Checklist of UK Recorded Aphelinidae

The family is large and contains parasitoids most often encountered as primary on homopterous families Aphididae, Coccidae and Aleyrodidae.

Description & Statistics

Aphelinids are a moderately sized, cosmopolitan family with circa 44 valid genera and 808 species by 1993. Important morphological characters are antennae with 8 or less segments; parapsidal sutures complete but shallow; and middle leg tibial spur long but not thick. The body is small, yellow or brown, and the gaster is broad at its base. Most species are primary, solitary, endoparasitoids of mealybugs, scale insects, whiteflies and aphids. However, some species parasitize eggs and others are hyperparasitic. Various species of aphelinids may attack all host stages. The family is important in biological control, having been used worldwide, especially against scale insects and aphids.

The better known common genera developing internally are Aphelinus in Aphididae, Coccophagus and Aneristus in lecaniine Coccidae, Encarsia and Eretmocerus in Aleyrodidae, and Prospaltella in diaspine Coccidae and Aleyrodidae. Aphytis spp. are ectophagous parasitoids of diaspine Coccidae, and larvae of several species have been found feeding on host eggs (Clausen 1940/62). Clausen also noted that there were a number of host records on other orders and families. Centrodera xiphidii Perk. parasitizes eggs of the locustid, Xiphidium varipenne Swezey in Hawaii and also was reared as an internal parasitoid of mature larvae of Haplogonatopus, a dryinid parasitoid of leafhoppers. C. cicadae Silv. develops in eggs of Cicada plebeja Scop. in Italy, and Centrodera speciosissimus Gir. is an internal parasitoid of larvae and pupae of the Hessian fly in North America.

When hyperparasitic, aphelinids may be found parasitizing mature larvae and pupae of several members of their own family and of other Chalcidoidea within the host remains, Ablerus being a well know example. A. clisiocampae Fitch is sometimes reared in abundance from the eggs of the eastern tent caterpillar, Malacosoma americana F., while A. macrochaeta var. inquirenda Silv. kills circa 50% of various primary species that attack Aleurocanthus spp. in tropical parts of Asia. Marietta (Perissopterus) is frequently associated with a wide variety of Coccidae, and it is thought that all members of the genus are hyperparasitic (Clausen 1940/62). Male progeny of several species of Coccophagus develop only hyperparasitically, whereas females are primary in habit.

Aphelinidae have been of great value in the biological control of coccids that do not respond well to other forms of control. Clausen (1940) noted the following species which have been credited with effective biological control: Aphelinus mali Hald on Eriosoma lanigerum Hausm.; Aspidiotiphagus citrinus Craw. on Aspidiotus destructor Sign.; Coccophagus gurneyi Comp. on Pseudococcus gahani Green; Encarsia formosa Gahan on Trialeurodes vaporariorum Westw.; Eretmocerus serius Silv. on Aleurocanthus woglumi Ashby; Prospaltella berlesei How. on Aulacaspis pentagona Targ.; and Prospaltella smithi Silv. on Aleurocanthus spiniferus Q.

Gibson (1993) remarked that the Aphelinidae the had body lengths of 2 mm or less and relatively lightly sclerotized. They are frequently dark parasitoids with at most an obscure metallic hue. The antennae are usually with at most 6 distinct flagellar segments (rarely 7-9 including an obscure ring-like basal segment); females have at most 4 distinct flagellar segments between the pedicel and club. Males do not possess a distinct club. The pronotum is usually much shorter than 1/2 the length of the mesoscutum and often appears linear in dorsal view. The mesoscutum have the notauli somewhat straight, complete and widely separated at the transscutal articulation near the anteromedial angles of the axillae. The axillae are relatively small, with anteromedial angles widely separated, usually partly advanced anterior to the scutellum. The prepectus is flat posterior to the pronotum, with the anterodorsal point of articulation anterior to or posterior to the insertion of the pl2-t2c muscle, sometimes also with a internal prepectal strut between the ventral angle of the prepectus and the mesoscutum. Individuals usually are fully winged but some females are partially apterous. The forewing has the marginal vein relatively long; the stigmal vein is short and postmarginal vein either absent or not extended beyond a point in line with the apex of the stigmal vein. Sometimes the stigmal and postmarginal veins are both long, but in this case the parastigma (= curved apical part of the submarginal vein) is usually extended like a spike onto the membrane behind the submarginal vein and bears 1-2 prominent long bristles. The mesopleuron is usually with a distinct mesepisternum and mesepimeron is separated the a fine groove and then with or without a small subalar acropleuron. But the acropleuron is sometimes enlarged and rarely comprises the entire mesopleuron. The mesothorax in ventral view is without a membranous area anterior to the mesocoxa (except in Coccobius). The mesotrochantinal plate and metasternum abut and either they have the metasternum extended anteriorly and ventrally to the mesotrochantinal plate (the metasternal pit is widely separated from the anterior margin of the metasternum), or the mesotrochantinal plate extends dorsally to the transverse margin of the metasternum (in this case the metasternal pit is very near the anterior margin of the metasternum). It is sometimes necessary to remove the mesocoxae to observe the characters. The protibiae have relatively long, curved apical spurs; the mesotibia dorsoapically, and mesotarsus ventrally, are without pegs (except in some Eutrichosomella). The mesotibial spur is quite long and often robust. The metatibiae sometimes bear long pronounced bristles. The tarsi usually have 5, sometimes 4, tarsomeres. The propodeum is usually conspicuously transverse, with the metasoma widely attached to the mesosoma. The cercus is not noticeably advanced anteriorly (Gibson 1993).

The family is widely distributed. Although circa 100 nominal genera have been described, only circa 40 are considered valid. About 1,120 nominal species have been described as of 1995. Concepts of family membership and relationships are not satisfactory, and aphelinids have been classified as a subfamily in both Encyrtidae and Eulophidae. Woolley (1988) believed that Aphelinidae is paraphyletic relative to Signiphoridae, with the latter family most closely related to Azotus and Ablerus. Gibson (1993) noted that genera that sometimes are classified as the subfamily Eriaporinae (these genera also sometimes are classified as a separate family, Euryischidae) pose a special problem. Specimens differ from Aphelinidae in the strictest sense by having well developed stigmal and postmarginal veins. One of the included genera, Euryischia, has disc-like compressed metacoxae. The metanotum extends posteromedially into a flat triangular plate. The propodeum is relatively long medially, and two robust metatibial spurs, similar to Elasmidae. Specimens of other eriaporine genera appear less like Elasmidae and are more typically Aphelinidae, except for the wing venation. Gibson (1989) suggested that Signiphoridae and Aphelinidae are sister taxa, based on the structure of the metasternum, and that this and the structure of the prepectus indicate that eriaporines are wrongly placed in the Aphelinidae. But, exact relationships with Aphelinidae and Elasmidae are not certain, and Gibson (1993) includes eriaporines as a subfamily of Aphelinidae for convenience. It was suggested by Bou…ek (1988a) that the subfamily Mongolocampinae, now in the Tetracampidae, might be better placed in the Aphelinidae.

Aphelinidae, with the Encyrtidae, is one of the most important chalcidoid families in biological control. Species are primary endo- or ectoparasitoids of primarily Aleyrodoidea, Aphidoidea, Auchenorrhyncha, Psylloidea and Coccoidea (Homoptera). They also parasitize eggs of Lepidoptera and Orthoptera, the eggs, larvae and pupae of Diptera, and the larvae of other chalcidoids and Dryinidae. This family is especially known for its frequent complicated modes of development and parasitism involving different hosts for the sexes. In some species the females are endoparasitoids and the males ectoparasitoids of the same host species, while in others the males are hyperparasitoids of females of their own species (obligate adelphoparasitism or autoparasitism), of other aphelinid species (facultative adelphoparasitism), or of other primary parasitoids.

Key references are Hayat (1983) and Jasnosh (1983), who keyed the world genera (the eriaporine genera were not included by Jasnosh). Jasnosh (1976, 1979) reviewed subfamily classification and summarized the hosts for aphelinid genera, respectively. Ferričre (1965) revised the aphelinid fauna of Europe and the Mediterranean Basin, Nikolskaya & Jasnosh (1966) of the European USSR and the Caucasus, and De Santis (1948) of Argentina. Rosen & DeBach (1979) monographed the world Aphytis. Compere (1947), Shafee (1975), and Hayat & Verma (1980) discussed classification of the eriaporine genera. Flanders (1967) related adelphoparasitism with ovipositional behavior.

Specific Geographic Areas

NEARCTIC (CANADA).-- Yoshimoto (1984) noted that the Aphelinidae consist of 41 known genera and some 700 described species (Rosen & DeBach 1979), and Hayat (1983) revised the world genera of Aphelinidae, including 44 valid genera. Of these, 20 genera and 120 species are known in North America. The family has contributed many biological control species. Species are small nonmetallic yellowish to black. Most are circa 1 mm. long, and the body is often stout and short, with a broad gaster.

Yoshimoto (1984) stated that "members of this family sometimes closely resemble either trichogrammatids or encyrtids. They may be distinguished from Trichogrammatidae by the following characters: Tarsi 4- or 5-segmented. Marginal vein in fore wing long. Mid tibial spurs long but not thickened. Mesopleuron divided by suture into mesepisternum and mesepimeron except in the genus Centrodora Förster and in other related genera. Centrodora Förster and other related genera are the only atypical genera of the Aphelinidae and, because of the preceding characteristic, it bears a close resemblance to the Encyrtidae and Eupelmidae. The aphelinids can be distinguished from the Encyrtidae by venational characters, and from the Eupelmidae by the following characters: Antennae not more than 8-segmented. Eyes large. Pronotum short. Notauli distinct."

Aphelinids have been placed among the Eulophidae and Encyrtidae, or as the family Aphelinidae (Rosen & DeBach 1979). Yasnosh's (1979) classification is based on biological data, but its use is limited because of the overlapping of host preference between subfamilies and diversity of hosts within the subfamilies (Yoshimoto 1984). The morphological characters do not agree with Yasnosh's biological separation.

Three subfamilies were recognized by Rosen & DeBach (1979): Aphelininae, Coccophaginae and Calesinae. Their monograph of aphytis of the world is based on biology, host preference, and very small differences in anatomy for species separation. Yoshimoto (1984) agreed with Compere & Annecke (1961), Rosen & DeBach (1979) and Hayat (1983) that Aphelinidae should be considered a distinct family. However, he followed De Santis (1946, 1948, 1967) and Rosen & DeBach (1979) for subfamilies, dividing the North American species into two subfamilies, Aphelininae and Coccophaginae.

Yoshimoto (1984) provided a key to the two subfamilies of Canadian aphelinids and discussed details of the subfamilies.

Aphelininae.

This subfamilies contains small to minute forms ranging from 0.5 to 2.0 mm. long. The group is separated from Coccophaginae by the tridentate or bidentate mandibles; antennae with 3-6 segments (0-3 funicle segments, 1 club segment); fore wing with bare oblique band; marginal vein as long or longer than submarginal; stigmal vein very short; postmarginal vein absent; tarsi with 5 segments.

North American Aphelininae are represented by 5 genera of which Marietta Motschulsky, aphytis Howard, Aphelinus Dalman, and Centrodora Förster (= Tumidiscapus Girault) are found in Canada (Yoshimoto 1984). The species are primary external parasitoids of aphids (e.g., Aphelinus), hyperparasitoids on hymenopterous parasitoids of scale insects (e.g., Marietta), egg parasitoids of tettigoniids and cercopids (e.g., Centrodora), and pupal parasitoids of cecidomyiids (e.g., Centrodora) (Yoshimoto 1984).

Coccophaginae.

There are 10 Nearctic genera of this subfamily, which differs from other subfamilies by having tridentate mandibles; antennae with 7-9 segments (scape, pedicel, 3 funicle segments, 1-3 club segments); pubescent fore wings, without a bare area (or speculum); distinctly longer marginal vein than submarginal vein; stigmal and postmarginal veins very short; tarsi have 4-5 segments (Yoshimoto 1984).

Canadian Coccophaginae are represented by Azotus Howard, Archenomus Howard, Eretmocerus haldeman, Coccobius Ratzeburg (= Physcus Howard), Encarsia Förster, and Coccophagus Westwood. Viggiani & Mazzone (1979) synonymized Aspidiotiphagus and Prospaltella with Encarsia. Species are hyperparasitoids on hymenopterous parasitoids of hard scales and white flies, and internal primary parasitoids of hard scales, soft scales and mealybugs. Several species have been widely used in biological control.

PALEARCTIC (EUROPEAN former USSR).-- Yasnosh (1978/1987), as translated from the Russian, described this family as "Body length usually less than 1.0 mm, rarely reaches 2.0 mm, and usually short and compact, yellow or brown, sometimes black. Antennae with not more than nine segments. mandibles with three teeth, with one to two teeth and cut, or rarely without teeth. Parapsidal grooves of shield of mesonotum complete. Sides of mesothorax more or less bifurcate. Marginal vein of forewings long, radial vein short, postmarginal vein generally absent. Spur of middle tibiae usually long and slender. Abdomen attached to thorax through broad base; the 7th, last sternite, varies in length and shape. Outer plates of ovipositor with ridge or carina (apodeme). male genitalia without parameres and cuspidal parts. Sexual dimorphism not distinct and evident mainly in differences in structure of antennae and coloration of body."

"Hosts of aphelinids comprise five orders: Homoptera, Orthoptera, Hymenoptera, Diptera and Lepidoptera; however, most aphelinids are associated with Homoptera, predominantly coccids, aleyrodids, and aphids. Eggs usually elongated-oval or oval. Larvae of aphelinids endo- and rarely ectoparasites; among Aphelinidae, secondary parasitism by the male and primary parasitism by the female of the same species is widespread (complete ditypism). Pupa with more or less distinctly segmented abdomen, antennae, legs, and rudiments of wings. Color of mature pupa constant. The meconium of larvae which have completed feeding looks like black or brownish particles of globules, and its shape and arrangement are characteristic of many species. Aphelinids are almost universally distributed, but mainly in the tropical regions of the world. More than 700 species are known from 41 genera; of these, 115 species from 24 genera have been found in the Soviet Union, and 87 species from 21 genera in the European part of the USSR and Trans-Caucasus."

AFRICA.-- Prinsloo (1980) commented that "Apart from the Encyrtidae, the aphelinids are the best known group of Ethiopian Chalcidoidea. Much has been published on this family, especially in southern Africa, and Annecke & Insley (1971) provide a catalogue to the fauna of the Ethiopian region."

Relationships & Diagnosis.--"The Aphelinidae share a number of characters with both the Encyrtidae and Eulophidae, and have been treated as a subfamily of both these two groups at one stage or another. However, most modern authors regard the Aphelinidae as a distinct family. Like the eulophids, aphelinids have a reduced number of antennal segments, axillae which are projected forwards, a fragile body, and tarsi in some species which have only four segments. Host preference shows a relationship with the encyrtids, and in the genera Marietta and Physcus, the mesopleura are large and convex, a character found otherwise only in the Encyrtidae and in females of the Eupelmidae. The aphelinids are distinguished from the families mentioned here mainly on a combination of characters, as mentioned below."

"Usually small chalcidoids, often less than 1 mm in length; body fragile and finely sculptured; integument never with a metallic lustre; antenna usually with three to eight segments, rarely with nine, the funicle at most with four segments, the club one- to three-segmented; mesoscutum with parapsidal sulci always developed; axillae broadly separated mesally, their anterior margins more or less projected forwards; fore wing with marginal vein extremely long, much longer than the very short stigmal and postmarginal veins; tarsi usually five-segmented, but sometimes also with four segments; abdomen with gaster broadly sessile; ovipositor never protruding strongly."

Biology.-- "Aphelinids are diverse in their biologies. They develop either internally or externally, some species being primary parasitoids, whereas others are hyperparasitic. In a number of species the females develop as primary parasitoids and the males as hyperparasitoids whereas in many others their biology and ontogeny are known to be very complex, resulting in many studies on the subject. Many aphelinids are rather host-specific, and a number of the well known genera are easily identified if their hosts are known. Eretmocerus and Encarsia are exclusively parasitic in whitefly (Aleurodidae), whereas the species of Aphelinus attack aphids; A. mali (Haldeman), introduced into South Africa from North America, is a well known and successful natural enemy of the woolly apple aphid, Eriosoma lanigerum. Aphytis, a large cosmopolitan genus, comprises many species which have been used in biological control programmes against diaspidine scale insects, and in South Africa a complex of Aphytis species successfully controls the citrus red scale, Aonidiella aurantii Mask. under favourable environmental conditions. Coccophagus is another large cosmopolitan genus which is richly represented in Africa, and many of its species are important parasitoids of soft scale insects; they are rarely also parasitic in mealybugs. Azotus and Marietta species are probably all hyperparasitoids and primary hosts of the latter genus include coccophagus and the encyrtid genus Habrolepis. Centrodora is unique in that its species are egg parasitoids of Orthoptera, and also of Homoptera."

African Aphelinidae.-- "Of the 40 odd genera of aphelinids, about 25 have been recorded from Africa. These genera may be divided into four subfamilies, although recent studies have suggested that the family be divided into seven subfamilies with a number of tribes of the subfamily Pteroptricinae are all characterized by the four-segmented tarsi. This subfamily is not well represented in our region, and is best known through the genera Archenomus and Eretmocerus, the latter genus being characterized by a long banana-shaped antennal club and two small funicle segments in the female. The Eriaporinae is another small group represented by three rather atypical genera which have also been placed in the family Elasmidae... The Coccophaginae is the largest of the subfamilies, and its members are separated from those of the Aphelininae in that they lack the broad, oblique hairless band (speculum) on the disc of the fore wing. Coccophagus, Aspidiotiphagus, Azotus and Encarsia are perhaps the more common genera of this subfamily. Marietta is one of the most common genera of the Aphelininae and its species are easily distinguished by their striking appearance, the legs and body being boldly marked in a zebra-like design, the fore wing usually with patches of contrasting colour. Aphytis is by far the largest aphelinine genus, comprising some 90 species distributed in all parts of the world. The species of this genus are usually small, fragile and usually yellowish in colour with the antennal funicle three-segmented, the basal two segments being smaller than the distal one." (Also see Annecke & Insley 1971, 1974, Ferričre 1965, Janosh 1976, Rosen 1993, Rosen & DeBach 1979).

INDIA & ENVIRONS.-- Hayat (1988) noted that "The family Aphelinidae contains small to very small chalcids that rarely exceed 1.5 mm. in length. These are usually yellow or brown in colour and soft-bodied insects. Inspite of their small size, the taxonomic studies on this family began very early in the nineteenth century. These gained impetus when the role of aphelinids as possible agents in the control of insect pests of economically important fruit and vegetable crops came to be recognized. This aspect of aphelinids attracted quite a few very brillient taxonomists and economic entomologists with the result that the taxonomy of this family is now relatively better known and understood."

History.-- "The literature on the family is vast inspite of its moderate size (49 genera). Reviews were earlier published by several authors. A full bibliography pertaining to the original descriptions of all the genera was recently given by Hayat (1983). I will, therefore, mention here only the names of some of the major contributors to the family."

"The earlier workers on the taxonomy of Aphelinidae include Dalman, Westwood, Walker, Foerster and Thomson. These were followed by the American entomologist, L. O. Howard who made major contributions to the family. Later, Mercet (on the Palaearctic fauna) and Compere published quite valuable papers in which they successfully tried to put the taxonomy of the family in order. The Australian fauna was almost exclusively dealt with by Arsene A. Girault, but because of his method of work, it was only recently that his genera were clarified taxonomically, mainly b Hayat. Among other workers who made substantial contributions to the family may be mentioned (the late) Ferričre, (the late) Annecke, De Santis, Janosh, and Viggiani. To Graham goes the credit for putting the taxonomy of the Palaearctic aphelinids in order."

"Studies on the taxonomy of the Indian aphelinids began rather late. Till the middle of this century only about twenty species were known. Since 1960, and mainly due to the works of Agarwal, Hayat, Shafee and Subba Rao, several species were described. Presently, the aphelinid fauna of the Indian subcontinent is relatively better known being represented by twenty-six genera and approximately 150 species."

Classification.-- Aphelinids are currently mostly treated in a separate family, Aphelinidae. Thee are still a few authors (for instance, Gordh in Krombein et al. 1979) who regard these a subfamily of Encyrtidae. it is extremely difficult to refute its status as a subfamily of either Encyrtidae or Eulophidae, or its independent family status. There are some genera in almost every family of Chalcidoidea, which differ so much from the accepted or supposed limits of a family (eventually conjectured on the basis of its so-called 'type-genus'), that one is apt to consider these as an indication of a relationship with or even as support for inclusion of the whole group or genus in, another family; or more inappropriately, as a case for the erection of a 'new' family. There are thus in Aphelinidae some genera that appear closer to Encyrtidae (Marietta, Coccobius, Eutrichosomella) and some appear closer to Pteromalidae (Promuscidea), but the majority, on the other hand, might be supposed to be an offshoot of Eulophidae or eulophid-like ancestors. In such a situation the logical course is to maintain the existing family names. I have therefore treated aphelinids as an independent family."

Hayat (1988) commented that the suprageneric classification of the family was considered in the past by several authors (De Santis 1946, Ferričre 1965, Nikol'skaya & Jasnosh 1966, Jasnosh 1976, Shafee & Khan 1978, Khan & Shafee 1980, Compere 1947, Ghesquičre 1955, Erdös 1964, Hayat 1978, Hayat & Verma 1980, Shafee 1974, 1975 and Viggiani 1981). In Hayat (1988) the following classification was presented: Family Aphelinidae: Aphelininae (Aphelinini, Aphytini, Eutrichosomellini); Eriaphytinae; Eriaporinae (Eriaporinae, Euryischiini); Coccophaginae (Coccophagini, Pteroptricini, Azotini). A key to the genera of Indian Aphelinidae followed.

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Biology & Behavior

Many early researchers did extended studies on Aphelinidae which revealed a majority of the known characteristics of these parasitoids. In particular Lundie (1924) did studies on Aphelinus mali Hald, Hartley (1922) on A. semiflavus How., Taylor (1935) on Aphytis chrysomphali Mercet, Phycus intermedia Gahan and Casca (= Pteroptrix) parvipennis Gahan; Imms (1916) and Griswold (1925) on A. mytilaspidis LeB.; Clausen & Berry (1932) on Eretmocerus serius Silv.; and Cedańa (1937), Flanders (1936, 1937) and Smith & Compere (1926, 1928) on a number of Coccophagus spp.

Aphelinids that are parasitic on Coccidae usually limit attacks to female hosts, probably because of their greater size. However, cosmopolitan A. chrysomphali attacks both female hosts and male prepupae and pupae. Schweig & Grunberg (1936) nevertheless believed that the attack is confined to male scales of Chrysomphalus aonidum L. in Israel and that 70-80% parasitization results in reduced infestations through lack of fertilization of some females. Both sexes of Aspidiotus destructor Sign, are attacked by Aspidiotiphagus citrinus agilior B. & P. and Casca parvipennis Gahan (Taylor 1935). The order of preference is believed to be related directly to the thin scale covering in Aphytis chrysomphali attacking many diaspine Coccidae (Clausen 1940/62).

In Coccophagus gossypariae Gahan, a parasitoid of the European elm scale, Gossyparia spuria Mod. in North America, the first generation develops only in male scales and the second in mature females (Griswold 1927). Adults of the second brood are larger resulting from the greater amount of food available to larvae.

Aphelinids show a considerable latitude in the stage of host development that is suitable for attack. Younger aphids were found to be preferred by Aphelinus semiflavus, but attack was successful on all stages (Hartley 1922). Although development of Aphytis chrysomphali on both male and female Aspidiotus is possible, there is a preference shown for mature females, including those which have begun to oviposit. Griswold found that the first generation of Aphytis mytilaspidis develops on 2nd instar Aspidiotus, etc., the 2nd generation on mature females and the 3rd either on these of on the eggs. When hyperparasitic, attack is limited mainly to mature larvae and pupae. In some species of Coccophagus, there is a sex differentiation in host relationships of complex and varying nature, as will be noted in a later discussion.

Adult Behavior.--Aphelinids parasitic in aphids emerge through a circular hole cut dorsally in the integument of the host remains near the posterior body end. Coccophagus spp. in lecaniine scales makes the emergence hole in the same position. Casca parvipennis, after developing in 2nd instar Aspidiotus, emerges anteriorly. Prospaltella and Eretmocerus parasitoids of Aleurocanthus, similarly emerge through a hole at the anterior end. Chrysomphalus aonidum cuts a hole or slit in the dorsum of the scale covering, and the flap thus formed is forced outward like a trap door. Male scales and females of species such as Aspidiotus destructor, which have delicate coverings, have parasitoids that emerge by merely pushing their way out from beneath the scale margin. Because of this the number of emergence holes is not satisfactory to access parasitization.

Adults of most species probably derive their food from honeydew secretions of their hosts. However, in aphelinus a large number of species feed on the fluids that exude from ovipositor punctures, with such feeding resulting in death of the aphid host. Hartley thought that A. semiflavus may be as effective in the role of a predator on Myzus persicae Sulz. as in its parasitic role. A single female usually kills 3-4 small nymphs daily through host feeding. Aphytis chrysomphali feeds at wounds made in the host body, but in this case puncturing the host body has no relation to oviposition, for it does not involve stinging. An unusual feeding habit was recorded in Coccophagus lycimnia Wlk by Quayle (1913), where females gouge out narrow strips of leaf tissue with their mandibles. Cedańa described details of the feeding of female C. scutellaris Dalm, on honeydew given off by scale insects. The habit was developed to such a degree that the parasitoid stroked the host with its antennae to induce it to excrete a drop of fresh honeydew, in a manner similar to ants.

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Immature Stages of Aphelinidae

The ovarian eggs of many species of the Aphelinidae that have been observed are of the two bodied type such as is found in several other families. At deposition the contents are forced into the main body, and the "bulb" remains as a somewhat collapsed stalk or hook. This form of egg is common to Aphytis, Centrodera and Aspidiotiphagus. In Marietta zebra, and other species, the laid egg (Fig. 80D) is much like the ovarian form except that the anterior stalk is appreci­ably reduced in size. This species is distinguished from others of the family by having the chorion of the main body covered with small papillae.

The eggs of Ablerus, Casca, Encarsia, Eretmocerus and Physcus, and those of Coccophagus of primary habit, are of sim­ple form, ranging from lemon shaped to kidney shaped and cylindrical. That of Eretmocerus serius (Fig. 81B) is distinctly flattened, owing presumably to its being compressed between the host body and the leaf after deposition.

Smith and Compere recorded an unusual modification in the egg of Euxanthellus philippiae Silv. The ovarian egg is sim­ple; yet after its deposition it is found to be attached to the host larva by a pedicel arising at the center of the ventral side (Fig. 80E). This pedicel apparently is formed in the same manner as that of the male eggs of Coccophagus Iycimni and C. heteropneusticus Comp., which are discussed in the following section, and it may, in fact, be a male egg, also.

The first instar larvae of the species that show no sexual dimorphism are of two types, the hymenopteriform and the caudate. The hymenopteriform larvae range from elongated to almost spherical in form and bear no appendages or integumentary setae. To this group belong the larvae of Aphelinus, Eretmocerus, Prospaltella, Aphytis and Aspidiotiphagus. The larva of E. serius (Fig. 81C) is pear shaped and shows no evidence of segmentation. Those of endophagous habit usually have only a simple internal tracheal system and no spiracles. Among the species that develop externally the number of spiracles is variable, ranging from five in M. zebra to eight in Aphytis mytilaspidis and A. longiclavae Mercet, though none was detected in Eretmocerus.

The caudate larva is not encountered frequently in this Aphelinidae, though it has been described for Aspidiotiphagus citrinus.

It is often difficult to determine the number of instars because of the minute size of the larvae and the lack of heavily sclerotized parts which might distinguish the suc­cessive exuviae. There are apparently only three, in contrast to the five found in sev­eral related families. The second and third instars possess no distinctive features and need not be described. The mature larvae usually have nine pairs of spiracles, though Coccophagus hawaiiensis and Aphelinus semiflavus are thought to have only five.

The pupae of a number of genera that attack diaspine Coccidae are conspicuous because of the extreme compression in the dorsoventral plane. In some species of Aphytis, the thickness is only one fourth the width of the body. The pupa of Physcus intermedia has an exceptionally heavily sclerotized integument, black in color and similar to that found in various Eulophidae.

Sexual Dimorphism in the Immature Stages of Coccophagus.

In the species of this genus that develop, in both sexes, as primary parasites, there is no departure from the normal of the family in the egg or larval forms, those of the two sexes being identical. Sex differentiation in host relationships in a group of species has involved a specialization in habits of the male that is reflected in several modifications in form to meet more successfully the conditions encountered. Flanders has described and figured the female and male eggs and early larval instars of several species.

The ovarian and laid female eggs of C. Iycimnia and C. heteropneusticus (Fig. 80A) are somewhat cylindrical, though slightly broader at one end, slightly curved, and smoothly rounded at both ends. The male egg (Fig. 80B, C), on the other hand, is drawn out at the anterior end into an irregular stalk like process which, at deposition, is twisted into a button like pedicel when it is inserted into a puncture in the host integument.

The first instar female larva of C. capensis (Fig. 82B) is of the caudate type, whereas the male (Fig. 82A) is of a distinctive form, having the segments clothed in long setae and the last abdominal segment extended into a long, spine like process. Both sexes have only an internal tracheal system. The male larva of C. scutellaris is of similar form.

The first instar female larva of C. heteropneusticus (Fig. 82C) is rather elongated and lacks an open tracheal system, whereas the male (Fig. 82D) is more robust and has spiracles on the last thoracic and the second, fourth, and sixth abdominal segments.

Coccophagus gurneyi has a first instar larva female (Fig. 82F) that is slender, tapering posteri­orly, and has only an internal tracheal system. The male (Fig. 82E) is of a modified planidium type, with heavily sclerotized segmental plates and two pairs of spiracles, situated on the intersegmental membrane just in front of the third and fifth bands, representing the first and third abdominal segments.

The ectophagous male larva of C. lycimnia is robust in form, with spiracles on the metathorax and on the second, fourth, and sixth abdominal segments.

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