quite common. Their habitat is the small streams shaded by the gallery forest. This genus too is very sensitive to changing light conditions. Removing the evergreen gallery forest around the streams will destroy the populations of Hemerodromia. Empis (Coptophlebia) and Rhaphomyia are nectar feeders and can be caught when sweeping the vegetation. They are not associated with water. The larval stages of Empididae are usually found in soil, decaying wood, leaf litter and mosses, but some are aquatic. All are predacious. The larvae of Hemerodromia and Clinocera develop in the hyporheic zone of fast flowing streams at more than 10 cm under the water surface. They wander around in coarse substrate with a low content of silt, sometimes under loose rocks, in search of chironomid and simuliid lavae to prey on (Vaillant 1951, 1967; Vaillant and Gagneur 1998). The Hemerodromiinae take oxygen directly from the water while most other higher flies have to take oxygen out of the air with their spiracles. REGIONAL TAXA To our knowledge, there are no studies of aquatic empidids of Malaysia and knowledge of the Southeast Asian fauna on the whole is very poor (Smith 1975). Five species of Hilara have been described recently from Thailand (Grootaert and Verapong 2001) and eight Hemerodromiinae are known from Xishuangbanna (Yunnan, South China) (Grootaert et al. 2000), but it is doubtful that these species occur here. Six Hemerodromiinae are known also from Java: one Clinocera (Kowarzia), two Chelipoda and three Hemerodromia species. An intense search during three days in Endau-Rompin Park revealed the presence of only two Hemerodromia species (Grootaert in litt.). No larvae have been described yet from Southeast Asia and many adults are yet to be described as well. Since many species are indicators of environmental conditions and exhibit a zonation in the streams, research on their ecology is recommended in terms of site quality assessment studies. KEYS TO GENERA Identification of adults is done under a stereoscopic microscope. The genera can be recognized on the basis of the wing venation and the shape of the antennae. To identify to species level, the male secondary sexual characters are very characteristic as well as the structure of the male genitalia. Therefore preparation (dissection,

4 808 Freshwater Invertebrates of the Malaysian Region macerating in potassium hydroxide, mounting on slides) of the genitalia is necessary. The females are also characteristic but few authors have described them. So few keys allow the identification of females. The following key is limited to the empidid species associated with water bodies or marshes, except otherwise mentioned. Key to genera occurring along streams and ponds in Southeast Asia: adults 1. Fore legs raptorial: femora thickened with ventral spines (Fig. 2B) Fore legs not raptorial: femora of the usual shape Wing with discal cell (cf. Fig. 2A)... Chelifera - Wing without discal cell (Fig. 2B); running on rocks and boulders... Hemerodromia 3. Fourth vein not forked (nectar feeder not really associated with water)... Rhamphomyia - Wing with fourth vein forked (Fig. 2A,C) No proboscis, but thick lips (labellae) like in dolichopodids... Clinocera - Proboscis with a long pointed labrum (Fig. 2A,C) Proboscis long and slender (much longer than height of head, Fig. 2C); angle of fork on fourth vein acute, upper branch straight (Fig. 2C); 6 th vein not reaching the wing border (Fig. 2C); nectar feeder not associated with water... Empis - Proboscis short and stout (generally shorter than head is high; Fig 2A): angle of fork wider with upper branch elongated S-shaped (Fig. 2A); swarming above water bodies... Hilara Key to genera occurring along streams and ponds in Southeast Asia: larvae The larvae are very small, 3 6 mm when fully grown and have a whitish to yellowish colour. Hemerodromia larvae are dark pigmented. 1. Larvae amphipneustic with distinct posterior spiracles, without ventral pseudopods; terminal abdominal segment posteriorly rounded with a short tooth-like extension (Fig 3A arrow) Hilara, Empis, Rhamphomyia - Larvae apneustic (without respiratory spiracles), with conspicuous ventral abdominal pseudopods (Fig. 3B,C) Terminal abdominal segment posteriorly at most with small tubercles, each with a few long setae (otherwise the larva looks like the one of Hemerodromia)... Chelifera - Terminal abdominal segment with prominent posterior processes Terminal abdominal segment with a pair of large ventral pseudopods (Fig. 3C). Pupa (Fig. 3E) with long, thin lateral processes... Hemerodromia - Terminal abdominal segment with both dorsal and apical processes and a shorter ventral pseudopod (Fig. 3B)... Clinocera

5 Insecta: Diptera, Empididae 809 Figure 3. A Hilara larva (arrow indicates position of posterior spiracles and tooth-like projection); B Clinocera larva; C. Hemerodromia larva (p: pseudopods); D Clinocera head; E Hemerodromia pupa. Scale 1 mm. (Source: after Niesiolowski) REFERENCES Grootaert P. (1994) Biodiversity in insects Speciation and behaviour in Diptera. Proceedings Congress on Biodiversity. In Hoffman M. and Van der Veken P. (Eds) Proceedings of the Symposium on Biodiversity: Study, Exploration, Conservation, Ghent, 18 November Pp Grootaert P., Ding Yang and Saigusa T. (2000) Empididae (Diptera: Empidoidea) from Xishuangbanna, Yunnan (I): Hemerodromiinae. Bulletin van het Koninklijk Belgisch Instituut voor Natuurwetenschappen. Serie Entomologie 66: Grootaert P. and Kiatsoonthorn V. (2001) First records of the dance fly genus Hilara in Thailand with the description of five new species. Natural History Bulletin of the Siam Society 49: Smith K.V.G. (1969) The Empididae of southern Africa. Annals of the Natal Museum 19: Smith K.V.G. (1975) Superfamily Empidoidea Family Empididae (Empidae, Hybotidae). In Delfinado M.D. and Hardy D.E. (Eds) A Catalog of the Diptera of the Oriental Region. Volume II. Suborder Brachycera through division Aschiza, suborder Cyclorrhapha. University Press of Hawaii, Honolulu. Pp Vaillant F. (1951) Un empidide destructeur de simulies. Bulletin de le Société Zoologique de France 76: Vaillant F. (1967) La répartition des Wiedemannia dans les cours d eau et leur utilisation comme indicateurs de zones écologiques. Annales de Limnologie 3: Vaillant F. and Gagneur J. (1998) The Diptera Empididae Hemerodromiinae from western Algeria and the Middle Atlas of Morocco. Annales de la Société Entomologique (N.S.) 34: