Checklist of UK Recorded Diapriidae

Description & Statistics

This is a cosmopolitan family with medium sized parasitoids. Important morphological characters include antenna inserted on frontal prominence, 13-14 segmented in male, 12-15 segmented in female; head globose to subglobose; mesonotum without parapsidal sutures. The mandibles are bidentate; maxillary palps are 4-5 segmented; labial palps 2-segmented; gaster subpetiolate; middle and hind tibial spurs weakly developed.

Diapriids are primary, pupal endoparasitoids of Diptera. Some species are hyperparasitoids and some facultative hyperparasitoids. Both solitary and gregarious species are known. The family has not been used effectively in biological control.

Members of the family are internally parasitic on immature stages of Diptera. Species of Galesus and most Trichopria oviposit in dipterous puparia.

Galesus silvestrii Kieff. is parasitic in pupae of Tephritidae, and it was unsuccessfully attempted to introduce the species to Hawaii in 1913 for biological control. it develops readily as a secondary parasitoid also, through various Opius species (Pemberton & Willard 1918). During oviposition females stand on the puparium , with the body somewhat arched, and insert the ovipositor perpendicularly. Eggs are placed within the body of the pupa. It is subelliptical, has both ends smoothly rounded, with the chorion smooth, and is circa 0.36 mm long. When the host puparium already contains an Opius larva, the egg is placed within its body rathern than in the body of the fruit fly pupa. Such also occurs if Tetrastichus larvae are present, though these are very small, being only 2X the length of the Galesus egg. Maturity may be reached in these larvae, though the resulting adults are dwarfed (circa 1.5 mm. long).

The 1st instar larva is robust and mandibulate. The head is very large, somewhat flattened and heavily sclerotized, beraring a pair of very large curved mandibles. There are 12 body segments, the last one bearing a pair of terminal lobes which carry a number of setae. There are no additional integumentary spines or setae. Second instar larvae lack the large, heavily sclerotized head of the 1st instars and is normal inform. Neither this nor the 1st instar possess a tracheal system. The supposed 3rd and final instar larva is elongate, with 12 body segments, and its distinguishing feature is the possession of a complete tracheal system with three pairs of large spiracles on the thoracic segments (Clausen 1940/62). The contents of the host puparium are entirely consumed. The meconium is cast by the prepupa, and after the final molt the pupa lies with its head at the anterior end of the puparium. On account of this, empty puparia which have yielded Galesus are not easily distinguished from those which have produced flies.

Adults do not fly very much and spend most of their lives on or in the soil in search of host puparia. The cycle from egg to adult is completed in 25-32 days. There is no thelytoky known.

Trichopria hirticollis Ashm. is a gregarious internal parasitoid of Sarcophaga and other blowfly pupae (Roberts 1935). The lfie cycle takes 25-30 days. Diapria conica F. develops similarly in the puparia of the syrphid Eristalis tenax L. (Sanders 1911). Young puparia are preferred and the ovipositor is usually inserted just behind the pupal cornicles. The ovipositor remains inserted for 1-3 hrs, and the full complement of mature eggs is deposited on the one host. An average of 35 individuals develops in each puparium. There is a preponderance of females, but no thelytoky is known.

Trichopria stratiomyia Kieff (Cros 1935), which attacks Stratiomyia anubis Wied. in Algeria, shows different behavior by attacking larvae rather than puparia. The ovipositor is inserted by a backward thrust through the thin intersegmental membrane. Death of the host occurs without before pupation, and a maximum of 293 individuals has been reared from a single host. Mating occurs outside the host body just after emergence.

Various species of Trichopria are important in the natural control of synanthropic Diptera, such as house fly, Musca domestica L. Phaenopria occidentalis has been imported to California from the West Indies for biological control of chloropid eye gnats of the genus Hippelates (Legner & Bay 1964, 1965; Legner & Olton 1968, Legner et al. 1966a,b, 1967)

Masner (1993) noted that in this family the body was mostly 2-4 mm long, and rarely as small as 1 mm or as large as 8 mm. It is smooth and highly polished. The antennae are somewhat distinctly elbowed, with moderately to strongly elongated scapes inserted high above the clypeus, usually as a prominent transverse ledge. The forewing lacks a stigma but sometimes has a slightly thickened marginal vein. The metasoma is distinctly petiolate with a true or apparent tergum 2, which is the longest. The ovipositor is almost entirely retracted.

Endoparasitism of various Diptera (larval-pupal, or pupal parasitoids) seems to be a basic mode of development, but some other orders are parasitized by the more advanced groups. Adults are usually found in damp, shaded habitats such as in forests and marshes, near or in water, and in the soil. Four subfamilies are recognized: Belytinae, Ismarinae, Ambositrinae and Diapriinae. These apparently form natural units that are well characterized both morphologically and biologically. The family has about 150 genera and circa 2,300 described species. The fauna is estimated to include 4,;500 species worldwide. In North America there are circa 300 species (circa 200 in Canada). Most noneuropean taxa are undescribed.

The subfamilies are further discussed by Masner (1993) as follows:

Belytinae

is thought to be the most primitive subfamily on the basis of morphology and hosts. The forewing has relatively complete venation, usually with 3 closed cells (costal, medial, and radial), and metasomal tergum 2 is formed by 1 large tergum. Belytinae is best defined by a single synapomorphy: 2 longitudinal grooves on metasomal sternum 2 in which the lateral margins of tergum 2 fit. This groove may continue on the following sterna, sometimes supplemented by a ridge. The antenna of Belytinae usually has 13 flagellar segments in females (rarely 12 or only 10), 12 in males, with flagellomere 1 sexually modified. The scape is relatively long, inserted high on the frons on a distinct ledge. Although there are few reliable host records, Belytinae appears to be confined to Mycetophilidae and Sciaridae (Diptera) (Chambers 1971). The subfamily occurs worldwide mostly in moist habitats, with the greatest diversity and abundance in the cool southern temperate forests of Chile, New Zealand, Tasmania and southeastern Australia.

Ismarinae

is probably the most aberrant subfamily, both morphologically and biologically. The female antenna has 13 flagellar segments, the male has 12. Segment 2 is sexually modified. The scape is relatively short, about 2.5X as long as wide, inserted rather low on the frons, which is not expanded into a ledge. The mesosoma is relatively short and highly convex dorsally, with notauli reduced to small anterolateral depressions. The metatibia is strongly incrassate. Metasomal segment 1 is a very short petiole, the rest of the metasoma being campanulate, with the terga fused to various degrees to form a carapace. In the most primitive species all the sutures between terga are superficially indicated, giving a large single tergum 2, but in more advanced species the sutures gradually become evanescent until only one suture remains between tergum 7 and 8. The unique position of Ismarinae, not only within Diapriidae but Proctotrupoidea in general, is emphasized by its biology. Adults are hyperparasitoids of Cicadellidae (Homoptera) through larvae of Dryinidae (Chambers 1955, Waloff 1975, Jervis 1979). With only a few rare or infrequent species in one genus this relict subfamily is the smallest in Diapriidae.

Ambositrinae

has the ancestral number of flagellar segments as in the previous two subfamilies (females 13, males 12). Male flagellar segment 2 is usually sexually modified. The metasomal sternum 2 is divided by a deep suture from the large sternum 3, and the metasomal tergites are sharply margined laterally and acutely flexed under to couple with the sterna. In most genera the large tergum 2 (syntergum) is composed of fused terga 2, 3, and 4 so that the metasoma has only 5 visible tergites in females and 6 in males (2 primitive Southern Hemisphere genera have one extra free tergum visible). The wing venation is relatively reduced, with the radial cell not closed, the marginal vein usually very short, and the costal vein sometimes absent (e.g., Ambositra). The sexes are occasionally markedly dimorphic, with females brachypterous or apterous, almost ant-like, the males macropterous. On occasion both sexes are brachypterous. Their biology is known from only one species. Hosts are assumed to be Mycetophilidae and related Nematocera (Diptera). There are circa 20 genera, mostly with Gondwanan distribution. Most species occur in moist forest habitats in south temperate zones (Masner 1993).

Diapriinae

has the derived number of flagellar segments either 11 in both sexes or 10 in females and 12 in males. Numerous variations occur, resulting in a reduced number. The male antenna is thread-like, often with long hairs or bristles, and segment 2 is modified. The female flagellum is somewhat distinctly clavate or incrassate near the apex. The forewing has reduced venation. In some species the wing appears to be or really is veinless, and the radial cell is not closed. Primitive Diapriinae (Psilini) have a true large tergum 2, but in most derived members (Spilomicrini, Diapriini) the apparent tergum 2 is actually composed of terga 2 and 3 fused into a syntergum. Hosts are primarily Diptera Orthorrhapha (Tabanidae, Stratiomyidae, Syrphidae) and Cyclorrhapha (e.g., Muscidae, Anthomyiidae, Tachinidae, Calliphoridae, Sarcophagidae, Chloropidae, Tephritidae). Secondarily, some species changed hosts to Coleoptera (Staphylinidae, Psephenidae), and some seem to parasitize larvae of Formicidae. Some species occur in extreme habitats, where their hosts are found, e.g., the intertidal zone of continents and subantarctic islands (Early 1978, 1980), deep in the soil, in mammal burrows, and in bird nests. Species of several highly specialized genera of Diapriini are highly integrated with army ants in the New World and termites (Dictuoptera: Termitodea) in the Old World tropics. Huggert & Masner (1983) assumed that some of these species changed hosts gradually from parasitizing scavenging Diptera living in ant nests to ants themselves. But, only two records are available to support this (Huggert & Masner 1983, Loiácono 1987).

Kieffer's (1916) key to world genera is largely of historical value. Keys by Nixon (1957, 1980) for Britain (also good for northwestern Europe), and Kozlov (1987) for the former USSR are acceptable for beginners. There are no modern keys to world genera. Masner (1976) revised the New World Ismarinae. Masner (1961) proposed the subfamily Ambositrinae. Naumann (1982, 1987, 1988) revised the Ambositrinae of Australia, New Zealand, New Guinea, and Oceania. Hellén (1963) keyed the Finnish Diapriinae.

Kozlov (1978/1987) described this family, as translated from the Russian, "Body predominantly oblong, head small, antennae long, and wings long and broad. Flight poor (sluggish fliers). Sometimes wings reduced or entirely absent. Body usually smooth and lustrous, dark. Abdominal petiole narrow, differing markedly from other segments of abdomen."

"Endoparasitoids of puparia and larvae of flies. Only species of the genus Ismarus parasitize cysts of dryinid wasps. Various diapriids are commonly found in large numbers in humid habitats, especially in broad-leaved forests, in glades, and in meadows."
"Diapriids have not been studied well in the Soviet Union and thus their species composition is not fully known."

Immature Stages of Diapriidae

Detailed information on immature stages of Diapriidae is being acquired. However, Clausen (1940) noted that the 1st instar larva (Fig. 35A) is robust in form and of the mandibulate type. The head is very large, a bit flattened, and heavily sclerotized. It bears a pair of very large curved mandibles. There are 12 body segments; the last segment bears a pair of terminal lobes that have a number of setae. Otherwise there are no integumentary spines or setae.

The 2nd instar larva (Fig. 35B) lacks the large, heavily sclerotized head of the preceding instar and is of normal form. Neither this nor the 1st instar possesses a tracheal system. The supposed 3rd and final instar larva is elongated, with 12 body segments, and possesses a complete tracheal system with 3 pairs of large spiracles on the thoracic segments. The contents of the host puparium are entirely consumed. The meconium is case by the prepupa, and after the final molt the pupa lies with its head at the anterior end of the puparium.