Checklist of UK Recorded Torymidae

Description & Statistics

Torymidae is a moderately sized family. The family currently includes 68 genera and 986 species placed in 2 subfamilies, Megastigminae (12 genera with 174 species) and Toryminae (55 genera with 808 species). In the past the family had been referred to as the Callimomidae.

Most Torymidae are solitary. Typically the British Torymids will use their long ovipostors to oviposit through plant tissue, usually into galls or developing seeds, but some oviposit into pupae concealed in silk or plant tissue. A few species parasitize larvae of Lepidoptera, some species are found in the cocoons of moths and puparia of flies, as well as insect eggs. Monodontomerinae parasitise the cocoons of Lepidoptera and Hymenoptera. Amoturoides was found to develop in a tachinid attacking polistine wasps. The Diomorus and Ecdamua species are associated with sphecid wasps in old burrows in dead wood and firm plant stems. Four genera of the Podagrionini are parasitic in mantid eggs, species of Rhynchoticida and Chrysochalcissa attack heteropterous eggs.

A number of species are associated with seeds and plant galls and are phytophagous. Phytophagous species include seed-eaters that feed on the highly nutritious endosperm in developing seeds. The majority of such species belong to the genus Megastigmus though other genii include (Bootania, Bootanellus both non UK genii) and Torymus. They develop in seeds of various Cupressaceae, Pinaceae and arborescent Rosaceae. The species which have been studied have similar biologies; the female oviposits in early summer into the developing seeds in the young cones or fruits and the solitary larvae feed all summer, consuming virtually the entire contents of the seed. They overwinter as prepupae in the seed, before generally pupating the following spring. Some individuals of certain species may diapause for two or three years. Most species are restricted to a single plant genus. For example, Megastigmus aculeatus develops in the seeds of roses, M. bipunctatus attacks those of juniper and M. spermatrophus feeds on Douglas Fir. This latter species occasionally assumes the status of a minor pest in Scotland where it has been found to damage seed stocks. Megastigmus suspectus is a pest of Abies alba in Europe. Amongst the Toryminae Torymus (Syntomaspis) species are known to feed in seeds of various arborescent Rosaceae such as Sorbus, Pyrus, Malus and Crataegus. The adult Megastigmus emerges through a small circular hole. A least 2 species of foreign Megastigmus develop in figs.

Xenostigmus species are recorded as gall-makers, though non are present in the UK. The rest are associated with plant galls. Many Torymid larvae may be entomophagous, primary, ectoparasitoids of gallicolous (gall-forming) cecidomyiid and cynipid larvae or, less commonly, phytophagous. Some may even be both, feeding in turn on gall maker and then on gall tissue when the gall making larva is consumed, eg Glyphomerus stigma. The majority develop in various galls and are usually regarded as parasitoids.

The majority of species of the subfamily Toryminae, many Monodontomerinae and a few species of Megastigminae are idiobiont ectoparasitoids of the inhabitants of plant galls. For example, Torymus erucarum, Megastigmus dorsalis and M. stigmatizans attack insect larvae found in cynipid galls on oaks, Glyphomerus stigma is a parasitoid in Diplolepis galls on rose, such as Diplolepis rosae and some North American species of the genera Pseudotorymus and Cryptopristus parasitize gall-forming eurytomids and cecidomyiids. Not all parasitic torymids attack the inhabitants of galls. One species of Torymus has been observed to be a hyperparasitoid developing ectophagously on a pteromalid parasitoid of beetle larvae in Sarothamnus seed-pods. This torymid was never found as a primary parasitoid of the beetle larva. Several torymids are associated with aculeate Hymenoptera. For example, one British species of Torymus, T. armatus is a parasitoid of stem-nesting sphecids, especially species of Rhopalum. The torymid oviposits through the plant-stem wall on to the aculeate prepupa in its cocoon. Another British species, Monodontomerus obscurus is an ectoparasitoid of various solitary bees, especially megachilines of the genera Osmia and Megachile as well as the Lepidoptera leaf miner Coleotechnites piceaella on Norway spruce (Kearfott, 1903).

Several species of Torymus that oviposit into cynipid galls do not develop as parasitoids instead they are inquilines and develop on the gall tissue competing with the actual gall-maker, either after having destroyed the cynipid (eg Torymus auratus), or alongside the cynipid larvae which is destroyed later (eg T. cyaneus).

One of the most complex of torymid life-histories is that of Monodontomerus aereus. This species is a gregarious internal parasitoid of various lymantriid pupae, but it may also develop as a hyperparasitoid. In such a case it feeds externally on the ichneumonoid or tachinid primary parasitoid, unless the tachinid puparium happens to be very fresh and then it will develop endophagously. Various other species of Monodontomerus are known to parasitize diprionids, heterarthrine tenthredinids and sphecids, and species in related but non-British genera attack scolytid, bruchid and curculionid beetles.

Important morphological characters include;
They are metallic green or bronze, sometimes yellow, except for the Megastigminae, which are primarily yellowish or brownish, though often with black markings, and have complete, well-formed, parapsidal sutures, and a forewing with setal tracts.
Medium-sized chalcids with a body generally elongate, excluding ovipositor about 1.1-7.5mm in length, averaging 5mm, including ovipositor up to 16.mm in length
Cercal plates not flat, slightly raised and papillar in form
The ovipositor is exserted, thread-like, and often several times longer than the body.
a 12-13 segmented antenna with 1-2 annuli present.
Hind coxae are 3X larger than fore coxae, more or less triquetrous and triangular in cross section rather than round. Hind tibiae straight.
Petiole strongly transverse, not distinct
Stigmal vein very short (although sometimes with stigma very enlarged) so that apex of uncus almost touches anterior margin of forewing
Pronotum more or less long, attenuated slightly in front, or rectangular.

The extent of this family has undergone several changes, especially since the description of some puzzling tropical forms. Earlier all chalcids with a long ovipositor were regarded as torymids but gradually it became evident that this character developed independently in several groups. More recently it was found that the true torymids have relatively long cerci (sometimes unnecessarily called 'pygostyles') and again some alien forms were misplaced in Torymidae, e.g. the pteromalid Roptrocerus Ratzeburg in the North American catalogues. For the same reason Ormyrus was removed from the family either to the pteromalids (Riek, 1970) or as a family of its own. The limits of the family can now be settled by the presence or absence of the horseshoe-like occipital carina. The presence of this character clearly separates the torymids from other forms having protruding ovipositors, especially from the fig wasps, Agaonidae, unusual Pteromalidae, and also from the Chalcididae. The separation of torymids from chalcidids seemed sometimes vague because of the enlarged and toothed hind femora in Podagrionini, but these parasites of mantids are clearly torymoid and differ from Chalcididae by the presence of the occipital carina, long ovipositor together with the short last two tergites and long cerci, and by the absence of the genotemporal carina. The occipital carina does occur in some other groups, e.g. in Tetracampidae and in several subfamilies of Pteromalidae (Diparinae, Spalangiinae, Cerocephalinae, Asaphinae), so it can be regarded as a symplesiomorphy. However, in the evolutionary line of torymids it seems to be in harmony with other characters, such as the shortened stigmal vein compared with the long marginal vein; the relatively large hind coxae and their attachment to the thorax; the mentioned terminal terga with cerci; the complete notauli; the undifferentiated clypeal area; the invariably 13-segmented antennae, etc., although the occipital carina may become obliterated in some extralimital genera (absent in the American Erimerus Crawford), notauli become very shallow in a few species, the marginal vein may become shortened (e.g. extralimital Liodontomerus Crawford and Chalcimerus Steffan & Andriescu). Notwithstanding this it seems reasonable to regard Torymidae as a monophyletic group as delimited here."

"The horseshoe-like occipital carina should not be confused with a secondary transverse fold of some pteromalids, e.g. Trichomalopsis Crawford, Dibrachys Förster. The mentioned terminal terga are abdominal terga IX and X, counted as gastral tergites 7 and 8, following the spiracle-beraring sixth tergite. In Torymidae the seventh tergite is dorsally extremely short but separated from the eighth tergite by a membranous line, on sides the membrane widens and bears the mobile elongate cercus with long sensorial setae. The eighth tergite is also short, flap-like, often only weakly sclerotised. it is followed by the membranous anus (faeces may be stuck there in some dead specimens) situated just above the base of the ovipositor and its sheaths. This arrangement is similar to some forms of Agaonidae, but in these (e.g. Apocrypta) the cerci are moved ventrad and are placed within the sclerotized side part of the seventh tergite, and the occipital carina is invariably absent, the marginal and stigmal veins are different, etc."

"Torymidae share one character with Agaonidae which seems to separate them both from Pteromalidae and from the groups regarded as possibly derived from the last family. In torymids and agaonids (as here defined) the back of the head has the postgenae expanded to the median line so that the hypostomal margins are medially strongly constricted or even fused some distance below foramen magnum... In pteromalids the hypostomal margins are generally almost straight from the mandibular base to the sides of the foramen.

Immature Stages of Torymidae

The normal egg form in the Torymidae is elongate-oval to kidney-shaped, with the anterior end broadest and terminating in a short, rounded protuberance (Clausen 1940, noted as Callimodidae). The posterior end is somewhat attenuated, and in occasional instances it terminates in a sharp point. The egg of Epimegastigmus brevivalvus described by Noble is markedly different, for it possesses a slender stalk about 2X the length of the egg body. The illustrations of eggs of this species in different stages of embryonic development show the had of the larva at the end of the egg opposite the stalk, and the latter must thus be posterior, as opposed to its anterior position in the normal stalked egg of the superfamily. In this species and in Callimome cyanimum, the chorion is unsculptured and glistening, while in Ditropinotus aureoviridis (Fig. 45A), Monodontomerus aereus, Eridontomerus isosomatis and Callimome abbreviatus it is densely clothed with minute papillae except, in some species, for a small area at the posterior end. These papillae often give the egg a grayish color.

The stalked type of egg described above for Epimegastigmus is of general occurrence among the phytophagous members of the family, although the stalk is normally at the anterior end.

The 1st instar larvae are hymenopteriform, with 13 distinct body segments, and bear rather large, cylindrical antennae and sensory setae on the head, heavy and long sensory setae on the body segments, particularly the thorax, which may equal the length of several segments, and spiracles on the 2nd thoracic and 1st 3 abdominal segments. Each body segment also bears a band of short integumentary setae.

Several species show departures in one or more characters from the above. The larva of Epimegastigmus brevivalvus is very stout, is devoid of sensory and integumentary setae, and has no spiracles or internal tracheal system. In D. aureoviridis, there are thought to be 5 pairs of spiracles, the additional pair being on the metathorax, and there are indications of this pair in Eridontomerus isosomatis, also.

Five larval instars have been observed and described in D. aureoviridis, E. isosomatis, M. aereus and Epimegastigmus brevivalvus. In the first two species, the 2nd instar larvae are readily distinguished from the first by the reduction in size of the sensory setae and the absence of the bands of integumentary setae. The sensory setae then become progressively larger and the integumentary setae more abundant in the following instars. The full complement of spiracles appears on the 2nd instar larva, situated on the last two thoracic and the first seven abdominal segments. In E. brevivalvus, the internal tracheal system is first evident in the 3rd instar, but open spiracles do not occur until the 5th.

The mature larva of most species bears heavy and long sensory setae and one or more rows of long integumentary setae in a band encircling each segment, giving it a distinctly hairy appearance. In D. aureoviridis (Fig. 45B) and Eridontomerus isosomatis, the head is also densely clothed with setae and spines of varying length. The larva of Epimegastigmus brevivalvus bears a closer resemblance to those of the phytophagous members of the family, the integument being smooth and shining except for a transverse row of very minute setae on each segment. That of P. pachymerum is distinguished by a heavy band of minute setae, set upon tubercles, on each segment.

In a considerable number of species, the mandibles of the 5th instar are simple, as are those of the earlier instars, but in E. brevivalvus they are tridentate, and in Megastigmus dorsalis F. and Epibootania nonvitta Gir. they are 4-dentate.