Biology & Ecology
Larvae. As far as is known there are five larval stadia, the last of which either pupates or goes into diapause. Therevids are usually univoltine, but instances where two or more years are needed to complete the life cycle are known in European Thereva species (Lyneborg 1992). The larvae are smooth and vermiform, with a rather well developed head with an apically spatulate tentorial rod (Irwin & Lyneborg 1981a, Irwin & Lyneborg 1981b). The abdomen is secondarily divided into some 16 apparent segments, and terminates in a pair of tiny pseudopods (Woodley 1989). The snake-like larvae are very mobile and move with considerable speed through sand and loose soil (Lyneborg 1992). They are found mainly in sand or soil close to the surface (English 1950). Therevid larvae are voracious predators, feeding on a great variety of insect larvae and earthworms, but preferring Coleoptera larvae. At least one New Zealand species has developed a cleptoparasitoid way of life (Lyneborg 1992). In captivity, therevid larvae can be fed on larvae of flour beetles, but should be separated as they can be cannibalistic.
Pupae. In the prepupal stage the larva assumes a curved position in the soil, somewhat like the letter U, or almost in a circle (Lyneborg 1992). The pupal stage lasts for only a week or two. The pupa is especially vulnerable to desiccation and to attack by predators (Lyneborg 1992).
Adults. In contrast to much of the world's therevid fauna, many species of Australian Therevidae are brightly coloured, elongate flies with largely glabrous bodies. Bright colouration, long antennae, body shape, together with behavioural modification, often results in wasp mimics, particularly in genera such as Agapophytus and Ectinorhynchus (Power 1998, Winterton & Irwin 2001). Many genera have attractively patterned wings and males with distinctive silvery pruinescent markings on the body. Many species show marked sexual dimorphism. The antennae are sometimes very distinctive, such as the greatly elongate scape in Agapophytus and the thickened scape in Neodialineura.
Field work in Australia continues to regularly uncover specimens of undescribed species.
Little is known of the food habits of Australian therevids, but adult therevids appear to feed on honeydew, flower nectar and pollen. Many taxa inhabiting subtropical regions with winter rain (i.e. parts of California, the Mediterranean area, southwestern Africa, and probably also south-western Australia) often have an elongated, projecting proboscis, and are recorded as visiting flowers, taking nourishment in the form of nectar (Lyneborg 1992). Several genera were collected in numbers from flowers of Baeckea and Nuytsia floribunda in spring in south-western Western Australia (Lambkin pers. obs). Therevids need to regularly drink water, and can often be found at drying pools and springs. Adult therevids often alight in sunny patches on trails and paths, or rest on sand, rock, leaves, stems, and tree trunks. They have a rapid flight of short duration. The flying period for some of the more common species is usually 3-4 months (Lyneborg 1992). In semi-arid and arid environments, therevids are stongly attracted to water. Pools of water in drying creek beds often attract a tremendous diversity of these flies. Many of the field photos included in this key were taken along the edges of such pools.
Lek formation on the trunks
of large, smooth-barked trees has been observed in the males of some species
of Agapophytus. At various sites in south-eastern Queensland, males
were observed forming small oval-shaped leks of up to eight individuals
on the shaded side of the tree approximately 12 metres above the
ground. Periodically, most members of the lek take-off and fly in a tight
loop perpendicular to the trunk and land again in approximately the same
position within the lek. Mating was observed on two occasions and took
place on the other side of the same tree or on a nearby tree. Males of
second species were observed forming slightly smaller sized leks on the
sunlit side of a tree approximately 0.5 metres above the ground (Winterton
& Irwin 2001).
One of the most intensive quantitative surveys of Therevidae was conducted in Australia in 1997-1998. A long-term Malaise trapping study near Brisbane was completed by Narelle Power as part of her Honours thesis at the University of Queensland. Narelle trapped therevid specimens using eleven 6 metre Focks Malaise traps based in three diverse habitats: coastal heath on Bribie Island, sclerophyll forest in Brisbane Forest Park, and rainforest at Mt Glorious. The weekly collections revealed a very diverse fauna of Therevidae in southeast Queensland. Over 1,000 Therevidae belonging to 15 genera and 52 species were collected over a 54 week period (Power 1998).
Individual abundance varied across the three sites with 47.5% of specimens collected from sclerophyll forest, coastal heath accounted for 39.2% of the total therevids, and the rainforest site just 13.3%. Individual species appear to be spatially restricted, with site species diversity related to the heterogeneity of the environment (Power, 1998). The majority of therevid species were represented by few individuals, with ten represented by less than 3 individuals. The results of an analysis of seasonal abundance were significant, finding that most specimens and all species were taken in spring (September-November) (Power 1998). Cooler southern areas of Australia may reflect the seasonal abundance in New Zealand, where three species of adult therevids have been collected during September, 16 during October, 30 during November, 36 during December, 37 during January, 30 during February, 13 during March, and 3 during April (Lyneborg, 1992). A similar situation was found in the genus Agapophytus, with the majority of collection records in Australia and New Guinea between November and February (Winterton & Irwin 2001). An American study of the bioecology of therevids (Hartman et al. 1995) in Sand Ridge State Forest in Mason County, Illinois, showed no obvious correlation between any of the six therevid species collected and microhabitat. Females were much less abundantly collected and were present about a week after the males first appeared. Three species had single population peaks as would be expected of univoltine species and two species peaked twice. All species were present in the first population peak, which occurred in late May to early June. The two most numerous species then peaked again in late July and early August, suggesting a second generation. Therevids have typically been thought to produce a single generation per year but data such as these suggest that some species are bivoltine. Similarly, a study by Mike Irwin along the Kuiseb River, Gobabeb, Namibia suggested that adults of some therevid genera may have a second generation.
Therevids as Bioindicators
English K. (1950). Notes on the morphology and biology of Anabarrhynchus fasciatus Macq. and other Australian Therevidae. Proceedings of the Linnean Society of NSW 75, 345-359.
Hartman M., Irwin M.E. and Kampmeier G.E. (1995) Habitat partitioning by therevids at Sand Ridge State Forest. January Report. Illinois Natural History Survey, Champaign-Urbana.
Irwin M. (1976). Morphology of the terminalia and known ovipositing behaviour of female Therevidae (Diptera: Asiloidea), with an account of correlated adaptations and comments on phylogenetic relationships. Annals of the Natal Museum 22, 913-935.
Irwin M. and Lyneborg L. (1981a). The genera of Nearctic Therevidae. Bulletin of the Illinois Natural History Survey 32, 193-277.
Irwin M.E. and Lyneborg L. (1981b) Therevidae. Manual of Nearctic Diptera. (ed. by B.V.P. J.F. McAlpine, G.E. Shewell, H.J. Teskey, J.R. Vockeroth & D.M. Wood) 1, pp. 513-523. Research Branch, Agriculture Canada Monograph, Ottawa.
Lyneborg L. (1992) Therevidae
(Insecta: Diptera). Fauna of New Zealand/ Ko te Aitanga Pepeke o Aotearoa
24, pp. 139. DSIR Plant Protection/ Te Wahanga Manaaki Tupu, Auckland.
Power N. (1998) Temporal and
spatial diversity of Therevidae in South East Queensland (Diptera: Therevidae).
Honours thesis, University of Queensland.
Winterton S.L. and Irwin M.E.
(2001). Phylogenetic revision of Agapophytus Guérin (Diptera:
Therevidae: Agapophytinae). Invertebrate Taxonomy 15, 467-526.
Winterton S.L., Irwin M.E.
and Yeates D.K. (1999). Phylogenetic revision of the Taenogera
Kröber genus-group (Diptera: Therevidae) with descriptions of two
new genera. Australian Journal of Entomology 38, 274-290.
Woodley N. (1989) Phylogeny and classification of the "Orthorrhaphous" Brachycera. Manual of Nearctic Diptera. (ed. by J. McAlpine, Wood, DM) 3, pp. 1371-1395. Research Branch Agriculture Monograph No. 32. Canadian Government Publishing Centre, Hull.