Proctotrupoidea

Description & Statistics

All species are parasitoids that attack immature stages of other insects. Most are small or minute and black, and may often be confused with cynipids, chalcidoids or some aculeates. The smaller species have a much reduced wing venation, but they may be distinguished from chalcidoids by the structure of the mesosoma and ovipositor. The pronotum in the proctotrupoids seems triangular when viewed laterally and it extends to the tegulae. The ovipositor originates from the tip of the metasoma rather than from anterior to the tip.

Families recognized are Calliceratidae, Diapriidae, Heloridae, Mesoserphidae, Monoserphidae, Pelecinidae, Platygastridae, Proctotrupidae, Roproniidae, Scelionidae, Serphidae, Trupochalcididae and Vanhorniidae.

Masner (1993) included 9 families in this superfamily: Austroniidae, Diapriidae, Heloridae, Monomachidae, Pelecinidae, Peradeniidae, Proctotrupidae, Roproniidae and Vanhorniidae. Only two of the included families, Diapriidae and Proctotrupidae, have many species. Omitted were families Calliceratidae, Mesoserphidae, Monoserphidae, Platygastridae and Scelionidae which are included in this report. Masner (1993) considered a separate superfamily Platygastroidea in which he placed the Scelionidae and Platygastridae. The entire superfamily seems to be very old, with some intermediate groups missing, so that existing families are isolated from one another and can be easily distinguished.

This superfamily is difficult to define morphologically because of its taxonomic diversity. Nevertheless, all species are strongly sclerotized and nonmetallic. The antennae have a constant number of flagellar segments (at both specific and generic levels), and do not possess longitudinal placoid sensilla. The metasomal segment 2 (obvious or true) is frequently the largest segment. The ovipositor is either internal or external, and is housed in heavily sclerotized sheathes (in Vanhornia it is in a ventral groove on the metasoma). it always issues from the metasomal apex (Masner 1993).

The biology and hosts are diverse. Most species are predominantly parasitoids of various Coleoptera, rarely Symphyta or Neuroptera. Diapriidae and Monomachidae seem to be confined mostly to Diptera, although several species of the former parasitize Coleoptera or Formicidae, and Ismarus is hyperparasitic on Homoptera through Dryinidae (Masner 1993).

There are circa 2,500 described species, but worldwide there are estimated to be 6,000 species. Two groups seem to form more natural units: Pelecinidae, Vanhorniidae, Proctotrupidae, Heloridae, Peradeniidae and Roproniidae in one group, and Monomachidae, Austroniidae and Diapriidae in the other.

Kozlov (1978/1987) discussing the superfamily Proctotrupoidea, stated, as translated from the Russian, "The following families of parasitic hymenopterans are included in the superfamily Proctotrupoidea: Mesoserphidae, Trupochalcididae, Heloridae, Roproniidae, Proctotrupidae, Vanhorniidae, Monomachidae, Diapriidae, Scelionidae, Serphitidae and Platygastridae. The first two families have been described only on the basis of fossil forms. Heloridae, Proctotrupidae, Diapriidae, Scelionidae, Serphitidae and Platygastridae are found in the European part of the USSR. The family Roproniidae is distributed in the eastern Palearctic and Nearctic. Vanhorniidae in the Nearctic, and Monomachidae in the Australian zoogeographic region."

"The average size of Proctotrupoids varies as follows: Heloridae and Proctotrupidae - 5.0 mm, Diapriidae - 3.5 mm, Scelionidae and Serphitidae - 1.5 mm, and Platygastridae - 1.0 mm. Baeus seminulum from the family Scelionidae, with a body length of about 0.20 mm, is one of the most minute chalcids, while some fossil forms of proctotrupoids reached a length of 14 mm, excluding the protruding parts of the genitalia."

"The antennae of proctotrupoids may be divided into two major types. The length of the first, or basal antennal segment in the first type is about 1.5 times greater than the width of this segment. In Europe, such antennae are typical of members of Heloridae and Proctotrupidae. The length of the first antennal segment in the second type is at least 3.0 times (usually more than 3.0 times) greater than the maximum width of this segment. Such antennae are found in Diapriidae, Scelionidae, Serphitidae and Platygastridae. Furthermore, the antennae of males and females of Heloridae and Proctotrupidae are equal in length, while in the other families listed above they usually differ in females from males in number of segments or in being clavate."

"One of the major characters distinguishing proctotrupoids from other superfamilies of parasitic hymenopterans is venation of the forewings. In Recent forms the most complete venation and maintenance of location of the veins are seen in members of the families Heloridae and Proctotrupidae. Venation of the forewings in specialized forms of proctotrupoids (Diapriidae, Scelionidae, Serphitidae, Platygastridae) is characterized by notable reduction and fusion of individual veins and properties of convergent similarity with other chalcids. In such cases, unlike other chalcids, the pronotum in proctotrupoids extends along the sides of the tegulae. In the keys and descriptions of these families veins in the forewings have been designated as follows: costal, subcostal, basal, marginal, postmarginal, stigmal, or radial and cubital."

"Short-winged and apterous forms are rather common among proctotrupoids. Wing reduction in Proctotrupoidea is probably related to their adaptation to unique and limited ecological conditions of existence. Wing reduction is evident in these three groups: (1) species associated with the soil (usually only females apterous; the search for hosts on the soil surface in wood and dry plant residue, often penetrating slits, cracks, insect pathways, and burrows of rodents; in males the wings are not reduced since they do not search for hosts in such conditions); (2) in myrmecophils (inhabitants of ant hills); and (3) in Mantibaria manticida from the family Scelionidae; adults are ectoparasites of the praying mantis and live under its wings."

"The segment connecting the abdomen with the thorax is treated as the first, although morphologically it is the second, and often labeled the abdominal petiole. The fusion of several segments is often evident in the abdomen. For example, in Heloridae the tergite treated as the 2nd in the descriptions and keys was formed through the fusion of the 3rd to 5th tergites, and the sternite treated as the 2nd formed through the fusion of the 3rd to 6th sternites. In Proctotrupidae the segment treated as the 2nd tergite formed through the fusion of the 2nd to 4th tergites, and the 2nd sternite through the fusion of the 2nd to 5th sternites. Sclerites which have formed through the fusion of several tergites or sternites are treated as a single element in the keys."

The male genitalia of Heloridae and Proctotrupidae and the terminology of their structure are given... The male genitalia in these families are not flattened dorsoventrally, and the lappets of the edeagus and the digital sclerites, viewed ventrally, are vertical in position.... The male genitalia of Scelionidae and Platygastridae are highly modified; the paramere, volcellar plate, and edeagus have fused and form a cylinder. Furthermore, dorsoventral flattening of the male genitalia is evident in the last two families, and the plates of the edeagus have opened in this process, while the digital sclerites have assumed a horizontal position."

"Recent proctotrupoids are characterized by endoparasitism: their larvae develop as endoparasites of various arthropods, usually insects. Each family is associated with a definite and typical host range. Species of the monotypic family Heloridae have adapted to larvae of the family Chrysopidae. Species of Proctotrupidae parasitize the larvae of beetles living in soil (Carabidae, Elateridae and Staphylinidae) and in fungi (Erotylidae, Nitidulidae, Melandryidae), larvae of some flies living in fungi, and larvae of phytophagous ladybirds of the family Coccinellidae. Synchronization of cycles of development of the host and parasite, and gregarious and solitary parasitism are also characteristic of Proctotrupidae. members of Diapriidae are endoparasites of the pupae and larvae of flies of the families Agromyzidae, Bibionidae, Calliphoridae, Chloropidae, Muscidae, Sarcophagidae, Stratiomyiidae, Syrphidae, Tabanidae and Tachinidae. Reports of members of Diapriidae being recovered from the pine moth and bark beetle are rather doubtful and require confirmation. Probably in these cases members of Diapriidae were secondary parasites. All species of the large family Scelionidae are endoparasites of eggs of arthropods, predominantly insects. Members of Platygastridae are mainly egg-larval and larval parasites of gall midges. Some groups of this family are parasites of coccids, whiteflies, and parasitic hymenopterans."

"One of the characteristic biological peculiarities of Platygastridae is polyembryony-- the development of several embryos in a single egg. The gradual establishment of polyembryony is evident here. The following types of embryogenesis have been recorded in Platygastridae: (1) Monoembryonic development-- one embryo develops from a single egg as, for example, in Platygaster herrickii and Synopeas rhanis; (2) Incidental polyembryony-- on the average, 3.0% of the eggs of Allotropa burelli contain two embryos; (3) Facultative polyembryony-- twin females develop from fertilized eggs of Platygaster hiemalis, and single males from unfertilized eggs; (4) Habitual polyembryony-- variable number of individuals develop from a single egg, e.g., 2 in Platygaster variabilis, 8 in P. vernalis, 10 to 12 in P. zosinae, and 11 to 18 in P. felti."

"Proctotrupoids are usually mesophilous and hygrophilous."

"Based on the morphological characters of the wings and antennae the families of the superfamily Proctotrupoidea can be divided into two major groups which represent two major phylogenetic branches or two major lines of evolution: (a) the helorid group (Mesoserphidae, Trupochalcididae, Heloridae, Roproniidae, vanhorniidae and Proctotrupidae); and (b) the diaprid group (Monomachidae, Diapriidae, Serphitidae, Scelionidae and Platygastridae). The first group is characterized by the following combination of characters: presence of anal lappet in hind wings; length of 1st antennal segment about 1.5 times greater than maximum width; and antennae of females and males unbranched and with the same number of segments. The second group is characterized by the following combination of characters: absence of anal lappet in hind wings; length of 1st antennal segment at least 3.0 times (usually more than 3.0 times) greater than maximum width; females usually differ from males in number of antennal segments or antennae of females clavate, and those of males filamentous."

"Recent members of Heloridae exhibit the largest number of ancient and primary properties in these two groups of families, but none of these forms can be considered an ancestor. Probably, the ancestor of proctotrupoids was some extinct form of Mesoserphidae (this family is known from the Middle Jurassic)."

"About 5,000 species from 590 genera of proctotrupoids are known in world fauna. The key includes 750 species of Proctotrupoidea from 6 families and 126 genera."