The pteromalids represent one of the largest "families" of the Chalcidoidea, consisting of about 2800 world species of morphologically and biologically diverse habits. In our view, this "family" is the most artificial of the Chalcidoidea. It seems to be defined primarily by what it does not have in relation to other families, and yet there are always exceptions. Thus, for example, it does not have the enlarged hindfemora of the Chalcididae (except Chalcedectini), it does not have the quadrate (rectangular) pronotum of the Eurytomidae (except Spalanginae), it does not have the exserted ovi-positor of the Torymidae (except for Cea and Roptrocerus), and so on.

As with any large group of taxa, especially a poorly defined one, the approach to classification differs widely from taxonomist to taxonomist. For example, Riek (1970) and Burks (1979) considered ormyrids a subfamily of Pteromalidae, whereas Graham (1969) considered them a distinct family. Riek also considered eucharitids a subfamily of Pteromalidae, but Burks and Graham considered them a distinct family. The details become extremely difficult to follow and are too cumbersome for a handbook such as this. What seems useful to us is to present a series of groupings which seem to represent natural ones (monophyletic lineages). Whether these are called families (as some have been) or subfamilies or tribes (as others have been) is largely irrelevant. What is important, is to realize that the groupings seem to be reasonable (morphologically and biologically). What they actually represent in terms of evolution and relationship to each other is speculative. The following scheme does not match the most recent edition of the Hymenoptera Catalog (Burks 1979). We have used the more recent classification of Boucek (1988) without attempt at explanation. This classification parallels more closely the one used in the generic keys to Nearctic Pteromalidae by Boucek and Heydon (in Gibson, et al. 1997).

From a practical point of view, identifying Pteromalidae is not easy. In the Nearctic Region the generic key by Boucek and Heydon (1997, in Gibson, et al.) provides the only starting place. Boucek alone (1993b) recognized over 40 genera new to the Nearctic Region. Additional keys to genera and species are listed below in appropriate places. Sometimes a host approach may work (e.g., a useful paper for identifying pteromalid parasitoids of Nearctic muscoid Diptera is that of Rueda and Axtell (1985) which includes over 150 SEM photos of the 10 most common pteromalids associated with these flies).

One of the most useful reference for pteromalid taxonomy in the Northern Hemisphere is Graham (1969). His work is a monument to the family and provides a basis for future work throughout the world. He treats over 800 species in about 200 genera for Northwestern Europe (British Isles and Scandinavia; but all European genera are included). More recently a key to West-Palearctic genera of pteromalids by Boucek and Rasplus (1991) has improved upon Graham, especially by the addition of hundreds of illustrations.

The best work for the Australasian area is Boucek (1988) who treats 28 subfamilies, 235 genera, and lists all of the species for the region. Keys to the 80 genera of India were published by Farooqui and Subba Rao (in Subba Rao and Hayat 1985). Yoshimoto and Ishii (1965) gave keys to 11 genera and 17 species of the family from Micronesia. The Neotropical Region is essentially untouched.

STATISTICS: Number of world species: about 3000 (about 350 Nearctic); number of world genera: about 550 (about 230 Nearctic).

BIOLOGY AND DISTINGUISHING CHARACTERS: In the subfamily sections which follow, biology and morphology are discussed by group rather than being given in a single source for the entire family. Comments given below concerning relative abundance and hosts are meant to help in confirming an identification based upon the key. The key attempts to cover all subfamilies of Pteromalidae, but some are so rare they will not likely be collected. Additionally there are a few genera which are not currently placed to subfamily and these are briefly mentioned at the end of the following list.

COMMONLY COLLECTED SUBFAMILIES

Spalangiinae: There are about 10 Nearctic species and about 25-50 world species in 2 genera. The genus Spalangia was revised by Boucek (1963) at the world level.

BIOLOGY: These wasps are associated almost exclusively with flies, especially those breeding in animal manures, carrion, and decaying plant tissue (Muscidae, Calliphoridae, Scarcophagidae, Drosophilidae, and Chloropidae). Eggs are laid through the puparial wall, externally on the dipterous body. The spalangid larva moves about on the host until it finds a suitable point of attachment where it begins feeding.

CHARACTERS: Black, ant-like wasps, dorso-ventrally compressed with forward projecting head and antennae attached at sides of mouth. The metasoma is petiolate, the thorax and head are usually covered with punctures, and the notauli are complete.

BIOLOGY: This group is poorly known biologically, but most seem to parasitize wood-boring beetles and a few parasitize stem or mud nesting Hymenoptera (e.g. Sphecidae, Megachilidae, Eumenidae).

CHARACTERS: In general, with the eyes diverging ventrally and the pronotum often relatively long (from anterior to posterior margin, generally as long as wide). Notauli may or may not be present. Some species have the hindfemur enlarged but without ventral denticles and the tibia straight, but the Chalcedectini have enlarged hindfemora with ventral denticles and an arched hindtibia (chalcidid-like). In some species the forefemur may be enlarged with 1 or more ventral denticles.

BIOLOGY: Most members are parasitic on Diptera, especially Agromyzidae, Cecidomyiidae, Tephritidae, and Anthomyiidae. A few species are reported from Lepidoptera, Coleoptera, and Hymenoptera (Cynipidae).

CHARACTERS: Distinguishing morphological characters are discussed under the next subfamily.

BIOLOGY: This group is largely reared from holometabolus insects including numerous Lepidoptera, Coleoptera (such as Chrysomelidae, Scolytidae, Curculionidae), Diptera (such as Cecidomyiidae, Chamaemyiidae, Syrphidae, Calliphoridae, and Muscidae), and Hymenoptera (such as Diprionidae, Ichneumonidae, and Braconidae). A number of species are hyperparasitic on other parasitic Hymenoptera (e.g. Aphelinus and Aphidiidae) through aphids. A few attack predaceous Diptera (Syrphidae, Chamaemyiidae) that attack Homoptera. One species of pteromaline, Dibrachys cavus, has been recorded from about 200 hosts in dozens of families across several orders.

CHARACTERS: In his discussions of Pteromalinae, Graham stated (1969:352) that he could not attempt to "... give a formal definition of the group." In general (i.e. many exceptions are present!), Pteromalinae have the notauli incomplete, the clypeus striate and its anterior margin more or less straight, 1 hindtibial spur, and a non-petiolate abdomen. Miscogasterinae generally have complete notauli, the clypeus smooth or reticulate and its anterior margin often with small teeth, 2 hindtibial spurs, and a petiolate abdomen.

BIOLOGY: The Nearctic species Eutrichosoma mirabilis is the only one with known hosts, namely Aleutes tenuipes (Leconte) and Smicronyx tychoides (Leconte) (Coleoptera: Curculionidae) (Boucek 1974b). This species may be extremely abundant in places, and thousands of specimens may be collected in a short period of time (e.g. we have taken them sweeping Parthenium infested with Smicronyx).

CHARACTERS: This subfamily is the only one that has the axillae advanced and almost meeting medially at the hind margins as well as the body covered with flat, scale-like setae.

BIOLOGY: The only hosts known are for the Nearctic species Elachertodomyiaphloeotribi (Ashmead), a parasite of twig-boring beetles, and for Colotrechnus ignotus Burks reared from heads of Asteraceae.

CHARACTERS: There are few genera or species, but the group is distinct based upon the forward projecting axillae, the stigmal vein which is as short as, or shorter than, the stigma itself, the postmarginal vein which is about as long as the stigmal vein (much as in the torymids), and the scutellum which has two submedian, parallel longitudinal grooves.

BIOLOGY: The species are parasites of Scolytidae and Curculionidae on coniferous trees (Graham 1969), and we have seen specimens reared from twigs of the evergreen broadleaf California-Bay (Umbellularia californica). Macromesus americanus Hedqvist is the only known Nearctic species of this group.

CHARACTERS: Females of this group are the only pteromalids to have the midtarsi 4-segmented (males are 5-segmented), and both males and females have 2 grooves on either side of the face below the eyes (i.e. apparently with 2 malar grooves; other pteromalids have 1 or none). The only known Nearctic macromesine appears to have a triangular projection at the apex of the scutellum.

BIOLOGY: All members, except one, parasitize wood-boring beetles and/or possibly their braconid parasites. The species Choetospila elegans Westwood is a cosmopolitan parasite of grain and stored-product beetles (e.g. cigarette beetle: Lasioderma serricorne (L.); drugstore beetle: Stegobium paniceum (L.); granary weevil: Sitophilus granarius (L.)).

CHARACTERS: Members of this subfamily have a globose head with a tooth-like ridge projecting from between the base of the antennae. The body is generally smooth and often yellow or brownish in color.

BIOLOGY: The biology of this group is unknown, but many species have been collected in leaf litter or duff by the use of Berlese funnels.

CHARACTERS: This group is usually distinguished in females by the strong, dark bristles that adorn the head and thorax (much as in many Diptera). In males, the antennal "segments" are usually very long, thin, and with erect setae. Many females are wingless and look considerably different than the males. Graham (1969) pointed out that in one species of Dipara the males and females have been put in different subfamilies. Wingless females may easily be mistaken for proctotrupoids, and one genus (Trimicrops) was originally placed in the Ceraphronidae (Graham 1969).

BIOLOGY: The known hosts for this group are European records of plant-mining Diptera (Agromyzidae, Drosophilidae, Graham 1969).

CHARACTERS: In addition to the extremely low antennal insertion mentioned in the key, ceines may be distinguished by the propodeal spiracles which are situated halfway between the front and hind margins of the propodeum. It is possible that an uncommon genus or species from two other subfamilies might key to this group based upon the low antennal placement: one is a genus of Asaphinae that can be separated by the carinate cheeks and occiput of the head, and the other is some members of the Eunotinae that may be told by the distinctly concave back of the head (see figure below). Both groups also have the propodeal spiracle closer to the anterior margin of the propodeum whereas in Ceinae it is midway between the front and hind margins.

COLLECTING: Darling and Hanson (1986) suggested that because Ceinae are associated with leaf litter a Berlese funnel is the best method of collection.

BIOLOGY: The subfamily is parasitic (or hyperparasitic through encyrtids) on scale insects (Coccidae: e.g. Saissetia, Ceroplastes, Lecanium, Eriopeltis) and mealybugs (Eriococcidae: Eriococcus). The European species Eunotus cretaceus Walker is known to be predaceous as a larva, eating the eggs of Eriopeltis (Graham 1969).

CHARACTERS: The head has a sharply defined occipital edge with the posterior ocelli touching it, and the first abdominal tergum is at least half as long as the entire abdomen.

BIOLOGY: Members of the genus Asaphes are hyperparasitic on aphidiid wasps in aphids. The genus Hyperimerus attacks parasites of pseudococcids and is also associated with Neuroptera (e.g., Chrysopa, Hemerobius), although exact host-parasite relationships are not known (Burks 1979). Bairamlia species in Europe are parasitic on Siphonaptera larvae (Graham 1969), one attacking fleas in squirrel nests and the other attacking fleas in bird nests. Hosts for the single Nearctic species of Bairamlia are unknown.

CHARACTERS: Members of this subfamily are most easily recognized by the well-developed genal (cheek) carinae that flank the sides of the head.

BIOLOGY: Although biology is unknown for the subfamily, it has been collected on dead or felled trees, and the long ovipositor is typical of wasps that parasitize wood-boring larvae (LaSalle and Stage 1985).

CHARACTERS: These are extremely unusual chalcidoids and could easily be mistaken for ichneumonids or braconids. The extra-Nearctic species are long (up to almost 4 cm including the well exserted ovipositor), but the Nearctic one is only 1 to 2 cm. All species are elongate and thin. In all species the head has well-developed ridges and crests in the area between the eye and antennal basin.

BIOLOGY: These small wasps are parasites of leaf-mining Diptera (Boucek 1988).

CHARACTERS: This subfamily is recognized by the dense setae that cover the head (including eyes), the dorsum of the mesosoma, and the wings. In addition, the first gastral tergum is half the length (or more) of the abdomen, and is polished dorsally.