Proctotrupidae

Description & Statistics

Masner (1993) noted that in this family the body was 3-10 mm long, somewhat robust, usually black and with predominantly smooth sculpture except on the propodeum. Mandibles are usually unidentate. Antennae are thread-like, with 11 flagellar segments in both sexes. The forewing has a distinct stigma, with relatively wide closed costal cell and closed radial cell formed by tubular veins, and with other veins nebulous. The transscutal suture (between the tegula) is absent. The metasoma in lateral view is somewhat curved, with its apex distinctly curved downward in females. Metasomal tergum 1 and sternum 1 are fused to form the petiole. The petiole is fused posteriorly with sternum 2 (the petiole sometimes is overlapped by the anterior margin of the syntergum). Terga 2-4 are fused into a syntergum. All terga in lateral view overlap the sterna considerably to entirely. The female ovipositor has heavily sclerotized sheaths.

Most species are solitary endoparasitoids of Coleoptera larvae that live in the soil litter and rotten wood. Some species parasitize larvae of Mycetophilidae (Diptera). Gregarious parasitism occurs and is considered a secondary adaptation. In all species a peculiar emergence pattern from the host occurs. The parasitoid larva pupates outside the host larva but remains connected by its posterior end to the ventral surface of the host, as in Pelecinidae. A thin membrane (but no cocoon) is formed on the parasitoid pupa. Adults are common in wet, shaded habitats. Males usually are found in Malaise traps, females in pan or pitfall traps.

Townes & Townes (1981) recognized three subfamilies: Vanhorniinae, Austroserphinae (= Acanthoserphinae) and Proctotrupinae. In this report Vanhorniinae is treated as a separate family.

Austroserphinae

With 3 genera and a few species in Australia, New Guinea and South America, represents an archaic group with the most complete wing venation, though most of the veins (M, Rs+M, Cu) are only nebulous. The scape has one or two sharp spikes. The mandibles are almost vestigial. Austroserphus has the ovipositor and sheaths enclosed in a long gutter-shaped extension of the apical sternum that seemingly is used for digging or for piercing during oviposition (Masner 1993).

Heloriserphus

With two species from Chile, represents in Masner's (1993) opinion, a separate subfamily characterized mainly by the unique structure of the metasoma, which is not curved downward at the apex, is campanulate rather than laterally compressed with the sterna considerably exposed, and has the ovipositor protruding straight backwards in line with the body's longitudinal axis.

Proctotrupinae

Is the largest subfamily, with 21 genera of very uniform appearance worldwide. There are 310 described species but as many as 1,200 have been estimated for the world fauna.

Townes & Townes (1981) revised the world species. Nixon (1938) keyed the British species. Pschorn-Walcher (1971) keyed the species of Switzerland, but the key can be used for all of central Europe. Kozlov (1987) keyed the species for the former USSR. Kozlov (1978/1987) noted that there were 12 genera in the Palearctic. They are parasitoids of larvae of beetles concealed in soil (Elateridae, Staphylinidae, Carabidae) and in fungi (Erotylidae, Nitidulidae, Phalacridae and Melandryidae), larvae of Diptera concealed in fungi (Mycetophilidae), and larvae of beetles of family Coccinellidae.

Immature Stages of Proctotrupidae

The information on the egg and the larval instars of the Proctotrupidae (noted as Serphidae by Clausen 1940) is incomplete. The egg of the species attacking Scymnus larvae in Japan (Fig. 29A) is somewhat cylindrical, but s1ightly wider at the anterior end; the poles are smoothly rounded; and it measures 0.2 mm. in length and 0.06 mm. in width. The ovarian egg of Paracodrus observed by Zolk is somewhat elongated and measures 0.14 to 0.16 mm. in length.

The first instar larva from Scymnus (Fig. 29B) is polypodeiform, and the large paired ventral processes occur on the first thoracic and the first four abdominal seg­ments. The head is large and heavily sclerotized, bears heavy falcate mandibles, and is thus quite similar to that of mandibulate type larvae. The body is widest at the juncture of the thorax and abdomen and narrows appreciably to the seventh segment, following which is the apparently four segmented tail, which is directed dorsad almost at right angles to the body axis. The integument bears no spines or setae and is much more delicate on the tail than on the remainder of the body. There is no evidence of a tracheal system or spiracles.

The larva of Phaenoserphus viator described by Eastham is similar to the above in the essential characters, except that 10 body segments are recognizable, of which the last is much the longest and in older specimens is seen to comprise 4 segments, making a total of 13. The fleshy paired ventral processes occur on the second and third tho­racic and the first six abdominal segments and are considered to be vestigial organs. The distal portion of the tail bears vertical fin‑like projections both dorsally and ventrally.

The following instars are of normal form, lacking the large head, the paired appendages, and the tail. The third instar of P. viator may be recognized by the presence of 8 pairs of nonfunctional spiracles, whereas the fourth instar has 10 pairs, situated on the second and third thoracic and the first eight abdominal segments. Both of these instars have the labrum projecting over the mouth in the form of a rounded beak. There are no integumentary spines or setae.

The mature larva of the Japanese species (Fig. 29C) is slender and cylindrical, with i3 body segments, of which the last is small and tapers to a point. The tracheal system has the same number and arrangement of spiracles as occurs in P. viator.

The pupae of all species that have been studied have the posterior portion of the abdomen strongly curved ventrally.

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Serphidae

These are either solitary or gregarious parasitoids of the larvae of Coleoptera (Staphylinidae, Carabidae, Coccinellidae and Elateridae). Some species are also known from Diptera. Serphus ater Nees was reared from the centipede, Lithobius sp. The value of serphids in biological control is suspect because of their attack on predaceous beetles; however, they are usually so scarce in collections, that not much attention has been focused on them as biocontrol agents.

Biology & Behavior

The life history of Phaenoserphus viator Hal., a gregarious internal parasitoid of carabid larvae in Europe, was studied by Eastham (1929). He presumed a single annual generation on Pterostichus niger Schall., and adults appear during August and September in the field. Larval development is slow during the periods that the host is feeding and hibernating, and 1st instar larvae persist until the host larva nears pupation in spring or early summer. Rapid parasitoid growth then ensues, and the host body contents are rather thoroughly consumed. After feeding, the larvae (30 or more) emerge from the body in an orderly manner. Just prior to breaking through the integument, they are all oriented longitudinally, with heads directed caudad. Individual ruptures in the integument are made in transverse rows of 3-4, always ventrally and intersegmentally. About 3/4ths of the parasitoid body is extruded from the wound, and the caudal portion remains within it to serve to hold the prepupa and pupa in position. Immediately after emergence, the last larval molt occurs, but no cocoon is formed. The external prepupal stage is 7-10 days and the pupal stage lasts ca. 2 weeks (Clausen 1940/1962).

Phaenoserphus viator, a parasitoid of the larvae of Carabus in Europe, was studied by Raynaud (1935). Behavior is similar to P. viator, except that winter was thought to be passed in the egg stage.

Paracodrus apterogynus Hal. is parasitic on the larva of Agriotes. Its development is similar to Phaenoserphus, and emergence habit is identical, although if the number is not excessive only two individuals emerge from each intersegmental area (Zolk 1924). A single host gives rise to 14-52 parasitoids, and gravid females may contain as many as 170 eggs.

Exallonyx philonthiphagus Williams is a solitary internal parasitoid of mature larvae of Philonthus turbidus Erich. in Hawaii. Fully fed larvae emerge from the host body through an aperture in the 5th or 6th abdominal segment ventrally (Williams 1932). The pupa lies with its venter to that of the host, and the head is pointed forward. In female pupae, only the tip of the abdomen remains within the host body, while in males the head and thorax only are external (Clausen 1940/1962).

In Japan observations have been made on an unnamed species which was solitary on Scymnus larvae (Clausen 1940/1962). Oviposition took place in 1st and early 2nd instar larvae and was accomplished by bringing the abdomen forward beneath the body and inserting it by a rapid thrust, somewhat ventrally, in the host's mid abdominal region. Larval development was rapid, and feeding was completed at the time the host larva attached itself to the leaf or bark in preparation for pupation. Then the parasitoid larva lay with its head at the caudal end of the body. The host body contents were not entirely consumed, and feeding was apparently only on the fluid or semifluid contents. Emergence from the host was not by cutting the integument, but in a manner as follows: The head of the mature larva was pressed against the skin ventrally near the caudal end of the body. Then, by rhythmic pulsations over several hours, it was forced outward slowly until a break occurred. When most of the body was free, the last larval exuviae was cast and the pupa then lay venter to venter with the host and with the tip of the abdomen curved ventrally, enveloped in the last larval exuviae, but still embedded in the host body. It required circa 12 hrs for complete emergence and another 36 hrs before pupation, the entire cycle being completed in circa 20 days (Clausen 1940/1962).

Clausen (1940) noted that it appears that there is considerable uniformity in the manner of larval development, emergence from the host body and the peculiar position assumed by the pupa beneath the host.

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Vanhorniidae

Description & Statistics

Masner (1993) noted that in this family the body is 6-7 mm long. The mandibles are exodont. Antennae are inserted just above the clypeus. The metasoma has most segments fused to form a large carapace. The ovipositor is housed in a ventral groove on the metasoma, with its apex projected forward.

Vanhornia eucnemidarum Crawford parasitizes larvae of Eucnemidae (Coleoptera) in old, dying maple trees (Acer spp.). The family has one genus with 5 species: one in Europe, 2 in North America (one undescribed), one in China and one in Japan (undescribed) (Masner 1993).

Mason (1983) described the structure of the metasoma. He & Chu (1990) described a species from China. Deyrup (1985) gave information about the biology of V. eucnemidarum.

The family was represented by a single North American genus and species, Vanhornia cucnemidarum Cwf. in 1940 ((Clausen 1940/1962). The parasitoid was reared from the cells of larvae of the coleopterous family Eucnemidae in decaying or sound wood (Crawford 1909). At that time no biological studies were made.