Chalcidoidae | birkin-wildlife

Chalcidoidea

Chalcidoids are found in all zoogeographic regions and in all terrestrial habitats from equatorial forests to the northernmost tundra, from deserts to ponds, except for oceanic islands and islands separated from the "continental mass." (Gibson 1993). Although they occur almost everywhere, and the great abundance of numbers and species of chalcidoids, the taxonomy is poorly known. They are one of the poorest known groups of parasitic Hymenoptera, in part because of their small size (most are 3-5 mm or less in length. The smallest of them, the egg parasite Alaptur magnanimus Annecke, is one of the smallest insects, with a body length of about 0.2 mm.), morphological and biological diversity, and numerical abundance. About 3,300 nominal genera and 22,500 nominal species have been described, of which circa 2,000 genera and 18,500 species are considered valid (Noyes 1990a). The chalcidoids now equal the number of described species of Ichneumonidae. The number of species certainly represents only a fraction of the true diversity, and estimates of 60,000-100,000 chalcidoid species do not seem unreasonable (Noyes 1978, Gordh 1979).

The superfamily Chalcidoidea, commonly called chalcids or chalcid flies, is a large group of mostly small parasitic or phytophagous insects within the suborder Apocrita of the Hymenoptera. It is an economically important group of insects, because most of the larvae eat insects, thus helping to control or suppress insect pest populations on forest and agricultural crops. Included among its different families probably a majority of all entomophagous insects, and their range in form, habits, host preferences, and host relationships is extremely wide. Most species of chalcidoids are entomophagous in habit, parasitoids or, rarely, predators of the immature stages or, very rarely, of adults of 12 orders of Insecta, 2 orders of Arachnida (Araneae and Acari), and one family of Nematoda (Anguinidae). This represents about the same number of orders that are parasitized by the rest of the parasitic Hymenoptera combined. Few chalcidoids are phytophagous, either as gall formers or seed eaters, or as inquilines within the galls of other species and are distributed in a number of families. The plant-feeding habit in the superfamily has been reviewed by Gahan (1922) and the species listed which develop in that way. The Agaontidae comprise the fig insects, and the members of the subfamily Idarninae of the Callimomidae are associated with them in an uncertain capacity. Numerous other Callimomidae are seed feeders, as are also many Eurytomidae. The latter family also includes a considerable number of species that form plant galls, and a few species of Eulophidae and a single one of the Encyrtidae are stated to be of similar habit. It is generally accepted that the phytophagous habit is the more primitive in the superfamily and that the parasitic relationship is of more recent origin.

The superfamily, Chalcidoidea in Britain, consists of the following families:

Aphelinidae
Chalcididae
Elasmidae
Encyrtidae
Eucharitidae
Eulophidae
Eupelmidae
Eurytomidae
Mymaridae
Ormyridae
Perilampidae
Pteromalidae
Signiphoridae
Tetracampidae
Torymidae
Trichogrammatidae

Gibson (1993) included 29 families in Chalcidoidea: Agaonidae, Aphelinidae, Chalcididae, Elasmidae, Encyrtidae, Eucharitidae, Eulophidae, Eupelmidae, Eurytomidae, Leucospidae,

Mymaridae, Ormyridae, Perilampidae, Pteromalidae, Rotoitidae, Signiphoridae, Tanaostigmatidae, Tetracampidae, Torymidae and

Trichogrammatidae. He distinguished the fully winged chalcidoids from most other Hymenoptera by their reduced forewing venation. At most a single vein complex occurs, composed of the submarginal, marginal, stigmal, and postmarginal veins. Most chalcidoids also have a separate sclerite, the prepectus, partly separating the mesopleuron from a somewhat saddle-like or horseshoe-like pronotum. This is unlike most other parasitic Hymenoptera, which lack an exposed prepectus between the mesopleuron and pronotum, and have the pronotum highly reduced medially so as to be triangular in lateral view. Because a prepectus is present between the pronotum and the mesopleuron in most chalcidoids, the pronotum typically does not extend to the tegula, but how conspicuous this feature is depends on size of the prepectus (Gibson 1993). The position of the mesothoracic spiracle, if visible, also distinguishes chalcidoids from other parasitic Hymenoptera. In chalcidoids the mesothoracic spiracle is at the dorsal margin of the pronotum, usually at the juncture of the pronotum, prepectus, and mesoscutum, but at least between the pronotum and mesoscutum. Other parasitic Hymenoptera have the mesothoracic spiracle located below the dorsal margin of the pronotum, either between the pronotum and the mesopleuron (in some taxa concealed beneath a prominent pronotal lobe) or on the pronotum itself in this same relative position. Thus, the spiracle and mesoscutum are separated by the posterodorsal angle of the pronotum. Almost all chalcidoids also have longitudinal, ridge-like sensory structures (multiporous plate sensilla) on one or more flagellar segments, with the apices of the sensilla projecting above the surface, and often beyond the apex of the segments. Many also have a metallic sheen, which distinguishes them from most other parasitic microhymenoptera. Bou…ek (1988a) gave a comprehensive review of chalcidoid structure.

Feeding habits

As adults by and large they are poor flyers and generally confined to their host habitats. Adult chalcids sometimes live a short time (e.g. some Eucharitidae) and do not take any food, but most species, at least the females, live for weeks or months and then have to take at least some water. They either feed on the nectar of flowers or sweet secretions of suctorial insects such as coccids, aphids, and psyllids and consequently visit plants with aphid colonies. The females of many species get proteins by 'host-feeding,' ie. they lick oozing body fluid called the hemolymph, after piercing the skin of the host. This sometimes happens after oviposition but often the parasite makes a wound solely in order to obtain these nutrients and does not lay an egg in the host. The host insect may die from the infection in the wound, or even from loss of the body fluid. If the host so attacked is in a shelter, e.g. within a cocoon, a tube is constructed by a secretion coming from the ovipositor, as described and figured by Fulton (1933) for Pteromalus cerealellae (see also Clausen, 1940b: 123). The population of pest species may be strongly reduced by host-feeding of the parasites.

Parasitoids (Entomophagous Chalcids).

Most chalcids develop by feeding on other insects, rarely on some other arthropods (spiders, mites), and are called entomophagous. They are regarded as parasites in the broad sense, but because in general only the larval stages of chalcids feed this way, they are called either protelean parasites (e.g. Askew, 1971) or parasitoids. A parasite is understood to develop on one individual of its host, in distinction from a predator which consumes more individuals (called prey). The difference between the two is sometimes not easy to define. A larva of certain Eupelmus species attacking pockets of cicadid eggs embedded in plant tissue, may devour one or several eggs to complete development. On the contrary, if the host is much larger than the parasite, several eggs may be laid and the chalcid parasite is gregarious instead of solitary (if one parasite develops on one host). Some pupal parasites are gregarious. A special case of gregarious parasites are the polyembryonic encyrtids of several genera related to Copidosoma Ratzeburg. The early stages of the embryo separate into several to many clusters of cells most of which grow up into normal larvae, so that a single laid egg of the parasite gives rise to many individuals of the species.

"In all probability, the majority of species in the Chalcidoidea are primary parasites, and the known members of the Mymaridae, Trichogrammatidae, Leucospidae and Eucharidae are exclusively so. Other families have a varying proportion that act as hyperparasites, and some species develop indiscriminantly in both roles."

The insect hosts of the parasitic and predaceous members of the superfamily are extremely varied and represent practically all the more common orders, of which the preferred ones are the Lepidoptera, Diptera, Coleoptera, and Homoptera. These groups comprise the bulk of our major crop pests, and their chalcidoid parasites often serve to keep them in check. In biological control work, a considerable number of species have been imported into the different countries and have been successful in reducing the population of the pest species to a noneconomic level.

"The host rage of a species of chalcidoid varies from a single host species to a large number of species. Hence we may refer to monophagy (a parasite that lives on one host species), oligophagy (a parasite that lives on different species of the same genus), or polyphagy (a parasite that lives on species which belong to different but related families (Bendel-Janssen 1977)."

"When the primary parasite becomes parasitized by another parasite, the condition is known as secondary parasitism, or hyperparasitism. The secondary parasitism may develop into tertiary parasitism, which, in turn, may develop into quarternary parasitism. The primary, secondary, or tertiary parasite, which may itself become a host, may either live in its primary, secondary, or tertiary host at the time it becomes parasitized or it may already have left the host for its own further development (Bendel-Janssen 1977)."

The female searches for the host insect by the use of her olfactory, optical, and tactile senses. Chalcidoids are holometabolous. They develop through egg, larval, pupal, and adult stages. The egg is laid either outside or inside the host with the use of the ovipositor, which may be narrow and long as in the Torymidae or short and stubby as in the Eulophidae. Either the egg or the newly hatched larva may be deposited. The position and age of the host are important factors in the choice of host."

The host stages attacked are principally the egg and larva, though a smaller number develop in the pupa, and some of those attacking Homoptera may develop in the adults, also.

Parasitism is categorised on the basis of where the egg is laid and how the larva feeds. Most species attack the host directly, and the egg is either laid on the host and the larva develops externally (ectoparasitism), or deposited internally and the larva develops inside the host (endoparasitism), and both habits are commonly found within a single genus.

Well known exceptions are found in Perilampinae and Eucharitidae. Their eggs are laid mostly far from the actual host and the first-instar larva is of the planidium-type; it has no legs but the side margins of the tergites are produced ventrally and enable the larva to move. In many perilampids the planidium actively searches for the host and then attaches itself on it (e.g. Monacon) or bores into it and there waits till a primary endoparasite (braconid, ichneumonid or tachinid) eventually attacks the same host. The perilampid then gets into the body of the larva of this primary parasite (some Perilampus). In eucharitids the eggs are laid on leaves or in buds of plants in large numbers, because many larvae do not reach a suitable host. This is always an ant species. The planidium attaches itself on an ant which carries it into the nest and there the larva has to find an ant larva, but delays feeding till the host reaches sufficient size.

The attacked host is often immediately prevented from further growth and feeding, but in other cases the parasitic chalcid larva coexists with the feeding host for a considerable time. First Haselbarth (1979), and then Askew & Shaw (1986) have drawn attention to this important difference. Haselbarth termed the former parasites 'idiophytic' and the latter 'koinophytic,' whilst Askew & Shaw called them, perhaps more conveniently, idiobionts and koinobionts. The idiobionts include particularly the parasitic species attacking non-feeding stages of hosts, such as eggs and pupae, and they terminate the life of the host before it reaches the feeding stage. Host larvae and adults subjected to permanent paralysis by the attack of a parasite are also victims of the idiobiont strategy. On the other hand koinobionts are in particular larval and egg-larval parasite, less often among those attacking adult hosts. The koinobiont larva feeds first slowly on the host, allowing it to grow (and continue to be injurious to its host-plant, though the host's food consumption is often reduced). Its host may reach the stage of a mature larva or prepupa or even pupa, though often of reduced growth, before the parasite kills it.

Certain families are sharply restricted in their choice of host groups or host stages. Thus the Mymaridae and Trichogrammatidae develop exclusively in the eggs of various orders, the larvae that feed upon eggs are usually parasitic internally, but some may be true predators.

Practical entomologists are well acquainted with the egg parasites of the genus Trichogramma, which are used in the biological control of Lepidoptera pests; this genus belongs to the widespread, but poorly studied, family Trichogrammatidae, which comprises very minute egg parasites.

Larvae of the family Mymaridae also develop exclusively in the eggs of insects, but the inclusion of this family in the superfamily Chalcidoidea is still a controversial issue.

Some mymarids and trichogrammatids are capable of diving into the water, search for hosts which are invariably aquatic insects and parasitize them.

The Eucharidae occur only upon the larvae and pupae of ants (e.g., family Eulophidae). The female eucharid and perilampid deposit the first-instar larva (planidium) directly onto the vegetation where the larva searches for hosts. In the eucharids, the planidium attaches itself to an ant worker and is carried into the nest. The eucharids are parasites only of larvae and pupae of ants.

The great majority of Aphelinidae are parasitic on the nymphs of Homoptera, principally the Coccidae, Aphididae and Aleyrodidae.

Like encyrtids, members of the family Aphelinidae are also common parasites of coccids (and aphids); nevertheless this family is not related to encyrtids but to eulophids; the similarity in body dimensions of encyrtids and aphelinids is convergent.

The number of species of the family Encyrtidae also increases southward. Encyrtids constitute a highly specialized family, primarily associated with suctorial insects, mainly coccids. In northern regions encyrtids prefer dry habitats (slopes with a southern exposure, sand, and limestone deposits).

Some encyrtids are known to attack ticks and also eggs of spiders.

The families Pteromalidae and Eulophidae predominate in the European part of the USSR, and are primarily parasites of flies, Lepidoptera, and beetles, and even secondary parasites.

The Eulophidae are largely governed by the host habitat, and they attack larvae of leaf-mining Coleoptera, Diptera and Lepidoptera. that form leaf mines or that bore in stems.

The parasitic Callimomidae attack mainly the immature stages of gall-making Cecidomyiidae and Cynipoidea;

The family Chalcididae is rarely seen in the northern regions of the European part of the USSR, but quite common in the south. Chalcidids are larger, with highly thickened hind femora, and mainly primary and secondary parasites of Lepidoptera and flies.

The family Eupelmidae is quite unique in that these species arch their body upward and forward; eupelmids are also common in the southern European part of the USSR."

Others feed on plant tissues of stems, leaves, seeds, or flowers, or stimulate the host plant to develop abnormal vegetative growths, called galls.

Phythphagous Chalcids.

Phytophagy is found in Eurytomidae, Torymidae, Agaonidae, Pteromalidae, Tanaostigmatidae and Eulophidae (e.g. Gahan 1922a; now rather out of date). it appears in a number of groups, some of which seem to be rather old, primitive and therefore in them phytophagy may be the primary way of life. Eurytomidae, however, the Rileyinae, perhaps the oldest group, seem to include only entomophagous species and the phytophagous ones are found only in the more derived Eurytominae. Certain genera are wholly phytophagous (e.g. Tetramesa), others only partly so (e.g. Eurytoma). In the latter genus several species are known to develop as parasites on the phytophagous larvae of Tetramesa and at least in one case it was proved that if a young host larva is attacked, it is soon consumed and the 'entomophagous' Eurytoma larva then turns to the surrounding plant tissue (in a grass stem) and completes its development as a 'phytophagous' one. This suggests a secondary phytophagy. The explanation seems easy but a generalisation should be made with some caution. it seems, that the feeding habit of Tetramesa and of many other groups, is primarily phytophagous.

The association of chalcid with plant galls is generally widespread. Some species are known and others are suspected to be gall-makers. Tetramesa for instance is a cosmopolitan genus causing swelling, shortening and other deformations of grass stems, but the genus is relatively poorly represented in the region. A number of forms are associated with galls on eucalypts and acacias. The eulophids of the genus Ophelimus (earlier Rhicnopeltella) are suspected causers of small globular galls on leaves and other fresh growths on eucalypt species introduced from Australia to New Zealand, because no other insects were reared from the galls (Valentine, 1970; Somerfield, 1976). Species of another eulophid genus, Quadrastichodella, cause small seed-like galls in eucalypt flowers and these galls may then be introduced, mixed with seeds, to various countries, despite quarantine measures (Flock, 1957; Bou…ek, 1977b).

A number of pteromalids are gall-causers, especially the Ormocerinae. One of them, the bud-galling Trichilogaster acaciaelongifoliae, was recently introduced in the Cape Province of South Africa and proved very efficient in control of the earlier introduced Acacia longifolia growing as a weed. The galling of the acacia buds is so massive that it prevents the plant from producing any seed. Another gall-producing pteromalid is the peculiar, Austrosystasis developing in 'bullet-galls' on Eleocarpus. Many other Ormocerinae and Coelocybinae probably are phytophagous inquilines in the galls, as shown for Coelocyba aurocincta by Noble (1941).

Eurytomids are parasites of the most varied insects, especially those inhabiting stems and galls of plants; many eurytomids are secondary phytophages.

In some chalcidoids such as those of the family Eurytomidae, the larva feeds on plant tissues and it is frequently associated with galls on foliage and stems of many kinds of plants.

The population strength and species variability of the family Eurytomidae increase in a southerly direction.

The Torymids attack primarily the larvae in cecidomyiid and cynipid galls; others are secondary parasites on lepidopterous cocoons or dipterous puparia, and a few are phytophagous, the members of the genus Megastigmus feed on plant seeds.

The subfamily Toryminae is richly represented in the forest zone and Monodontomerinae in the steppes and deserts.

The torymids of the genus Xenostigmus gall buds of Hakea. Also tanaostigmatids, or at least some of them, are generally gall-causers, although there is so far no reliable regional evidence, apart from a rather confusing statement about Tanaostigmodes velasquezi (Girault, 1933 ).

Another group of phytophagous species are the seed-eaters (some Eurytomidae, Torymidae and Eulophidae). They feed on the rich seed tissues but do not produce a noticeable deformation. The above-mentioned genus Eurytoma also includes seed-eaters, but most species of that genus are clearly entomophagous and so far these habits have been found to bear little relationship to the taxonomy of the genus, except perhaps at the species-group level. It seems that in some other eurytomids the seed-eating habit is more consistently associated with the generic classification, especially in Bruchophagus, Systole and allied forms. Systole, as understood here, is confined to seeds of Cruciferae (Daucaceae), but Bruchophagus includes not only species feeding in seeds of Papilionaceae (Viciaceae) (including clover and lucerne) but also causing galls or developing in galls on various other plants, (e.g. Bruchophagus fellis and B. muli on Citrus). In other groups the torymids classified in Bootania are seed-eaters in Pandanus, some of those of Bootanelleus in Casuarina, some pteromalids of the genus Systasis develop in grass-seeds, etc.

All Agaonidae are phytophages and develop in the influorescences of the genus Ficus.

Another well known example is the pollinating fig-wasps, Agaoninae. Apart from the pollination by the adult, which is regarded as a high specialisation, the fig-wasp larva causes excessive growth of the ovarium of the fig flower and is actually a gall-causer. Gall-producing chalcids are found amongst Eurytomidae, Agaonidae, Pteromalidae, Tanaostigmatidae and Eulophidae. Some other species use the gall tissue as food bud do not cause galls themselves. These are the inquilines; they often co-exist with the gall-causers but in the past they were often labelled as 'parasites,' although probably most of them develop solely on plant tissues. Some of them, as recently discovered about Epichrysomalinae and Otitesellinae (of fig wasps), gall the female florets of figs as do the pollinating Agaoninae.

Reproduction

Reproduction of chalcids is mostly bisexual and, as generally in Hymenoptera, the males are haploid, i.e. have only half of the chromosomes of females which are diploid. Normally the fertilised egg produces a female and the unfertilised egg a male (arrhenotoky). The sperm is kept in a spermatheca and the female can lay either unfertilised or fertilised eggs, as is well known in the honeybee. In parasitic species the males are usually smaller than females and can develop on a smaller host. The pteromalid Lariophagus distinguendus lays unfertilised male eggs onto a small larva of the granary weevil, Sitophilus granarius, and female eggs (fertilised) on larger older larvae of the host (Assem & al., 1984). In some species parthenogenetic reproduction, i.e without mating, is widespread and mostly females are produced (thelytoky). Sometimes populations introduced outside the area of their original distribution consist only of females. For instance Macroneura vesicularis in New Zealand and North America is thelytokous and found only as females, whilst in Europe both sexes readily occur; hence Europe is regarded as the country of origin of the species." [this is not a valid criterion for judging point of origin, given that bacterial infection is now known to cause thelytoky].

This is not true for all strains of a species. In gregarious species, where many individuals emerge in a sheltered situation, as for example in a fig syconium (many fig-wasps) or in cells of large hosts under bark or a cavity in wood (Melittobia) or some other restricted niche (Nasonia), the males may be brachypterous or wingless and mate with their sisters. The latter are fully winged and disperse after mating in search for hosts. In most species males search for females, then sometimes the females may be shortwinged but the males are always fully winged. brachyptery and especially aptery (complete absence of wings) are always associated with great differences between the wingless sex and the winged one, in an evident dimorphism. Such extreme dimorphism is found in some Pteromalidae (e.g. Diparinae), most Agaonidae, many Eupelmidae, and Encyrtidae, but rather rarely in other families, and no brachypterous or apterous forms are known in Chalcididae, Leucospidae, Torymidae, Perilampidae, Eucharitidae, Signiphoridae and Tetracampidae. In some Agaonidae (e.g. Camarothorax) the females may be macropterous and the males are apterous or brachypterous (trimorphism). Otherwise sexual dimorphism is commonplace, exhibited at least in the form of the gastral apex and the antennae; there are very few exceptions to this, e.g. some Euplectrus (Eulophidae).

As normal in Hymenoptera, the chalcid pupa has free limbs (pupa libera), but in Entedoninae (Eulophidae) the pupal surface is fused as in pupa obtecta (as in Lepidoptera).

Before pupating the chalcid larvae do not spin any cocoon, except for a loose cocoon prepared by the gregariously ectoparasitic larvae of Euplectrini (Eulophidae). Another exception is the pteromalid genus Systasis (see Askew, 1971: 140).

"Many modifications in form are found among the eggs and the larval instars of the Chalcidoidea, a majority of which are definitely adaptive in character. Certain of these are common to whole families, whereas others appear apparently independently in widely separated genera and families. Under these circumstances, they cannot be considered to have a phylogenetic significance and are of limited usefulness in determining the taxonomic position of stages not associated with the adult insects. The first comprehensive study of the early stages of the Chalcidoidea, in which an effort was made to arrange the different groups in accordance with their taxonomic position, was that of H. L. Parker (1924)."

"In the aphelinids, the development of the male and female in the reproductive phase is expressed by the following terminology. The situation in which females develop as primary parasites and males as secondary parasites on their own larval female is known as autoparasitism. When males develop as hyperparasites on females of their own species, this is known as obligate adelphoparasitism, and when males develop on females of different species, this is known as facultative adelphoparasitism. When the female maintains the direct, indirect, or primary relationship and the male becomes a secondary parasite on the female larva or pupa of the same species, this is known as obligate autoparasitism. Much of the reproductive behavior is dependent on the mated or unmated condition of the female (DeBach 1964)."

"In the family Encyrtidae and in some species of Eulophidae, parthenogenesis is common. There are three types of parthenogenesis in chalcidoids, namely, arrhenotoky, deuterotoky, and thelytoky. Most species of parasitic Hymenoptera exhibit facultative parthenogenesis. The eggs may develop either parthenogenetically or zygogenetically, depending on the occurrence of fertilization. In the case of fertilized eggs (zygote), they are diploid and give rise to females, whereas unfertilized eggs (azygote) are haploid and give rise to males. This type of parthenogenesis is known as arrhenotoky. If the unfertilized eggs develop into both sexes (uniparental), this is known as deuterotoky. In obligatory parthenogenesis, each generation consists almost entirely of females, and this phenomenon is known as thelytoky (DeBach 1964)."

Polyembryony, a phenomenon in which several to several hundred or even thousands of imagines emerge from a singe egg, is met with in several genera of the family Encyrtidae."

Biology

"The larvae of chalcidoids are minute, often only 0.2-0.5 mm long. The greatest variation in larval form occurs in the first-instar larva with 14 types (Clausen 1940; Hagen in DeBach 1964: 179). The development thereafter (3-5 instars), tends to change to the usual hymenopterous type with a full complement of 10 spiracles, 12 or 13 visible segments, the greatest body width in the region of the thorax and first abdominal segment, and the lack of sculpturing, or segmented, processes on the first abdominal segment."

On anatomy, Yoshimoto (1984) employed the terminology of Graham 91959, 1969) and Richards (1956), and included reference to Hedqvist (1963), Snodgrass (1910, 1935) and Matsuda (1965, 1970).

Yoshimoto (1984) described the various structures as follows:

Head.-- "The compound eyes, which generally occupy the greater part of the side of the head, are the most obvious landmark. The ocelli, typically three, lie at the top of the head between the eyes in a more or less triangular arrangement. The central ocellus is the anterior (median) ocellus, and the outer ocelli are the posterior (lateral) ocelli. The distance between the posterior ocellus and eye margin is the ocellar-ocular line (OOL), and the distance between the posterior ocelli is the postocellar line (POL). Behind the posterior ocelli there is usually a transverse carina, the occipital carina. The region of the head posterior to this is the occiput. The area of the head located between the occipital carina, the inner orbits (margins) of the eyes, and the anterior ocellus is the vertex, and the region posterior to the eye on either side of the vertex is the temple. The area between the ventral margin of the eye and base of the mandible is the gena, and the distance between the ventral edge of the eye and mandibular articulation is the malar space. Often a suture, the malar groove, is present."

"The most obvious structures on the frontal aspect of the head are the antennae. The antennal toruli are the sockets of the antennae. The prominent carina between the toruli is known as the interantennal crest. The area of the head between the toruli, the inner orbits of the eyes and the anterior ocellus is the frons (defined by Graham 1969), and the area between the toruli, the eyes, and the clypeal edge is the face. The clypeus often is a poorly defined mesal region above the oral margin and demarked by the epistomal suture. The scrobes are one or two depressions often present on the frons in which the antennal scape lies at rest."

Antennae.-- "The antennae of chalcidoids consist of the scape, pedicel, and flagellum. A narrow, sometimes elongate, radicle (basal prolongation of scape) connects the scape to the head. The flagellum usually is multisegmented and in the female generally differentiated into 1-4 tiny anelli (ring segments), a funicle with 0-7 segments, and a club (clava) with 1-5 segments. The male antennae are branched (e.g., Eulophidae and Encyrtidae), and usually do not have a club differentiated from the funicle segments."

Mesosoma.-- "The mesosoma, or true thorax, consists of three segments, the prothorax, mesothorax, and metathorax. Posterior to the metathorax is the propodeum, the first abdominal segment, which has become fused with the thorax. Because of its intimate fusion with the thoracic segments it is more convenient to consider the propodeum as part of the mesosoma."

"The prothorax consists largely of the dorsal sclerite, the pronotum which is variable in shape, an important distinguishing character at the family level. The lateral edges of the pronotum invariably are reflexed ventrally to cover most of the lateral part of the prothorax. The lateral metapleuron, like the mesopleuron, is usually separated into metapisternum and metepimeron by a metapleural suture."

"As noted previously, the first abdominal segment has become fused with the thorax and is known as the propodeum. it bears a pair of spiracles near its lateral edges and often a number of taxonomically important carinae. These are the median carina, plica (lateral carina), and costula (horizontal carina). The apex of the propodeum where it is attached to the gaster may be slightly projected; this projection is known as the nucha. The lateral area of the propodeum laterad of the spiracles is the callus."

Wings.-- By and large they are poor fliers and generally confined to their host habitats. The venation of the fore wing of winged chalcidoids is reduced to a single composite vein, which generally consists of the submarginal, marginal, and postmarginal veins, and often a small stigmal vein projecting between the marginal and postmarginal veins. The stigmal vein often is expanded into a knoblike structure at its apex, the stigma, and this may have a hook, the uncus. The thickened region of the submarginal vein adjacent to the marginal vein is the parastigma. Other obsolescent veins may be indicated on the wing by ridges or hairlines, in particular the basal vein and cubital vein. The speculum, a bare region, is present posterior to the parastigma and bounded in part by the basal and cubital veins. A radial cell may be delineated by the stigmal vein and macrotrichia extending from the stigma toward the apex of the wing. A row of setae below and parallel with the marginal vein are the admarginal hairs. The central part of the wing is the disc. Some proctotrupoids have a similar venation, especially those of the subfamily Telenominae. However, unlike proctotrupoids, in chalcids the pronotum does not reach the tegulae because the unique postspiracular sclerites are located here.

Legs.-- The legs are composed of the coxa, trochanter, femur, tibia, and tarsus. The trochanter is two-segmented in all chalcidoids except the Mymarommatidae in which the parts have coalesced into a single segment. The tibia apically has one or two tibial spurs; the number of spurs on the fore, middle, and hind legs is known as the tibial formula, e.g., 1-1-1, 1-1-2, 1-2-2. The tarsus is three- to five-segmented; the number of segments is an important distinguishing character at the family level."

Gaster.-- The gaster comprises the abdominal segments posterior to the propodeum, including the petiole, which connects the gaster to the propodeum. In many chalcidoids the petiole may be reduced to an inconspicuous ringlike segment, broader than long, in which case the gaster is said to be "sessile." If, however, the petiole is relatively long and conspicuous, longer than broad, the gaster is said to be "petiolate."

"There are seven gastral segments posterior to the petiole, although not all may be visible, and the ultimate segment is actually the fused remnants of the apical four abdominal segments. The dorsal sclerite of each segment is the tergite, whereas the ventral sclerite is the sternite. The penultimate tergite (t6) bears the only pair of functional spiracles on the gaster. The ultimate gastral tergite bears a small pair of fine hairs, the pygostyli (cerci). The apical segment also has a dorsal and ventral arch, the epipygium and hypopygium, respectively. In most females a pair of ovipositor sheaths, which protect the ovipositor when at rest, project from the apex of the gaster. The degree to which these project is an important distinguishing character for some families."

On economic importance, Yoshimoto (1984) stated that "The more important groups of chalcidoids, such as Aphelinidae, Eulophidae, Trichogrammatidae, Mymaridae, Encyrtidae, Eurytomidae, and Pteromalidae, are widely used in controlling or suppressing economic pests, both of forest and agricultural crops and those of public health importance. The use of these parasites is an important means of control alternate to chemicals, pathogens, or predators. The practice of integrated control using the above methods is being widely used to suppress target pests of great economic diversity, especially where chemical control measures are not feasible (DeBach 1964; Huffaker & Messenger 1976; Kilgore & Doutt 1967)."

Information courtesy of University of California, Riverside