Insecta: Diptera, Stratiomyidae

798 Freshwater Invertebrates of the Malaysian Region Insecta: Diptera, Stratiomyidae Damir Kovac1 and Rudolf Rozkošný2 1 Senckenberg Research Institute and Natural History Museum, Senckenberganlage 25, D-60325 Frankfurt, Germany (Email: damir.kovac@senckenberg.de) 2 Department of Zoology and Ecology, Faculty of Science, Masaryk University, Kotlárská 2, 611 37 Brno, Czech Republic (Email: rozk@sci.muni.cz) INTRODUCTION The Stratiomyidae or soldier flies have a worldwide distribution and comprise 2651 described species (Woodley 2001). The adult flies are about 2–20 mm long and of very diverse colour and appearance. The brightly coloured or metallic species sometimes resemble wasps or bees. The wing venation is characteristic for the family: the anterior veins are strong, the discal cell is small and usually situated in the anterior half of the wing (Fig. 1A). The antennae show a large structural variation (Fig. 1B–G) and are useful for the identification of genera. The scutellum is often adorned with spines (Fig. 1A), which may be the reason for the common name soldier flies. The larvae are characteristically and uniformly built. The body is flat and composed of a strongly sclerotized head capsule, three thoracic and eight abdominal body segments. The cuticula has a honeycomb or mosaic appearance originating from calcium carbonate excretions of the larvae. The mandibles are fused with the maxillae and form two characteristic mandibular-maxillary complexes, which are moved alternately in a vertical plane. Terrestrial larvae are elongate-oval and usually have a rounded anal (last abdominal) segment (Fig. 1H). Aquatic or semiaquatic larvae are often characterized by a more or less tapering posterior end which bears an apical coronet of plumose hydrofuge hairs (Fig. 1J–L). The Stratiomyidae are of minor economic or medical importance. The larvae of Hermetia illucens (Hermetiinae), a species of American origin also occurring in Southeast Asia, may occasionally cause myasis (infestation of body tissues by the larvae) in man (Leclercq 1969). This species also breeds in rotten fruits or cadavers and can be used as a bioindicator in forensic entomology (e.g. to determine postmortem interval in criminal cases). The aquatic larvae of Stratiomyidae sometimes occur in large numbers in ponds and may be of importance as food for fish. Oxycera larvae occurring in clean running waters can indicate water quality. General information about Stratiomyidae can be found in James (1975, 1981), Oosterbroek (1998), Rozkošný (1973, 1982, 1983, 1997, 2000) and Wesenberg-Lund (1943). Insecta: Diptera, Stratiomyidae 799 GENERAL BIOLOGY Adult stratiomyids are often encountered resting on plants near their breeding sites. The larvae of most subfamilies are terrestrial and breed in decaying plant and animal matter, under the bark of dead trees or in excrement. The aquatic larvae occur in all types of freshwater habitats. Larvae of Stratiomys, Oplodontha and most Odontomyia (Stratiomyinae) live at the margins of ponds, lakes, spring pools, marshes, slowlyflowing waters with rich vegetation, in rock-pools along streams, on wet surfaces of Figure 1. Morphological features of the adults and habitus of the aquatic larvae of Stratiomyidae. A – adult Odontomyia; B–G antennae of the adults: B – Beris, C – Odontomyia, D – Oplodontha, E – Stratiomys, F – Oxycera, G – Ptecticus; H–L, aquatic larvae: H – Beris, I – Nemotelus, J – Oxycera, K – Odontomyia, L – Stratiomys. (Source: all redrawn after Rozkošný 2000 except G) 800 Freshwater Invertebrates of the Malaysian Region rocks splashed by waterfalls or in phytotelmata. Oxycera (Clitellariinae) larvae usually live in hygropetric situations (i.e. in a thin film of water) at the margins of springs and streams, for example, in wet moss or on moist rocks in running water. However, some also occur in stagnant water or even are terrestrial. Larvae of some Beris (Beridinae) are semi-aquatic and live in moist moss along springs and streams. Some aquatic stratiomyids can endure the high salinity of salt marshes and sea coast or the high temperatures of hot springs reaching 40–54 °C. Some adult Stratiomyidae are apparently nectar feeders as indicated by an elongate proboscis with narrow labella, e.g. in Nemotelus. However, many species have a rather short proboscis with large fleshy labella and probably swallow pollen grains (Olroyd 1969) or utilize honeydew (Beuk 1990). Larvae of Stratiomyidae are exceptional among the lower Brachycera, because they are not predatory or parasitic. They feed on detritus and use their specialized mouthparts as a sweeping apparatus. The process of filtration and grinding in the foregut was described in detail by Schremmer (1951a). Aquatic larvae feed on decaying leaves, detritus, algae and the microorganisms associated with this food. Oxycera larvae feed on algae growing on moist rocks. In the gut contents of freshly captured European Oxycera pardalina Schremmer (1951b) found algae of 12 genera belonging to Cyanophyceae, Conjugatae, Chlorophyceae and Diatomeae. Typical aquatic stratiomyid larvae like Stratiomys and Odontomyia stay in shallow water with their terminal plumose hairs spread on the water surface. These hydrofuge hairs keep the larvae attached to the surface and prevent the water from entering the respiratory chamber. In response to vibrations the animals glide downwards with the terminal hairs enclosing an air bubble. When the air bubble is eversed the larvae´s buoyancy increases and the larvae will rise toward the water surface again. The mouthparts can be moved rapidly in a vertical direction and in some species are used as propulsive organs. Some species living in flowing waters (e.g. Oxycera) have backward-pointing spines on their body segments with which they become anchored in algal threads thus preventing them from drifting away with the water current. Life cycle There is no information about the life histories of Oriental stratiomyids, except of the paper of Mathur (1933), who deals with some aspects of the life history of Odontomyia cyanea. Temperate aquatic species lay their eggs mostly in conspicuous oval masses (about 13 mm long in Stratiomys), cemented together by a secretion. The eggs are usually pale yellow, elongate and about 1 mm in length. The Stratiomys female is able to lay more than 600 eggs during several hours. The time required for hatching varies from 5–20 days. The number of instars is not known in the aquatic species. In temperate regions the life cycle is annual or the larvae may hibernate several times. Insecta: Diptera, Stratiomyidae 801 Figure 2. Morphological features of the larvae. A – dorsal anal segment of Beris; B – dorsal anal segment of Nemotelus; C – abdominal segment 3 of Beris; D – abdominal segment 3 of Ptecticus; E – head of Oplodontha, dorsal view; F – head of Oxycera, dorsal view; G – last abdominal segments of Oplodontha, ventral view; H – head of Odontomyia, lateral view; I – head of Oplodontha, lateral view. (Source: all redrawn after Rozkošný 1997 and 2000 except D) 802 Freshwater Invertebrates of the Malaysian Region Pupation occurs within the last larval skin (puparium), which retains the characters of the larvae, but is usually more rigid. The pupa is often much smaller than the puparium and may occupy only its anterior third. The empty space is filled with air and the puparium floats on the water surface (Stratiomys and Odontomyia). In the laboratory the time required for pupal development of some European species of Odontomyia, Oplodontha or Stratiomys is 5–7 days at room temperature. Adults emerge through a T-shaped longitudinal slit along the anterodorsal part of the puparium. REGIONAL TAXA Our knowledge of aquatic Stratiomyidae in Malaysia and Singapore is very poor. According to the recent catalogue of Woodley (2001) only Odontomyia notatifrons and O. latitibia have been recorded from this region. Odontomyia latitibia was found in water-filled internodes of decaying bamboo culms in Sabah (Rozkošný and Kovac 1994). In addition, we have recorded O. pulcherrima from Peninsular Malaysia and Sabah. The larvae of this species live on wet surfaces of rocks splashed by waterfalls (Rozkošný and Kovac 2001). Furthermore, we have found that larvae of Ptecticus flavifemoratus, although belonging to an otherwise terrestrial group have aquatic larvae. They develop in water-filled stumps of young bamboo shoots (Rozkošný and Kovac 1996, 1998). Other (unpublished) records include Odontomyia ochropa, O aurata, O. lutatius, O. fascipes and Oplodontha rubrithorax, which were collected by D. Murphy in Singapore. A key to the adults of the Oriental Oplodontha was given by James (1947). Many Stratiomyidae are good fliers and widely distributed. For example, O. rubrithorax was recorded from India, Sri Lanka, Thailand, the Philippines, Japan (Ryukyu Islands), Singapore, Indonesia (Java) and even from the Afrotropical Region (Zaire) (Woodley 2001). Therefore, it is probable that various genera and species of aquatic Stratiomyidae recorded from other parts of the Oriental region also occur in Malaysia, for example, species of Stratiomys or Oxycera, which are known from India or Myanmar as well as from Java. For this reason, we have included some genera in our key which have not yet been recorded from Malaysia. For most Oriental stratiomyids the larvae have not yet been described. There is only a preliminary key to the Oriental larvae of Odontomyia (Rozkošný and Kovac 2001). It contains only four out of 25 known Oriental species. Therefore, larvae collected in the field should as often as possible be reared to the adult stage. In general, rearing of stratiomyid larvae is easy, especially if older instars or puparia are collected. The larvae of Odontomyia and Stratiomys can be reared in aquaria containing shallow water, aquatic plants and a sufficient amount of organic detritus. Odontomyia and Stratiomys usually pupate on the water surface, Beris, Nemotelus and Oxycera on land. The adults of aquatic stratiomyids can be collected by sweeping vegetation near the margins of ponds and streams. Insecta: Diptera, Stratiomyidae 803 KEY TO GENERA OF AQUATIC LARVAE 1. Last abdominal segment rounded posteriorly or angulate, without apical coronet of plumose hairs (Fig. 1H,I) ...................................................................................................................... 2 - Last abdominal segment subquadrate, conical or tube-like, always with apical coronet of plumose hairs (Fig. 1J–L) ...................................................................................................... 4 2. Last abdominal segment bipartite in dorsal view, bilobed posteriorly; each lobe with long subapical seta (Fig. 2B) ............................................................................ Nemotelinae: Nemotelus* - Last abdominal segment semi-circular (Fig. 2A) or trapezoid. .............................................. 3 3. Dorsal setae on body segments in groups (Fig. 2C) ...................................... Beridinae: Beris - Dorsal setae on body segments single (Fig. 2D) ....................................... Sarginae: Ptecticus 4. Antenna situated between anterolateral angle of head capsule and eye prominence (Fig. 2F).. .......................................................................................................... Clitellariinae: Oxycera** - Antenna situated at anterolateral angle of head capsule (Fig. 2E) ................... Stratiomyinae ..5 5. Last abdominal segment elongate tube-like (Fig. 1L); posterior margin of abdominal segments always without ventral hooks ................................................................................. Stratiomys - Last abdominal segment oblong or slightly conical (Figs. 1K, 2G); if rarely elongate, then penultimate abdominal segment with strong ventral hooks (Fig. 2G) ................................... 6 6. Posterior ventral seta on head bush-like (Fig. 2I); abdominal segments covered dorsally with scale-shaped, apically dilated hairs ....................................................................... Oplodontha - Posterior ventral seta on head simple or at most pubescent (Fig. 2H); abdominal segments without apically dilated hairs ............................................................................... Odontomyia * Nemotelus was not recorded from the Oriental region. However, other genera of Nemotelinae are present in the Oriental Region. Their larvae are not known, but they may be semi-aquatic like the larvae of Nemotelus ** belongs to Stratiomyinae after Woodley (2001) REFERENCES Beuk P.L.T. 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