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| Classification: Elasmidae (Family) (Chalcidoidea) |
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This is a comparatively small family which is usually represented by the genus Elasmus. Available host records show that they are either primary external parasitoids of the larvae of Lepidoptera or hyperparasitoids on them through various Hymenoptera, in particular the Ichneumonidae and Braconidae. A few species have been reared from the nests of Polistes (Vespidae), as primary parasitoids of their larvae (Gibson 1993). Some species develop regularly both as primaries and hypers. Hosts are usually attacked within a web, larval case or cocoon. Few species are abundant enough to be of any importance in the control of their hosts. However, a survey of parasitoids attacking Pectinophora gossypiella (Saunders) in northern areas of Western Australia by Sands & Hill (1982), showed that two species of Elasmus Westwood, E. broomensis sp. n. and E. bellicaput Girault, were reared. The Australian species of Elasmidae were revised by Riek (1967) but the life histories of most species were unknown.
The genera Euryischia and Myiocnema differ markedly in their host preferences from the remainder of the family and are considered to represent a connecting link with the Aphelinidae (Clausen 1940/1962). Euryischia lestophoni Riley is recorded from Australia as a hyperparasitoid of Icerya purchasi Mask. through Cryptochaetum, whereas Myiocnema comperei Ashm., also from Australia, has been reared from Saissetia oleae Bern. although its exact status has not been determined (Smith & Compere 1928). E. inopinata Silv. has been reared from dipterous larvae, possibly Syrphidae, in Sicily.
Elasmid adults of the genus Elasmus are very distinctive in appearance. They may be easily recognized by the compressed, triangular form of the body and abdomen and, in some species, by the arrangement of the setae of the hind tibiae in parallel lines or crossing to form diamond-shaped cells (Clausen 1940/1962).
Gibson (1993) remarked that in the Elasmidae the body was either brown or black to very yellow, usually with a slight metallic hue. The mesosoma and metasoma are wedge shaped in cross section. The head is somewhat lenticular, with the occiput sharply margined. The antennae have 7 flagellar segments in females and 8 in males, the basal segment is ring-like and the club has 3 segments. Males have a long ramus from the basal 3 segments of the funicle. The mesoscutum is noticeably setose, without notauli. The axillae are relatively small and widely separated, somewhat advanced anterior to the scutellum. The scutellum is usually glabrous except for 2 pairs of long sublateral setae, but rarely evenly setose with sublateral setae not obviously differentiated. The mesopleuron is almost flat, with only a very fine mesopleural groove and with the posteroventral angle extending slightly over the base of the metacoxa. The metanotum extends medially over the propodeum as a flat, triangular, usually yellowish or translucent lamina. The forewing is clearly elongated and narrow, the length about 3X or more its greatest width. The marginal vein is very long, the postmarginal vein short. The stigmal vein is sessile. The protibial spur is short and straight. The meso- and metafemora are compressed, somewhat elongated oval. The metacoxa is greatly enlarged and compressed, disc-like. The metatibiae usually have obvious short black bristles, these usually in more or less undulatory rows or a diamond pattern. The tarsi have 4 tarsomeres; the meso- and metatarsi are conspicuously elongated and slender, slightly tapering to the apex. The metasoma bears a transverse petiole.
The only genus generally recognized is Elasmus, but Riek (1967) established a second genus based on differences in the setal pattern of the meso- and metatibiae and relative length of the sublateral scutellar setae. Elasmus is most diverse in Old World tropics, but circa 260 nominal species occur worldwide. The family is sometimes classified as a subfamily of Eulophidae because of the number of tarsomeres and because of the structure of the protibial spur. However, some species of Aphelinidae are also similar in structure.
NEARCTIC (CANADA).-- Yoshimoto (1984) discusses Elasmidae as a subfamily, Elasminae, of the Pteromalidae. He noted that Graham (1969) and Bou…ek in Peck et al. 1964) also treated it as a family. Distinguishing characters are a 4-segmented tarsi; axillae produced far forward of scutellum; funicle with 3 segments in female, 4 in male (basal segments of male funicle bear 3 lateral branches); scutellum with 2 pairs of stout bristles; middle and hind femora enlarged, flattened; legs generally elongated and spiny; hind tibiae with short bristles in longitudinal rows forming elongated to diamond-shaped forms; entire body slender and elongated; gaster appears wedge-shaped; fore wings are long and somewhat wedge-shaped, with marginal vein sometimes very long (Yoshimoto 1984).
A key to the known North American Elasmus spp. was given by Girault (1918). Burks (1965, 1971) revised the North American species of Elasmus, the only genus found in Canada. Species are principally secondary parasitoids on Braconidae and Ichneumonidae that are found in lepidopterous and dipterous primary hosts, although one North American Elasmus polistis Burks, was recorded as a primary parasitoid of Polistes Latreille (Hymenoptera: Vespidae) (Yoshimoto 1984).
PALEARCTIC (EUROPEAN former USSR).-- Trjapitcyn (1978/1987), as translated from the Russian, noted that these were "Small chalcids; length usually 2.0 to 3.0 mm. Structure of thorax similar to members of Eulophidae, since axillae protrude slightly forward beyond imaginary line between tegular, and spur of foretibiae straight and rather short. Hind coxae usually broaden notably, flat, often almost discoidal; tarsi with four to five segments, usually long and slender. Marginal vein of forewings usually very long, in which case radial vein very short; parapsidal grooves of shield of mesonotum usually only slightly perceptible in front. Abdomen with very short petiole. Body black, with slight metallic sheen, sometimes more or less yellow. Antennae of male usually branched. Host range rather variable-- cocoons of minute species of Lepidoptera or their parasites, and larvae of flies (Diptera) and plaited-winged wasps (Vespidae). The family comprises two confirmed genera and more than 100 species, among which 12 species are found in Europe and 7 species in the European part of the USSR."
AFRICA.-- Prinsloo (1980) noted that the elasmids form a small family, considered by most authors to comprise a single genus, Elasmus. Hedqvist (1960) provided a catalogue to the African fauna. Prinsloo (1980) discussed Elasmidae further as follows:
Relationships & Diagnosis.-- "The elasmids are probably most closely related to the Aphelinidae and Eulophidae, and like the latter family, the tarsi also have four segments. However, the distinct shape of the hind coxa separates this small family from all other chalcidoid groups."
Small to moderate in size, varying from about 1-3 mm in length; integument yellow to black, at most weakly refringent, the head and thorax often with markings of contrasting colour; antennal funicle with three segments, in male always branched; club three-segmented; thorax with axillae projecting forwards; fore wing wedge-shaped; submarginal vein short, the marginal very long, reaching to near wing apex, the stigmal and postmarginal veins relatively very short; hind leg with coxa greatly enlarged, flattened plate-like in lateral view, the tibia with coarse dark setae arranged in a characteristic diamond-shaped pattern; abdomen with gaster sessile, tapering strongly towards apex; ovipositor not protruding caudally."
Biology.-- "Not much is known about the biology of the African species of Elasmus and our information is largely restricted to a number of host records; these include lepidopterous pest species such as the cotton leaf roller, coffee leaf roller and the cotton semi-looper. In general, species of Elasmus are known to be external primary parasitoids of the larvae and pupae of Lepidoptera, or secondary parasitoids of them through Hymenoptera, usually of the families Braconidae and Ichneumonidae. One African species, Elasmus masii Ferrière is a hyperparasitoid of Apanteles species (Braconidae) which attacks Diparopsis castanea (Hamps.), the red bollworm."
African Elasmidae.-- "As mentioned above, modern authors recognize only a single genus, namely Elasmus, recorded from the Ethiopian region by 25 species. Three other genera, namely Myiocnema, Euryischia and Eurymyiocnema have also been included in the past, but Compere (1948) discussed the status of these genera and placed them in the Aphelinidae. Recently Austelasmus, a genus very similar to Elasmus, was described from Australia, but it is not known from our region. Little is known about the African species of Elasmus and they are mostly known only from their original taxonomic descriptions."
INDIA & ENVIRONS.-- Verma & Hayat (1988) noted that "The family Elasmidae is an interesting group of chalcids characterised by the presence of large, flattened and disc-like hind coxae, presence of a triangular plate on the metanotum, a medially elongated propodeum, and a habitus that strongly reminds of a very bristly fly. The family is otherwise important as its members are mostly parasitoids or hyperparasitoids of lepidopterous larvae or their primary (mostly braconid) parasitoids."
History.-- "The family with its only genus Elasmus Westwood contains approximately 250 species. The major contributions to the taxonomy of the family were made by Ferriere (1929, 1947) on the Asiatic, African and Palaearctic species. Hedqvist (1960) catalogued all the known species from the Ethiopian region. Burks published a key to the Nearctic species of Elasmus. Riek (1967) reviewed the Australian species described by Girault and also proposed the genus Austelasmus. More recently, Trjapitzin (1978) gave a key to eleven species from U.S.S.R."
"The elasmid fauna of the Indian subcontinent is poorly known, being represented by 33 species. Till 1972 only seven species were known from the region. In 1972 Mani & Saraswat contributed a major paper in which they described fifteen species as new. Recently a few more species were recorded from India and two species were described from Pakistan."
Classification.-- The genus Elasmus was placed by Westwood (1840) in the subfamily Eulophinae (his Eulophides). Foerster (1856) proposed the 'family' Elasmoidae under Section B (Tetrameres) of 'Chalcidiae.' Thomson (1878), on the other hand, erected the tribe Elasmina in Section Microcentri. Howard (1894) treated elasmids in subfamily Elasminae of the older family Chalcididae. Ashmead (1899, 1904) placed elasmids in a separate family Elasmidae. This view is generally accepted by most of the recent workers, but Burks (1965, 1979) and Riek (1967) gave this group the rank of a subfamily in the larger family Eulophidae."
Few biological studies have been made on members of Elasmidae, with extended accounts by R. Rao and Cherian (1927) on Elasmus nephantidis Roh., parasitic on the coconut caterpillar, Nephantis serinopa Meyr., in India and by Taylor (1937) on E. hispidarum Ferr., attacking several species of coconut leaf miners of the coleopterous genus Promecotheca in Fiji.
Female E. nephantidis makes a close examination of the galleries of silk and frass formed by the host and seems to restrict her oviposition to those individuals which have just spun the cocoon and are in a quiescent prepupal condition. The female pierces the wall of the cocoon with the ovipositor, stings the caterpillar, and then lays 10-20 eggs near the body. These hatch within one day, and larval feeding is complete circa 4 days later. Mature larvae then congregate in one corner of the cocoon, cast their meconia and pupate.
Elasmus hispidarum does not differ greatly from those of E. nephantidis, although all stages of the active larva, rather than the prepupa of the host, are attacked. In oviposition, the underside of the coconut leaf is pierced by the ovipositor and the larva are stung into permanent immobility, and the eggs are then deposited in an irregular group within the mine. The number deposited seems to vary directly with the size of the host individual. Usually only a single egg is laid in the mine of a 1st instar larva, whereas those of the 3rd instar larvae receive 6-18. The latter is the maximum number that can develop to maturity on a single host. The young larvae wander about the mine in search of the host and die within 30 hrs if it is not found. The host larva dies within 12 hrs after the beginning of feeding by the parasitoids. The pupa of the parasitoid is attached at its posterior end to the wall of the mine by the meconium and the last larval exuviae, the latter being in the form of a thin, twisted thread(Clausen 1940/1962).
Pupae of Elasmus sp. parasitic on bagworm larvae in Japan, are similarly attached by means of the meconium and exuviae, but they are arranged in a ring about the inside of the case. Mating takes place immediately after adult emergence, and a gestation period of 2-3 days elapses before the beginning of oviposition.
Elasmus broomensis Naumann & Sands is a biparental, solitary, external parasitoid of the larvae of Pectinophora gossypiella. Adult wasps oviposit on half to full grown larvae when these are accessable in open cotton bolls, open seed pods of Gossypium australe F. Muell. or in tunnels which allow entry of the parasitoid. Wasps are not able to penetrate unopened cotton bolls with their ovipositor. Larvae in diapause are also attacked and appear to be preferred to non-diapausing larvae in the laboratory (Naumann & Sands 1984). Before oviposition, an adult wasp uses its antennae to palpate the plant tissues, fecal pellets and silken cocoons surrounding a P. gossypiella larva. On locating a host, a parasitoid pierces the silken chamber with its ovipositor and stings it, usually once on a posterior segment. In the laboratory up to 7 scars were observed resulting from multiple stinging. The host larva, when stung, moves violently at first but becomes paralyzed within 2-3 min. A single egg is deposited close to the host, unattached within the silken chamber, 5-8 min. after stinging. Naumann & Sands (1984) considered that E. broomensis may be a useful agent for the biological control of P. gossypiella. As part of a survey (Sands & Hill 1982), 21 species of Lepidoptera (including 5 Gelechiidae) were reared from the seed capsules of Malvaceae, but E. broomensis was not reared as a hyperparasitoid, despite the abundance of Apanteles oenone Nixon, a common parasitoid of P. gossypiella and P. scutigera (Holdaway).
Each egg of E. broomensis measures 0.44 mm X 0.12 mm, and is white and elliptical. Newly hatched larvae move onto the surface of the paralyzed host and begin to feed, usually commencing on the anterior segments. Between different feeding periods a parasitoid larva moves from one site to another on the same host. About 24 hr prior to pupation, the larvae void their meconia and pupate close to the host remnants. Within a few hours, pupae turn black. Each was found attached by a pedicel to the host's silken chamber. The duration of immature development is discussed by Naumann & Sands (1984).
Elasmus bellicaput Girault as studied by Naumann & Sands (1984) was reared as a primary external parasitoid of P. gossypiella in the laboratory. The duration of immature development differed slightly from that of E. broomensis: larvae taking 4 days from hatching to pupation at 25°C. Pupal development was similar to that of E. broomensis. This species has also been recorded as a hyperparasitoid from the cocoon of an Apanteles sp. on Earias (Girault 1926). Clausen (1972) noted that some Elasmus can develop either as primary- or hyperparasitoids. Naumann & Sands (1984) considered E. bellicaput as a poor choice for biological control of P. gossypiella because as a hyperparasitoid it would destroy the immature stages of Apanteles oenone Nixon, a potentially valuable primary parasitoid of this host (Sands & Hill 1982)
Life cycles of Elasmidae seem to be very short; development from deposition of the eggs to the emergence of adults taking 10-16 days for E. nephantidis and an average of 14.5 days for E. hispidarum at a mean temp. of 29°C.
Reproductive capacity is quite low; E. hispidarum could deposit only circa 50 eggs during a period of 1-2 months, and the same number was produced by E. nephantidis during a much shorter life. Voukassovitch (1932c) mentioned that the ovaries of E. flabvellatus Fonsc. comprise only three follicles each and contain only a small number of developing eggs, showing a capacity approximating that of the above-mentioned species. The number of individuals developing to maturity on a single host is usually much greater than that indicated for the foregoing species. W. D. Pierce recorded 118 E. zehntneri Ferr. from a single caterpillar of Topeutes (Scirpophaga) intacta Sn.; Cherian & Israel (1937) reared a maximum of 170 of the same species from a caterpillar of the same genus in India, and the average for a series of host individuals was 75.
Sex Ratio.--There is often a marked variation in sex ratio correlated with host size. In E. hispidarum, males predominate in a 7:5 ratio when development is solitary on small hosts, but they are in the minority of 1:2 when several individuals develop on each mature host larva. The ratio is very variable among different colonies, but each always contains at least one male. A. W. Lopez observed a ratio of 8:1, with females predominating, in E. zehntneri in the Philippines, whereas Pierce, in rearings of more than 2,000 of the same species, found that only 8% were females. In a few cases where parthenogenetic reproduction occurs, the progeny are all male (Clausen 1940/1962).
The eggs of the Elasmidae are of simple form, either subcylindrical or kidney shaped in outline, the anterior end slightly the wider and both ends smoothly rounded. That of E. claripennis Cam. is stated to have a short peduncle at the narrower end, and in E. nudus Nees (Parker, 1924) the chorion is covered with minute tubercles.
The first instar larva is hymenopteriform, with the segmentation distinct and the body widest in the anterior abdominal region. That of E. hispidarum has a median row of fleshy pseudopodia ventrally, these being situated intersegmentally, the first between the second and third thoracic segments. In E. nudus (Fig. 78), the body is somewhat cylindrical and, like E. hispidarum, has spiracles on the second thoracic and the first three abdominal segments.
The second instar larva of E. hispidarum is similar to the first, as is also the third, except for the appearance of the nine pairs of spiracles, situated on the second and third thoracic and the first seven abdominal segments.
The mature larva, which is the fourth instar in E. hispidarum, bears a row of retractile intersegmental pseudopodia on the median line, both dorsally and ventrally. They are extruded only when the body is fully extended and presumably serve in locomotion within the host leaf mine. The spiracle number and arrangement in this species and in E. nudus (Fig. 78), also, are identical with those given above for the third instar.
The pupae of E. hispidarum and of an undetermined species reared from bagworms in Japan are distinguished by the extension of the scutellum into a distinct bifurcate process which in the latter species, extends over about one third of the length of the abdomen.
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