Characteristics and Natural History of Dolichopodidae s.str.

by Scott E. Brooks

Diversity

The Dolichopodidae s.str., or long-legged flies, are one of the most diverse families of Diptera with over 6600 described species (Grichanov unpublished data) and over 200 genera (Grichanov 1999) worldwide. Dolichopodids are widespread and are found in all zoogeographic regions (Robinson 1970; Dyte 1975; Dyte and Smith 1980; Bickel and Dyte 1989; Negrobov 1991; Pollet et al. 2004). In America north of Mexico there are about 1300 described species and 57 genera (Pollet et al. 2004; Brooks et al. 2005).


Argyra sp. (photo by S.A. Marshall)	Male Chrysotus sp., with enlarged palps (photo by S.A. Marshall)

Diagnosis and recognition

Adult dolichopodids range in size from about 1-9 mm in length and can be recognized by their elongate legs, reduced wing venation, aristate antennae, and relatively slender build. Most species are metallic greenish-blue to greenish-bronze, while some others are non-metallic yellowish (e.g., some species of Achalcus Loew, Argyrochlamys Lamb, Neurigona Rondani, Xanthochlorus Loew and Xanthina Aldrich), or brown to blackish (e.g., several species of Micromorphus Mik and Medetera Fischer von Waldheim).

Males are known for their wide array of secondary sexual characteristics which have been invaluable features for recognizing species. Male secondary sexual characteristics often include modifications of the antennae, palps, wings and, typically, the legs. The male genitalic capsule or hypopygium is either somewhat small and partially enclosed by preceding abdominal segments, or large, permanently exserted and supported by a pedunculate abdominal segment 7. Snodgrass (1904), Buchmann (1961), Ulrich (1974) and Cumming et al. (1995) have provided morphological studies of the dolichopodid hypopygium. The hypopygium of the subfamlily Dolichopodinae was treated in detail by Brooks (2005).

Larvae are whitish, cylindrical and relatively slender with distinct creeping welts on segments 4 to 11. The anterior end is tapered and the posterior end is truncate with four or more lobes on segment 12 (Robinson and Vockeroth 1981; Corpus 1986a,b, 1988). The larval head is modified posteriorly into two apically expanded or spatulate metacephalic rods and two tentorial arms, and the larval mandible is composed of four components (Woodley 1989; Sinclair 1992). Dolichopodid pupae are characterized by the possession of a pair of long, dorsal prothoracic respiratory horns and a pair of frontofacial sutures. Most known species also possess spiniferous transverse bands on the abdominal tergites (Dyte 1967; Robinson and Vockeroth 1981; Corpus 1986a,b, 1988).


Larva of Medetera signaticornis Loew (photo by J. Hulcr, http://www.insectimages.org)	Pupa of Medetera sp. (photo by G.J. Lenhard, http://www.insectimages.org)

Natural history

In general, adults and larvae prefer moist environments including stream and lake margins, humid forests, saltmarshes, seashores, and freshwater seepages, where they often occur in large numbers. Adults of some species are closely associated with tree trunks or vertical surfaces (e.g., Medetera, Neurigona, Sciapus Zeller), whereas others occur in drier habitats such as agricultural fields and grasslands (e.g., some species of Medetera and Dolichopus Latreille) or urban gardens (e.g., some species of Condylostylus Bigot). Larvae occur in mud, damp soil, leaf litter, moss, algal mats, decaying seaweed, sap wounds, under bark, in tree hole debris and within plant tissues (Dyte 1959). Before pupation the final instar spins a protective cocoon incorporating soil particles and other environmental debris, which completely encapsulates the pupa, except for the tips of the respiratory horns, which protrude from a small aperture (Dyte 1959; Corpus 1986a,b, 1988). Recent studies (Pollet 1992, 2000, 2001; Pollet and Grootaert 1991, 1996) demonstrate that dolichopodids have very specific habitat requirements and react quickly to environmental alterations, making them potentially useful as bioindicators for site quality assessment and conservation purposes.


Dolichopus sp. (photo by S.A. Marshall)	Hydrophorus sp. (photo by S.A. Marshall)

Adults are predaceous, feeding primarily on small, soft-bodied arthropods and annelids, and are important natural enemies of pests in a variety of habitats including agroecosystems. Ulrich (2005) provided an exhaustive review of literature data on predation by adult Dolichopodidae and found that the larvae and adults of Diptera are the most frequently observed prey (especially Chironomidae and Culicidae, but see comments by Ulrich 2005), followed by Homoptera, Collembola, mites and Thysanoptera. Other documented prey items include annelids, cladocerans, amphipods, small myriapods, odonate eggs, termites, psocopterans, beetle larvae (i.e. Scolytidae and Curculionidae), early instar caterpillars, dead and wounded arthropods and amphibian embryos (see references in Ulrich 2005). Although the adults of some dolichopodids (e.g., Hydrophorus Fallén, Scellus Loew, Hydatostega Phillipi, Thinophilus Wahlberg, Aphrosylus Haliday) are known to use their forelegs to hold and manipulate their prey (Roubaud 1903; Doane 1907; Williams 1939; Harmston 1948; Peterson 1960), most grab and masticate prey with their epipharynx and labellum, suck up the liquids and discard the remains (see references in Ulrich 2005). In addition to feeding on live prey, many dolichopodids have also been observed taking up honeydew, and it is thought that most species do so in order to obtain carbohydrates (Ulrich 2005). Adults of some Dolichopodinae have elongate mouthparts (e.g., Ortochile Latreille, some species of Hercostomus Loew s.l.) and are known to be anthophilous and feed on nectar (Dyte, unpublished manuscript). The morphology of the mouthparts of adult dolichopodids has been studied by Cregan (1941) and Satô (1991)


Condylostylus sp. (photo by S.A. Marshall)	Dolichopus sp. (photo by S. Ellis, http://www.forestryimages.org)

Many adult dolichopodids, especially those of the subfamily Dolichopodinae, show complex mating behaviour. Males of this subfamily often engage in mating dances which usually involve wing displays, or displays of secondary sexual characteristics (Steyskal 1938, 1946). Males of some species, e.g., Poecilobothrus nobilitatus (Linnaeus), also establish territories which they defend from conspecific males and other intruders (Lunau 1992). Males of some Hydrophorinae, e.g., Hydrophorus oceanus (Macquart), engage in mate guarding and hold on to the female with their fore legs following copulation, thus preventing other males from mating with her (Dyte 1988).

In general, little is known about the activities of dolichopodid larvae; however, most are thought to be predators or scavengers. Larvae of many species of Medetera are known to be significant predators of bark beetle larvae (DeLeon 1935; Bickel 1985). In contrast, larvae of Thrypticus Gerstäcker are phytophagous and feed as stem-miners in grasses, sedges and rushes (Dyte 1959).

References

Bickel, D.J. 1985. A revision of the Nearctic Medetera (Diptera: Dolichopodidae). U.S. Department of Agriculture, Technical Bulletin 1692: 1–109.

Bickel, D.J. and Dyte, C.E. 1989. Family Dolichopodidae. Pp. 393-418 in Evenhuis, N.L. (ed.), Catalog of the Diptera of the Australasian and Oceanian Regions. Honolulu: Bishop Museum Press, 1155 pp.

Brooks, S.E. 2005. Systematics and phylogeny of Dolichopodinae (Diptera: Dolichopodidae). Zootaxa 857: 158 pp.

Brooks, S.E., Cumming, J.M. and Pollet, M.A.A. 2005. Checklist of the Dolichopodidae s.str. (Diptera) of America north of Mexico (1st Edition). PDF document, 18 pp. Available from: http://www.nadsdiptera.org/Doid/Checklist/Dolichopodidae Checklist.pdf (accessed 18 November 2005).

Buchmann, W. 1961. Die Genitalänhange mitteleuropäischer Dolichopodiden. Zoologica 110: 1-51.

Corpus, L.D. 1986a. Biological notes and descriptions of the immature stages of Pelastoneurus vagans Loew (Diptera: Dolichopodidae). Proceedings of the Entomological Society of Washington 88: 673–679.

Corpus, L.D. 1986b. Immature stages of Liancalus similus (Diptera: Dolichopodidae). Journal of the Kansas Entomological Society 59: 635–640.

Corpus, L.D. 1988. Immature stages of Tachytrechus auratus (Diptera: Dolichopodidae). Pan-Pacific Entomologist 64: 9–15.

Cregan, M.B. 1941. Generic relationships of the Dolichopodidae (Diptera) based on a study of the mouthparts. Illinois Biological Monographs 18: 1-68.

Cumming, J.M., Sinclair, B.J. and Wood, D.M. 1995. Homology and phylogenetic implications of male genitalia in Diptera – Eremoneura. Entomologica Scandinavica 26: 121–151.

DeLeon, D. 1935. A study of Medetera aldrichi Wh. (Diptera: Dolichopodidae), a predator of the mountain pine beetle Dendroctonus monticolae Hopk., Coleoptera, Scolytidae). Entomologica Americana 15: 59-89.

Doane, R.W. 1907. Notes on the habits of Scellus virago Ald. Entomological News 18: 136-138.

Dyte, C.E. 1959. Some interesting habitats of larval Dolichopodidae (Diptera). Entomologist’s Monthly Magazine 95: 139-143.

Dyte, C.E. 1967. Some distinctions between the larvae and pupae of the Empididae and Dolichopodidae. Proceedings of the Royal Entomological Society of London, Series A, 42: 119-128.

Dyte, C.E. 1975. Family Dolichopodidae. Pp. 212-258 in Delfinado, M.D. and Hardy, D.E. (eds.), A Catalog of the Diptera of the Oriental Region Vol. 2. Suborder Brachycera through Division Aschiza, Suborder Cyclorrhapha. The University Press of Hawaii, Honolulu, 618 pp.

Dyte, C.E. 1988. Mate guarding and sex ratio in Hydrophorus oceanus (Macquart) (Diptera: Dolichopodidae). The Entomologist 107: 122-126.

Dyte, C.E. and Smith, K.G.V. 1980. 33. Family Dolichopodidae. Pp. 443-463 in Crosskey, R.W. (ed.), Catalogue of the Diptera of the Afrotropical Region. London: British Museum (Natural History), 1437 pp.

Grichanov, I. Ya. 1999. A check list of genera of the family Dolichopodidae (Diptera). Studia dipterologica 6: 327-332.

Harmston, F.C. 1948. Dipterous predators of the mosquito in Utah and Wyoming. Great Basin Naturalist 9: 21-23.

Lunau, K. 1992. Mating behaviour in the long-legged fly Poecilobothrus nobilitatus L. (Diptera, Dolichopodidae): courtship behaviour, male signalling and mating success. Zoologische Beiträge. N.F. 34: 465-479.

Negrobov, O.P. 1991. Family Dolichopodidae. Pp. 11-139 in Soos, A. and Papp, L. (eds.), Catalogue of Palaearctic Diptera. Vol. 7. Dolichopodidae - Platypezidae. Elsevier, Amsterdam. 291 pp.

Peterson, B.V. 1960. Notes on some natural enemies of Utah black flies Diptera: Simuliidae). The Canadian Entomologist 92: 266-274.

Pollet, M. 1992. Impact of enviromental variables on the occurrence of dolichopodid flies in marshland habitats in Belgium (Diptera: Dolichopodidae). Journal of Natural History 26: 621-636.

Pollet, M. 2000. Een gedocumenteerde Rode Lijst van de slankpootvliegen van Vlaanderen. Mededelingen van het Instituut voor Natuurbehoud 8. Brussels. 190 pp.

Pollet, M. 2001. Dolichopodid biodiversity and site quality assessment of reed marshes and grasslands in Belgium (Diptera: Dolichopodidae). Journal of Insect Conservation 5: 99-116.

Pollet, M.A.A., Brooks, S.E. and Cumming, J.M. 2004. Catalog of the Dolichopodidae (Diptera) of America north of Mexico. Bulletin of the American Museum of Natural History 283, 114 pp.

Pollet, M. and Grootaert, P. 1991. Horizontal and vertical distribution of Dolichopodidae (Diptera) in a woodland ecosystem. Journal of Natural History 25: 1297-1312.

Pollet, M. and Grootaert, P. 1996. An estimation of the natural value of dune habitats using Empidoidea (Diptera). Biodiversity and Conservation 5: 859-880.

Robinson, H. 1970. 40. Family Dolichopodidae. A Catalogue of the Diptera of the Americas South of the United States 40: 1-92.

Robinson, H. and Vockeroth, J.R. 1981. Dolichopodidae. Pp. 625-639 in McAlpine, J.F., Peterson, B.V., Shewell, G.E., Teskey, H.J., Vockeroth, J.R. and Wood, D.M. (eds.), Manual of Nearctic Diptera. Volume 1. Agriculture Canada Monograph 27, 674 pp.

Roubaud, E. 1903. Sur les larves marines de Dolichopodes attribuées au genre Aphrosylus (Wlkr.). Bulletin du Muséum National d’Histoire Naturelle 9: 338-340.

Satô, M. 1991. Comparative morphology of the mouthparts of the family Dolichopodidae (Diptera). Insecta Matsumurana 45: 49-75.

Sinclair, B.J. 1992. A phylogenetic interpretation of the Brachycera (Diptera) based on the larval mandible and associated mouthpart structures. Systematic Entomology 17: 233-252.

Snodgrass, R.E. 1904. The hypopygium of the Dolichopodidae. Proceedings of the California Academy of Sciences ser. 3 (Zool.), 3: 273-285, 4 pls.

Steyskal, G.C. 1938. The pre-copulatory behavior of the male of Dolichopus omnivagus Van Duzee (Diptera, Dolichopodidae). Bulletin of the Brooklyn Entomological Society 33: 193-194.

Steyskal, G.C. 1946. The mating behavior of Tachytrechus vorax, T. moechus, and Gymnopternus barbatulus (Diptera, Dolichopodidae). Bulletin of the Brooklyn Entomological Society 41: 168-169.

Ulrich, H. 1974. Das Hypopygium de Dolichopodiden (Diptera): Homologie und Grundplanmerkmale. Bonner Zoologische Monographien 5: 1-60.

Ulrich, H. 2005. Predation by adult Dolichopodidae (Diptera): a review of literature with an annotated prey-predator list. Studia dipterologica 11: 369-403.

Williams, F.X. 1939. Biological studies in Hawaiian water-loving insects, Part III: Diptera or flies, B: Asteiidae, Syrphidae and Dolichopodidae. Proceedings of the Hawaiian Entomological Society 10: 281-315.

Woodley, N.E. 1989. Phylogeny and classification of the ‘Orthorrhaphous’ Brachycera. Pp. 1371-1395 in McAlpine, J.F. and Wood, D.M. (eds.), Manual of Nearctic Diptera. Volume 3. Agriculture Canada Monograph 32, vi + 248 pp.

First published on the Internet on 18 November 2005
S.E. Brooks