One thousand three hundred and eighty-three valid species of Pipunculidae have been described and over 2,500 species likely exist (De Meyer, 1996; De Meyer and Skevington, 2000; Skevington unpublished database, 2005). Most big-headed flies that have been studied are endoparasitoids of leafhoppers and planthoppers, including Cicadellidae, Cercopidae, Delphacidae, Membracidae, Issidae, Cixiidae and Flatidae. The only exceptions to this rule occur in the genus Nephrocerus, flies that were recently discovered to attack Crane Flies (Tipulidae) (Skevington, 2005). The potential value of Pipunculidae for biological control has stimulated some work on the bionomics of this family. For example, recent research into the control of the potato leafhopper, Empoasca fabae (Harris), a major pest of alfalfa in mid-western and eastern United States and Canada, involved exploration within Europe for natural enemies to be introduced into the United States (Jervis, 1992) and included rearing of Chalarus for release (Skevington & Marshall, 1997). Current research in Texas is focusing on the discovery of pipunculid parasitoids in the pest leafhopper, Homalodisca coagulata Say (Glassy-winged Sharpshooter). Despite the economic importance of the group, few data on host relationships exist and some genera have no known hosts (for example Allomethus, Basileunculus, Elmohardyia, and Protonephrocerus).
Some of the recent Pipunculidae systematists: Top row left to right: Martin Dempewolf, Jeff Skevington, Mihaly Foldvari. Bottom row left to right: Michael Ackland, Marc De Meyer, Jose Rafael, Forbes Benton. International Congress of Dipterology, Oxford, 1998.
Adults are frequently seen hovering among vegetation; their flight is similar to that of Syrphidae. Adults utilize all terrestrial habitats; however, diversity and numbers are greatest in forest openings and along forest edges. Adult flies feed on honeydew and can occasionally be found in large, mixed feeding groups on Sternorrhyncha secretions (Skevington & Marshall, 1998). Many pipunculids employ the landmark mating system known as hilltopping (Skevington, 2000, 2001). Hilltop collecting is an excellent way to sample much of the pipunculid diversity in an area and often provides large numbers of specimens. Other effective methods frequently employed to capture pipunculids include sweeping, Malaise trapping, and less successfully, using yellow pan traps. Occasionally, mating pairs are discovered hovering in copula or temporarily settled on vegetation. Pronounced sexual dimorphism in pipunculids makes association of the sexes difficult so these occasional discoveries are very useful.
Females of most pipunculid species deposit their eggs in early instar nymphs or adults of their hosts. After visually locating a host, some species remove the host from the food plant and oviposit one egg inside each host whilst in flight (Huq, 1982; May, 1979; Williams, 1919), whereas others leave the host in situ (Benton, 1975). Larvae develop to maturity within the nymph or adult hosts. When mature, the larva leaves the host through a break in one of the dorsal intersegmental membranes of the abdomen in order to pupate in the soil, in the litter, at the base of plants or rarely, attached to leaves (Ferrar, 1987; Perkins, 1905). More detailed information on immature stages together with information on rearing techniques can be found in Benton (1975), Coe (1966), Ferrar (1987), Freytag (1988), Huq (1984), Jervis (1980), Morakote & Yano (1987) and Perkins (1906). Pipunculid-host associations are best known for the European fauna (Waloff & Jervis, 1987), followed by Nearctic Region (Skevington & Marshall, 1997) and the Australian region (Skevington, 2001). However, most species have no biological data available.
Most pipunculid species attack more than one species of host, but show a preference for a particular set of host species. Only two species have been reared from more than one subfamily of host (Skevington, 2001). Superparasitism and multiple parasitism are rare and survival of more than one pipunculid in these cases is exceptional (Jervis, 1980; Morakote & Yano, 1988; Waloff & Jervis, 1987).
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