FNZ 24 - Therevidae (Insecta: Diptera) - Biology
Lyneborg, L 1992. Therevidae (Insecta: Diptera). Fauna of New Zealand 24, 140 pages.
(
ISSN 0111-5383 (print),
;
no.
24.
ISBN 0-477-02632-X (print),
).
Published 04 Mar 1992
ZooBank: http://zoobank.org/References/7D4AAC2F-32F3-4A36-883F-38834FFD9B3E
Biology
The follow ing notes contain some general information and are based only partly on New Zealand material.
Immature stages
The egg is 0.4-0.8 mm long, ovoid milky white, and without reticulation. The number of eggs laid by each individual seems to vary from about twenty five to about a hundred.
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, and this may also hold good for some New Zealand species. The snake-like larvae are very mobile and move with considerable speed through sand and loose soil. Therevid larvae are voracious predators, feeding on a great variety of insect larvae and earthworms, but preferring Coleoptera larvae. They are cannibalistic, at least when held in captivity. At least one New Zealand species, A. harrisi n.sp., has developed a cleptoparasitoid way of life. In the prepupal stage the larva assumes a curved position in the soil, somewhat like the letter U, or almost in a circle.
The pupal stage lasts for only a week or two. The pupa is especially vulnerable to desiccation and to attack by predators.
Adults: habitats
Information on the habitat preferences of New Zealand therevids is very scanty. A large proportion of the Anabarhynchus species and all Megathereva seem to be associated with coastal scrub and sandy beaches, habitats that are extensively exploited by therevids all over the world. A considerable number of species have been found on inland lake shores and in river beds. Many of the larger and darker Anabarhynchus species are probably associated with swampy open mountainsides and tussock country in hilly and mountainous regions. Anabarhynchus species can even be found in wet Nothofagus rain forest.A. harrisi occurs on former glacial plains of the Mackenzie district (see Remarks, p. 40).
Habits
Adult therevids are seemingly all diurnal; however, there are several records of New Zealand Anabarhynchus being collected at light during the night. Nothing is known of the food habits of any New Zealand therevids, but therevids seem not to be predaceous, and most species probably imbibe only some water and honeydew. Many taxa inhabiting subtropical regions with winter rain (i.e., parts of California, the Mediterranean area, southwestern Africa, and probably also southwestern Australia) often have an elongated, projecting proboscis, and are recorded as visiting flowers, taking nourishment in the form of ncctar.
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. Males of some species form hovering swarms. The female enters a swarm and is caught by a male, and copulation takes place.
To my knowledge the coupling has never been described in any therevid. A coupled pair of Ectinorhynchus cupreus is at hand from Trio Island, Cook Strait (Fig. 13). Segment 8 of the male is rotated about 90 degrees to the left (anti-clockwise), and the genitalia are rotated an additional 45 degrees to the left, resulting in 135 degrees of anti-clockwise rotation of the genitalia. There is no apparent vertical grasping effect of the male complex, i.e., of the epandrium against the gonocoxites.
The female S8 is inserted into the male genital complex with its exposed surface placed under the epandrium, intimately facing the ventral epandrial sclerite (= S10+11). The aedeagus and the adjoining, very elongate inner styles (= gonostyles) are inserted into the female genital chamber, which is demarcated dorsally by the furca and ventrally by S8. The aedeagus and inner styles reach about halfway to the anterior margin of the furca, and the inner styles are held approximated to the aedeagus, guided by a pair of grooves in the female S8. The very reduced outer styles have no obvious function, neither for grasping nor for anchoring.
Oviposition behaviour has been described by Irwin (1976). Judged from the morphology of the female genitalia, all New Zealand therevids belong to the group in which the female abdomen is embedded in the substrate by thrusting and contorting it until a major part is buried. As soon as the egg is laid, the abdomen is withdrawn.
Phenology (Text-fig. 2)
In New Zealand, adult therevids have been collected from September to April. Three species have been collected during September, sixteen during October, thirty during November, thirty-six during December, thirty-seven during January, thirty during February, thirteen during March, and three during April. The flying period for some of the more common species is usually 3-4 months.