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HYMENOPTERA, Diapriidae (Proctotrupoidea) --  <Images> & <Juveniles>



Description & Statistics


          Diapriidae. -- Diapriids are small to tiny black insects, most of which are parasites of immature Diptera. The form of the head distinguishes them; the antennae arise on a shelf like projection in about the middle of the face.   Their length ranges from 2-8 mm.  Most species are parasitoids on the larvae and pupae of a many kinds of insects, particularly Diptera, and  few are hyperparasitoids that parasitize Dryinidae, which attack leafhoppers. There are about 2310 described species in 152 genera..


          This cosmopolitan group shows considerable diversity of form with aptery being common.  There is sexual dimorphism with males and females frequently being mistaken for separate species. Winged forms have a reduced venation, with the greatest reduction in the subfamilies Ambositrinae and Diapriinae.


        These insects occur near the ground in wooded areas, for they attack fungus gnats (MycetophIlidae) and other flies breeding in fungi.  Some species have been introduced into California for the biological control of Hippelates eye gnats.


        This is a cosmopolitan family whose diagnostic characters include an antenna inserted on a frontal prominence, 13-14 segmented in male, 12-15 segmented in female; head globose to subglobose; mesonotum without parapsidal sutures.  The mandibles are bidentated; 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, while other species are hyperparasitoids and some facultative hyperparasitoids.  Both solitary and gregarious species occur.  The family has not been used effectively in biological pest control. Some are internally parasitic on immature stages of Diptera.  Species of Galesus and most Trichopria oviposit in dipterous puparia.


        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 that carry a number of setae.  There are no additional integument 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 possesses 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 that 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) [also please see section of Biological Control of Medical & Veterinary Pests <bc-37.htm>].


        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 the more advanced groups parasitize some other orders.  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 ca. 2,300 described species.  The fauna is estimated to include 4,;500 species worldwide.  In North America there are ca. 300 species (ca. 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 ca. 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 the genera is of historical value.


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  References:   Please refer to  <biology.ref.htm>, [Additional references may be found at: MELVYL Library ]


Ghesquière, J.  1944.  Rev. Zool. Bot. Afr. 34:  353-62.


Kozlov, M. A.  1978/1987.  Family Diapriidae (Diapriids).  In:  G. S. Medvedev (ed.) 1987, Keys to the Insects of the European Part of the USSR. Vol. 3 Hymenoptera, Pt. 2.  Akad. Nauk., Zool. Inst., Leningrad, SSSR. (trans. fr. Russian, Amerind. Publ. Co., Pvt. Ltd., New Delhi).  1341 p.


Legner, E. F. & E. C. Bay.  1964.  Natural exposure of Hippelates eye gnats to field parasitization and the discovery of one pupal and two larval parasites.  Ann. Ent. Soc. Amer. 57:  767-69.


Legner, E. F. & E. C. Bay.  1965.  Culture of Hippelates pusio (Diptera: Chloropidae) in the West Indies for natural enemy exploration and some notes on behavior and distribution.  Ann. Entomol. Soc. Amer. 58(4):  436-440.


Legner, E. F. & G. S. Olton.  1968.  Activity of parasites from Diptera: Musca domestica, Stomoxys calcitrans, and species of Fannia, Muscina and Ophyra  II.  at sites in the Eastern Hemisphere and Pacific area.  Ann. Ent. Soc. Amer. 61: 1306-14.


Legner, E. F., E. C. Bay & T. H. Farr. 1966a. Parasitic and predacious agents affecting the Hippelates pusio complex in Jamaica and Trinidad.  Canad. Entomol. 98(1):  28-33.


Legner, E. F., E. C. Bay & R. A. Medved.  1966b.  Behavior of three native pupal parasites of Hippelates collusor in controlled systems.  Ann. Entomol. Soc. Amer. 59(5):  977-984.


Legner, E. F., E. C. Bay & E. B. White.  1967.  Activity of parasites from Diptera:  Musca domestica, Stomoxys calcitrans, Fannia canicularis and F. femoralis, at sites in the Western Hemisphere.  Ann. Entomol. Soc. Amer. 60(2):  462-468.


Masner, L.  1961.  Inst. Sci. Madagascar Mem. 12:  289-92.


Pemberton, C. E. & H. F. Willard.  1918.  J. Agr. Res. 15:  419-65.