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Biology and Behavior

 

Eulophinae

Parker & Smith (1933a) gave an extended account of Eulophus viridulus Thoms., a parasitoid of the European corn borer, Pyrausta nubilalis Hbn.  It is a gregarious external parasitoid of the last three larval instars, and the number that develop on each host ranges from 2-3 to a maximum of 57.  The average of the summer generation colonies was 7.6 as compared with 16.5 for the autumn brood and 23.3 in the winter generation (Clausen 1940/1962).

 

Females have a long gestation period, and at no time is there a large number of eggs in their ovaries.  Host larvae are permanently paralyzed by the female's sting, and the eggs are laid indiscriminately on the body.  Larvae develop rapidly, and the host is reduced to an empty shell within a few days.  When mature the parasitoid larvae crawl some distance from the host and pupate in the host tunnel.  The meconium is case in the form of a series of blackish pellets, after which the final larval molt occurs.  The cast integument still envelops the tip of the abdomen of the pupa and fastens it securely on its dorsum to the wall of the tunnel.  When the adult is ready to emerge, the pupal skin breaks transversely at the neck and longitudinally for a short distance along the median dorsal line of the thorax.

 

Winter is passed in the pupal stage in the host tunnel.  Hibernation seems to involve a true diapause, for it is not possible to obtain early emergence by subjecting recently formed pupae to high temperatures.  There are three generations each year, and adults of the first brood emerge late in April and May.  The life cycle from egg to adult is circa 14 days under summer conditions. 

 

Females predominate in the ratio of circa 2:1 in the field, but many colonies have been found to consist of only one sex, particularly females.  Mating probably takes place in the host tunnel prior to emergence.

 

Microplectron fuscipennis Zett. is an external parasitoid of mature larvae, prepupae and pupae of the sawfly Diprion sertifer Geoff. and others of that genus in Europe.  Extended biological studies have been done in connection with its introduction to Canada for the biological control of spruce sawfly, D. polytomum Htg. (Morris & Cameron 1935, Ullyett 1936, Reeks 1937).  Oviposition occurs in the sawfly cocoons in rubbish on the surface of the soil or just beneath it.  The host is partially paralyzed and 20 or more eggs are laid on the body, although a maximum of 120 individuals are able to reach maturity in a cocoon of D. sertifer.  The average number varies greatly according to locality and ranged from 30.7 in Hungary to 72.5 in collections from Jugoslavia.  The maximum number of eggs obtained from a single female was 215, and the average number of progeny produced ranged between 40-57.  The number of cocoons that may be successfully attacked by a female is low.

 

The cycle from egg to adult is circa 20 days at 22°C.  Ullyett noted that although high RH is conducive to maximum oviposition, it has little influence on larval development.  This is due to the ideal conditions of the microclimate in the cocoon.  The optimum developmental temperature is 20-35°C.

 

Hibernation occurs in the larval, prepupal or pupal stages and appears to be a true diapausae for many individuals begin hibernation as early as August.  Morris & Cameron (1935) found that the sex ratio varied considerably in different geographic regions.  There is a great preponderance of females, ranging from 4:1 in Jugoslavia to 6:1 in Hungary, and the former ratio was secured also in a large series of laboratory experiments.  The lower Jugoslavian ratio may be correlated with the much higher number of individuals developing in each cocoon.  Reeks found that the ratio among progeny of females known to be mated was 9:1

 

Taylor (1937) studied Dimmockia javana Ferr, a solitary external parasitoid of the coconut leaf miner, Promecotheca nuciferae Maulik, larvae, in Java.  The preoviposition period ranged from 3-9 days and the oviposition capacity of females varied directly with their size.  The normal number of ovarioles was six, but small individuals have a smaller number, resulting in the production of fewer eggs.  The maximum egg deposition in one day was 18, representing 3 eggs per ovariole; but this occurred only when there had been no opportunity for oviposition for some time previously.  Attack may be on host larvae in any stage of development from late first instar onward.  Stinging of the larva inhibited further development, but the prepupa was able to complete its transformation.  However, the parasitoid was able to continue its development on the pupa provided that feeding began before the pupal integument hardened.  The sex ratio of progeny from small hosts was circa 1:1, and females predominated from larger hosts.

 

A departure from the normal hyperparasitic habit of the genus is found in Cirrospilus ovisugosus C. & M., which is predaceous on the eggs of the four-lined plant bug, Poecilocapsus lineatus F. (Crosby & Matheson 1915).  Host eggs are laid in clusters in plant stems, and the parasitoid larvae burrow through the pith until encountering a mass.  It then consumes 3-4 eggs before reaching maturity.  It is thought that Euolophinae which attack leaf mining larvae usually kill the host at the time of oviposition.  This habit is found in a number of species of Asympiesiella and Diaulinus, while Eulophus viridulus paralyses the host instead of killing it.  When hosts are killed, their bodies decompose rapidly, turn black and the contents liquify.  All this before completion of larval feeding.  However, in Cratotechus the host remains active.  Eggs of C. opaculus Thoms. and C. longicornis Thoms. are laid externally on the dorsum usually, and larval feeding commences at this point.  Eulophinae that attack hosts in mines, cocoons and tunnels usually oviposit loosely on or near the host body (Clausen 1940/1962).

 

Most species of Eulophinae have several generations each year, depending on availability of suitable stages for attack. Eulophinae also pass the winter primarily in the pupal stage, which is not typical of Chalcidoidea.  In some species there is a distinct diapause.  The second generation of Dimmockia incongruus pupae persist ca. 10 months, while the entire cycle of the first generations averages only 16 days. Microplectron fuscipennis, noted above, is an exception to this behavior.

 

The host is usually left when larval feeding is completed and pupation occurs in the surrounding area.  The last larval integument surrounds a portion of the pupal abdomen and serves to attach it to the leaf surface or to the wall of the mine, tunnel or cocoon.  Pupal integuments are very heavy, as in the Entedontinae, so that their form is retained after adult emergence.  Integuments are first white but quickly change to dark brown or even black.  Pupae either stand erect or frequently lie with their venters upward. Cratotechus species which develop on free living larvae of Lepidoptera on foliage, leave the host body and frequently pupate in a circle or ellipse about it, with heads directed toward the center (Clausen 1940/1962).  Such have been termed tombstone pupae (see Clausen 1940/1962).  Pupae are subject to a high degree of hyperparasitism when they occur on foliage without any covering, and a high percentage may be destroyed by other species of Eulophidae and related families.  Two color forms exist among pupae of E. viridulus, some of the summer generation having a relatively thin and brownish colored integument, while those overwintering are heavy and black (Parker & Smith 1933)

 

Tetrastichinae

Most tetrastichinids develop as internal parasitoids of the eggs, larvae and pupae of other insects.  Melittobia species, except M. indicum Silv., develop externally and are highly specialized in the host relationship and habits as follows:

 

Tetrastichus is internal in most cases, such as T. blepyri Ashm., which is hyperparasitic on Pseudococcus through several Encyrtidae, and T. radiatus Waterh., which attacks the nymphs of Chermidae.  There is a record of a parasitoid developing both as an internally and externally (Urbahns 1917).  Out of 111 parasitized larvae of the clover seed chalcid, Bruchophagus gibbus Boh (= funebrus How.) examined, 106 bore T. bruchophagi larvae externally and five internally.  A greater part of the larval development occurs in the host stage following that in which the egg was laid. T. asparagi Cwf. oviposits in the egg of the asparagus beetle, but larval feeding is not completed until the prepupal stage in the soil. T. giffardianus Silv. and M. indicum, that emerge from dipterous puparia, oviposit in the mature larvae just prior to pupation. T. crassinervis Thoms. is both a primary and a secondary parasitoid of Hyponomeuta malinellus Zell, and occasional individuals are found even in newly transformed adults, although they are unable to emerge (Voukossovitch 1932).  When hyperparasitic through Disochaeta, adults are unable to make an emergence hole and die (Clausen 1940/1962).

 

A great deal of diversity in host relationships is illustrated by the species of Tetrastichus, parasitic in Coccinellidae. T. ovulorum F. is a solitary internal parasitoid of the eggs of Epilachna in India, whereas T. epilachnae Girard and T. coccinellae Kurdj. oviposit in mature larvae or pupae but emerge only from pupae.  Both of these species attack predaceous beetles, and T. epilachnae additionally parasitizes phytophagous epilachna.

 

Even though most species of Tetrastichinae are parasitic in or on immature insects, several are also predaceous in habit. Ootetrastichus beatus Perk., attacking the sugarcane leafhopper, consumes the entire contents of the host egg chamber. T. schoenobii Ferr. was found by Pagden (1934) to be predaceous on the eggs of Schoenobius incertellus Wlk. in Malaya, and the larvae were also found feeding on young host larvae which remained beneath the egg mass for several days after hatching.  T. verrucarii Balduf, parasitic on larvae of Cynipoidea, have larvae that may move from one gall to a contiguous one, consuming the larval occupants. T. Eriophyes Taylor is usually predaceous as larvae and is limited for food to Eriophyesribis Westw. occurring on currant buds.

 

Some species such as Melittobia indicum, have a large number of mature eggs in their reproductive system at the time of female emergence.  Oviposition occurs immediately whether or not females have mated.  Clausen (1940) believed it probable that many species are able to do this, but M. acasta Wlk. has a gestation period of 11-12 days.

 

When adult females feed on the body fluids of the host, as in Melittobia, there is no noticeable effect upon the host individual and such feeding does not reduce population density.  Marchal (1905) reported host feeding for the first time on a T. xanthomelaenae Rond., attacking eggs of the elm leaf beetle.  However, in some Tetrastichus and other genera, adult feeding may destroy a greater number of hosts than parasitization.  Johnston (1915) recorded that 71% of 2,000 host eggs were consumed by female T. asparagi.  Feeding does not occur on eggs where oviposition takes place, however.  Several true egg parasitoids of Tetrastichus were noted to feed similarly.  Thus, the habit is identical with that in the ichneumonid, Diplazon laetatorius F. which shows a similarity in its host relationships.  Female T. coccinellae feed on fluids exuding from the wound made when attacking coccinellid larvae, and occasionally a feeding tube is constructed.

 

When oviposition occurs on exposed hosts, the female usually stands on the body and inserts her ovipositor perpendicularly.  However, this is often not possible if the host is active and insertion is then made by a forward thrust between the legs. M. indicum inserts her ovipositor in the posterior end of the abdomen of the active trypetid larva and may be dragged about by it.  These females frequently burrow into decaying fruit searching for their victims, which is also found in T. giffardianus.  When ovipositing on nymphs of Diaphorina (Euphalerus) citri Kuway, T. radiatus places eggs on the ventral side of the body near the juncture of the thorax and abdomen (Husain & Nath 1924).  When Thripoctenus russelli Cwf. attacks early stage thrips, the abdomen is curved beneath the body and the ovipositor is inserted near the caudal end, while in T. brui the female turns about and inserts it by a backward thrust into the lateral margin of the thorax.  Marchal concluded that the repeated insertion of the ovipositor by Tetrastichus xanthomelaenae into elm leaf beetle eggs may be to disorganize the contents and prevent completion of embryonic development.

 

Clausen (1940) discussed Tetrastichus rapo Wlk, an indirect secondary parasitoid of Ascia and other Lepidoptera through Apanteles, Microgaster, Anachaetopsis, etc..  It places its eggs in the body of its primary host while this is still within the live caterpillar, which is usually in its last instar.  T. rapo is obviously able to determine whether the active caterpillar contains a parasitoid larva without proving with the ovipositor.  The host relationship was first noted by Martelli (1907) and later verified by Gautier & Bonnamour (1924) and (Faure (1926).  Young caterpillars that re stung by the parasitoid frequently die from mechanical injury it is thought, though no eggs are laid.  This parasitoid may also be a direct parasitoid of larvae and pupae of these Braconidae in their cocoons (Clausen 1940/1962).

 

The pupal tsetse fly parasitoid, Syntomosphyruum glossinae Waterst., also develops as a hyperparasitoid through Mutilla.  In such cases the female reopens the perforation made in the puparial wall by Mutilla, using the hard pointed tip of the abdomen and oviposits through it (Clausen 1940/1962).  In many species of endoparasitic behavior, the female lays her full quota of eggs for development in a single host at one insertion of the ovipositor. T. giffardianus lays an average of eight in each host larva attacked, and Melittobia hawaiiensis Perk. when attacking puparia of Diptera, deposits circa 20 in each batch, and she may remain for many hours with the ovipositor inserted (Clausen 1940/1962).

 

Reproductive capacity data for Melittobia species indicates 1,086 eggs by M. acasta as the maximum, but most species range from 30-70.  Clausen (1940) reported on a female of Tripoctenus russelli as laying 38 eggs in one hour's time.

 

Faure (1926) noted that the eggs of Tetrastichus rapo were often found in the anal vesicles of Microgaster and Apanteles.  At deposition they are placed only in the general body cavity but then float free in body fluids and lodge in the vesicle where blood circulation is slower.

 

Larval habits of Tetrastichinae have not been elaborated on probably because there is a lack of any specialization or unusual events that merit notation.  The mature larva of T. ovivorax Silv.,  developing in Oecanthus eggs, emerges from the empty shell to pupate, which is not usual in egg parasitoids.  Pupation of those species which develop internally in larvae or pupae may be either within the body of the host or outside it.  The mature larvae of T. asparagi emerge from Criocerus prepupae and pupate in the cell containing it, while T. coccinellae pupates within the mummified host remains. T. crasinervis transforms within the pupa of its host lepidopteran.  Mature larvae of T. taylori Ferr. emerge from Elasmus larvae and pupate in the mine of the secondary host, but when development has been in a pupa or in a larva of Promecotheca, the transformation occurs within the empty host integument.  Mature larvae of T. radiatus utilize the host body as a covering and fasten it to the leaf surface with a few strands of silk prior to pupation, which is comparable with the habit of a number of species of Elachertinae on caterpillars.  Species of Tripoctenus that attack thrips, slough off the host integument but retain it as a crumpled mass enveloping the pupa's abdominal tip.

 

Many species of Tetrastichinae are solitary, particularly  those that are egg parasitoids of those of the genus Tripoctenus which develops on thrips.  However, even among the former there are some that produce 2-3 individuals in each host egg.  Among those attacking larvae and pupae, the maximum recorded is 338 Melittobia hawaiiensis on a single larva of Sceliphron, although Gater (1926) found 119 of what was regarded as the same species, from a puparium of Ptychomyia remota Ald. in Malaya.  In Tetrastichus asparagi only 5-6 can develop in each asparagus beetle larva, but an average of eight T. giffardianus in pupae of the Mediterranean fruitfly.

 

The life cycle of Tetrastichinae is relatively short, the minimum period from egg to adult was 6-10 days recorded for Tetrastichus ovulorum in India.  Most complete the cycle in 15-25 days, however.  Buckell (1928) recorded a large difference in time required for the development of males and females of Melittobia chalybii Ashm. under experimental conditions, males requiring only 21 days as compared with 37 days for females.  Related to the short life cycle, there is probably quite a few generations each year.  Although some species are restricted to a single generation per year that corresponds to the host, most species have 2-3. T. xanthomelaenae has nine generations each season in Italy.  This parasitoid is able to reproduce continuously during the entire period in which elm leaf beetle eggs are available in the field.  Thripoctenus brui Vill. shows a close adaptation to the life cycle of the host.  In northern Europe there is a single generation each year just as the host Kakothrips pisivorus Westw., while in Japan there are 4-5 generations on Thrips and Taeniothrips, both of which have several generations each season.

 

Hibernation often occurs in the mature larval stage in the host body or in the cell which contains it.  A portion of the brood of M. acasta may pass the winter in the pupal stage.  The hibernation habit of Tetrastichus xanthomelaenae was not determined, but no alternate hosts are known and it is thought that the adult females persist in sheltered places until the following spring. Thripoctenus russelli and T. brui pass the winter in the pupal stage.  Sometimes the immature stages of Tetrastichinae may go into diapause for a long period.  Parasitized pupae of Epilachna containing Tetrastichus epilachnae were collected by Giard (1896) in September, and he held them in a heated room until the following July, at which time many of the parasitoids were still in the mature larval or pupal stages.

 

The sex ratio generally shows a preponderance of females.  All species of Melittobia that have been studied show females predominating in the ratio of 9:1 or greater, the extreme being 31:1 in M. hawaiiensis when developing on hymenopterous larvae. T. crassinervis and Tetrastichus sp. from elm leaf beetle eggs in Japan are the only species where the sex ratio is circa 50:50.

 

Unisexual reproduction has been found in T. asparagi, Thripoctenus russelli, Ootetrastichus beatus and Thripoctenus brui.  In the case of the latter, both sexes were present with females predominating 3:1, however (Sakimura 1937).

 

Clausen (1940) details the genus Melittobia because of its interesting behavior.  It was noted that host relationships and habits of this genus were studied in great detail.  In particular M. acasta Wlk. was studied by Howard & Fiske (1911), Graham-Smith (1919), Picard (1923), Balfour-Browne (1922b), and Parker & Thompson (1928).  M. chalybii Ashm. was studied by Buckell (1928) and in detail by Schmieder (1933, 1938).  M. acasta is recorded for a variety of hosts and may be either primary of hyperparasitic.  As a primary external parasitoid, it has been recorded from many Hymenoptera, in particular Apoidea, and also from Vespoidea, Sphecoidea, etc.  As a hyperparasitoid, it attacks Ichneumonoidea, Chalcidoidea and Tachinidae.  It has been reared experimentally on a number of hosts not attacked under natural conditions, such as Coleoptera and Lepidoptera pupae and spiders (Parker & Thompson 1928).  In Camponotus pupae development is made possible by partial desiccation, which results in the formation of internal air cavities which simulate natural conditions for the parasitoid.  Oviposition does not occur in Diptera prior to the hardening of the puparium.

 

Sexual dimorphism is pronounced among adults of M. acasta.  Females are normal, with all appendages and organs fully developed, but males are apterous and without eyes.  The males normally do not leave the cell, cocoon or puparium in which they develop, however.  They transform a few days prior to the females and mate with them after the pupal skin is cast.  These males fight among themselves until only one remains alive.  No feeding has been observed in such males, but females feed extensively on body fluids of the host and are able to construct a feeding tube for this purpose if necessary.  Such feeding does not affect the host sufficiently to interfere with later development of the parasitoids.

 

During oviposition the ovipositor may be thrust through the host envelope, of if this is thin, the female may bite a hole and enter the cell of the host larva.  Only mature larvae of Hymenoptera are attacked, being usually stung into immobility prior to oviposition.  Picard reported that the host larvae are killed by the sting, and they may remain in a suitable conditions for feeding by the parasitoid for 8-9 months.  Parker & Thompson found that form and color have no significance as oviposition stimuli, and false cocoons that bear the host blood do not attract the parasitoids.  The number of eggs laid on a host is influenced by its size.

 

Females predominate with males representing only 1-5% .  Virgin females deposit less eggs than mated, which is about equal to the total number of male progeny in a normal brood.  No further oviposition occurs until mating is finished, and this may be on occasion with one of the female's own male progeny from the small number of eggs already laid.  Unmated females take a strong interest in these few developing progeny, frequently stroking them with the antennae, and her interest increases as the pupal stage is reached.  No other instance of maternal care or interest in the progeny is known among Chalcidoidea (Clausen 1940/1962).  An average of 35.6 eggs were secured from each unmated female of a series, the total period extending to 225 days; but this large number was induced by the removal of eggs as soon as they were laid (Balfour-Browne 1922b).  Even if the virgin female has her abdomen distended with eggs, she refuses to deposit more until she is mated, after which she will immediately deposit the full quota.  This is then over 90% female, but some males are produced.  However, the supply of spermatozoa in the spermatheca is not adequate for the fertilization of the entire quota, and thus repeated mating is necessary.  Because both sexes are produced after mating, it is concluded that the female was able to regulate the sex of her offspring.

 

In M. acasta the reproductive capacity is high, a maximum of 1,086 eggs being recorded from a single female.  However, in this case oviposition was extended over circa three months, and the daily maximum was 31.  Unmated females may live four months or longer, so that there is sufficient time available for the development of a brood of male progeny and for normal oviposition after mating with one of them.  Two to five or more generations can occur each year, and two successive broods may develop on a single host larva.  The cycle from egg to adult is a minimum of 17 days, of which two days are required for incubation of the egg, 8 days for larval development and 7 days for the pupa.  Winter is passed as mature larvae or pupae in the host cell or envelope.

 

Schmieder (1933, 1938) studying M. chalybii, found some departures in habit from those of M. acasta.  Although host preferences were similar, females were found to enter the host cell before it was sealed or to attack the larva before the cocoon was spun.  Adults revealed a polymorphism in form comparable with that in social bees and wasps.  The type form of the male was light brown and it had well developed ocelli and the eyes were represented by a black ocellus like spot on each side.  In the second form the ocelli may be absent or vestigial, the eyes unpigmented, the wings smaller and the body color dark reddish brown.  The type form of the female was brownish black, and the wings were fully formed; the second form was brown in color and had crumpled nonfunctioning wings, the exoskeleton was thinner, the sclerites less distinctly outlined and the abdomen was large and distended on emergence.  The type form completes the cycle from egg to adult in circa 90 days, and adults live for 66-75 days.  By contrast, the cycle of the second form was only 14 days and adults lived only a maximum of 30 days.  The type form females had a gestation period of 11-12 days and might deposit a maximum of 500-800 eggs, while those of the second form oviposited the day of emergence, usually did not feed, and produced only 40-60 eggs.  Virgin females produced up to 10 eggs only, and most of those did not hatch.  Usually two complete broods developed on each host individual, the first consisting of both forms, and the individuals of the second form reached maturity quickly and produced a brood destined to be of the type form, which developed along with the type form survivors of the first brood.

 

Winter is passed in the mature second form larval stage.  The type form ensures the dispersal of the parasitoid, while the second form is for reproduction only.  Experiments showed that only type form females can be produced on a host after a small number of second form larvae have developed on it.  This is explained on a nutritional basis, the food of the second form consisting principally of blood, while that of the following type form comprised a considerable portion of solids.

 

Generally circa 3% of the progeny of mated females are male, and although the proportion is small and is further reduced by combat, practically all females are eventually mated.  According to Schmieder, the sex ratio seems to be an adaptive feature which conserves the food supply of the species for the almost exclusive use of the female sex, the sex which alone serves the dispersal of the species.  Males of this species have been found to be haploid, derived from unfertilized eggs of either mated or virgin females, and this condition is generally lethal, but there is no evidence for the production of biparental males.  A very small proportion of eggs were found to possess parthenogenetic potential (Clausen 1940/1962).

 

Entedontinae.

Taylor (1937) made extensive studies on the biology of this subfamily, with several species of Pleurotropis that are parasitoids of the larvae and pupae of Promecotheca, and of several other genera associated with this host. Pleurotropis parvulus is of interest not only because of its habits but from the point of view of effectiveness in host regulation.  It is a gregarious internal parasitoid of all larval instars and the pupa.  The number of eggs laid in a give host varies directly with size, thus, an average of three is laid in 1st instar larvae, while 17 is the average for 3rd instar larvae, prepupae and pupae.  The minimum number that can reach maturity in the later instars is 5 and a lesser number cannot consume enough of the body contents and thus die.  The reproductive capacity of P. parvulus is low, for large females produce an average of 77 eggs and small ones only circa 20.  Examination of the reproductive system of females of different sizes revealed that small individuals consistently had smaller and fewer ovarioles, which was reflected in a reduced egg capacity.

 

The life cycle is completed in 19-21 says, of which circa 3 days are needed to incubate the egg, and 7, 1, and 9 days, respectively, for the larval, prepupal and pupal stages.  Several species of the genus Pleurotropis develop consistently in the tertiary role (Muesebeck & Dohanian 1927). P. tarsalis Sash., and P. nawaii Ashm. were associated with the gypsy moth and related hosts of Apanteles, and they develop on the various species of secondary parasitoids that attack the larvae of that genus.

 

Bakkendorf (1933) studied a few other species of Entedontinae. Anellaria conomeli Bakk. is an internal parasitoid of the egg of Conomelus limbatus F. during its early larval period, but after consuming the contents of the one egg it emerges and completes its development as a predator.  To accomplish this, it has to bore its way through the stem pith containing the host eggs so that it can reach them.  A total 7-8 may be consumed before maturity.  Taylor  (1937) studied Achrysocharella orientalis Ferr., hyperparasitic on Promecotheca through Pleurotropis and Dimmockia.  This parasitoid develops internally in mature larvae or pupae of primary parasitoids within the dead body of the coleopterous host.  When parasitic in Pleurotropis, its early stages are internal, and it then emerges and, in the last stages, becomes predaceous on the remaining individuals of the group within the hispid skin.  Larvae developing in Dimmockia do not have this external feeding phase.

 

In Achrysocharis promecothecae Ferr., parasitic in eggs of Promecotheca in Java, only eggs which are 10 days old or older, in which embryonic development is advanced, are selected for oviposition.  Sometimes a parasitized egg may hatch, in which case the parasitoid completes its development in the 1st instar larva in the mine.  Adults do not emerge through the exposed portion of the egg capsule, but through the ventral side and through the leaf epidermis.  Howard (1891) described an unusual feature in Chrysocharis singularis How., parasitic on larvae of Lithocolletis in a leaf mine.  The mature larva of the parasitoid builds a series of pillars in a circle about its body, which serve to hold the walls of the mine apart and thus protect the pupa following the molt.  Such pillars may be formed of larval meconium, although they are probably derived from regurgitated material (Clausen 1940).

 

In most species the pupal integument is very heavy and black.  After adult emergence the exuviae retain the pupal form rather than becoming a disassociated mass or being broken into pieces, as is generally found in the Chalcidoidea.  Life cycles are very short, being completed in 15-20 days, of which one half the time is passed in the pupal stage.  Pleurotropis tarsalis requires 28-40 days, of which the pupal stage covers a period of 18-26 days (Clausen 1940).

 

Members of this subfamily usually reproduce bisexually.  In most species females predominate, the sex ratio ranging from 1.6:1 in P. metallicus Nees to 3:1 in P. benefica Gahan (Salt 1931), 2:1 in Achrysocharella orientalis, and 7.4:1 in Achrysocharis promecothecae.  However this can be altered by the host stage attacked.  Females predominate from 1st instar Promecotheca larvae in a ratio of 1.7:1, but from 3rd instar larvae and pupae it is 4.3:1.  Males do occur in every generation.

 

Elachertinae.

The gregarious external parasitoid Euplectrus plathypenae How. was studied by Swezey (1924), R. C. Smith (1927), Wilson (1933) and Vickery (1929).  The species attacks half grown or larger larvae of Noctuidae, in particular Cirphis and Laphygma in North America.  It is readily recognized by the characteristic clusters of closely packed larvae upon the host body (Clausen 1940/62).  Up to 45 parasitoids may develop on a single Laphygma larva.

 

Adults are long lived, beginning to oviposit within a day or two after emergence.  Swezey recorded 213 eggs laid by a single female over two weeks.  Eggs are not laid on the host larvae that are about to molt.  During oviposition, the female stands on the body of the host, usually on the dorsum of the thorax or of the first two abdominal segments, and the eggs are placed in groups unevenly spaced, and at times in rows upon the integument, to which they are attached.  Hosts are not paralyzed at oviposition, which leaves a chance for the female to be dislodged during oviposition and of the young larvae being injured while the host is active.

 

Eggs are white when first laid but change to brownish black or black as incubation ensues.  Hatching takes place in circa 2 days and is accomplished by a longitudinal splitting of the chorion along the median dorsal line.  Feeding begins immediately, and the body gradually enlarges and emerges from the egg shell.  The shell remains on a ventral pad, which attaches the larva to the host, and to it the different exuviae are added.  Larvae may not be contiguous in early stages, but as they grow they become very crowded, causing a noticeable compressing of the anterior portions of the body, and the individuals in the center of the group are forced into a vertical position.  According to Smith (1927) the host larva dies at the time eggs hatch, while Swezey (1924) & Wilson (1933) noted that the parasitoid larva may complete feeding before death of the host.

 

The host's body contents are almost completely sucked out and the parasitoid larvae after completing feeding, leave their position on the dorsum, finding their way beneath the host, where they arrange themselves transversely and spin delicate cocoons within which pupation occurs.  Clausen (1940) thought that they are improperly termed cocoons because they are merely thin webs of silken strands which fasten the ribbon-like host integument to the leaf surface and partition off the pupae from their neighbors.

 

The life cycle is short, from 10-15 days in summer, with the egg, larval and pupal stages taking 2, 4-6 and 4-7 days, respectively.  Wilson recorded a sex ratio of 1.5:1 in the third brood and 9.2:1 in the 6th brood.

 

Observations on E. comstocki How., parasitic on cotton leaf worm, by Schwartz (1881) indicate that its habits are similar to those of E. plathypenae.  The host is attacked in an early stage, when it is less than 1/3rd grown, and eggs are placed on the middle of the back rather than on the thorax. E. bicolor Swed. in Europe, attacking caterpillars of a large number of species, was studied by Silvestri (1910c), Thomsen (1928) and Bischoff (1929).  Silvestri found the number of eggs placed on an individual host varied directly with the size of the host.  Oviposition was rapid and eggs were placed at 1 mm intervals on the dorsum between the mesothorax and the 4th abdominal segment.

 

Noble (1938a) gave a detailed account of Australian E. agaristae Cwf., parasitic on caterpillars of the grape vine moth, Phalaenoides glycine Lew.  A maximum of 60 may attain maturity on a single host, although the average is circa 18.  In superparasitism all individuals of the brood continue feeding without combat until the food supply is gone, following which all may die or develop into dwarfed adults.  Winter is thought to be passed as adults, and mated females survived for six months in the insectary.

 

Elachertus differs considerably from Euplectrus.  One species studied by Tothill et al. (1930) is a solitary external parasitoid of caterpillars of Artona trisignata in Java.  The female frequently feeds on the host body fluids, which kills the host.  During stinging a fluid is pumped into the host by the female which causes a marked distention.  The ovipositor remains inserted for 10 min. or more following which the female bites a hole in the integument of the thorax and sucks out body fluids.  The single egg is placed dorsally between the 1st and 2nd abdominal segments.  Just after hatching the young larva moves to the ventral side of the host body and takes up its feeding position between the thoracic and abdominal legs.  If more than one egg is laid on a host, hatching of one causes immediate cessation of development of the rest.  Tothill et al (1930) stated that "Apparently the young larva injects into the host some fluid which is toxic to the other eggs, and this fluid then reaches the latter by diffusion through the egg stalks."  This explanation has been given for the death of surplus individuals among internal parasitoids and is plausible in those species showing appreciable growth of the egg during incubation as a result of imbibing fluids from the surrounding medium.  However, in Elachertus only the pedicel of the egg is within the host body, and this, unless it comprises the micropylar area, which is not probable, would not provide a channel through which diffusion might take place.  The host is temporarily paralyzed at the time of oviposition, and its activities cease completely when the egg hatches.  Liquefaction of the body contents begins immediately and is thought to be due to the injection of some fluid into the body by the parasitoid larva.  If so, the effect is in contrast to the preservative action of the fluids injected by the sting of many other parasitoids and thus this injection is for an opposite purpose (Clausen 1940).

 

Silvestri (1910c) studied Elachertus affinis Masi, a European parasitoid of the mature larva of Polychrosis ambiguella.  Eggs (5-10) are placed within the host cocoon but not directly on the larva, and the latter is not paralyzed.  Young larvae are very active and able to move about freely in the cocoon.  The life cycle takes 11-13 days in summer.

 

Trichospilus pupivora Ferr. differs from the genera already discussed in being gregarious and internal on pupae of the palm caterpillar, Nephantis serinopa Meyr. in India (Anantarayanan 1934).  An average of 55 eggs is laid in each pupa, and a maximum of 211 individuals was reared from a single host (Clausen 1940/62).

 

Euplectrus has interesting pupation habits.  When the larvae finish feeding on the host and have completely sucked out the fluid contents, they leave the dorsal position and seek the underside of the deflated host, where they arrange themselves transversely, in a single orderly row in some cases, and prepare to pupate.  A light weblike cocoon is formed which binds the host remains to the leaf, the latter thus serving as a protective covering.  Several authors have called attention to the fact that the material from which the cocoon is spun is derived from the Malpighian tubules rather than from the salivary glands and that the slender tapering tip of the abdomen of the larva serves as an "arm" in the construction.  The meconium is cast by the prepupa, and sometimes it is ejected from the cocoon.  The pupa lies upon its dorsum and is attached to the substrate by means of the last larval exuvium, which envelops the tip of the abdomen.

 

Tothill et al. (1930) found that the solitary larva of Elachertus sp. similarly pupates beneath the host skin, and the pupa lies on its back with spiracular processes directed upward.  Such "hooks" were considered to serve for protection in holding the host remains away from the body to permit normal respiration.  The collapsed host remains enveloped the pupa closely, and the spiracles at the tips of the hooks were believed to be the only ones that function.  According to Howard (1891), pupae of Elachertus cacoeciae How. are attached by the tip of the abdomen to the silk spun in the leaf roll by host Archips rosaceana Harr., while those of E. spilosomatis How. are found in a group among the long hairs on the dorsum of the abdomen of Diacrisia virginica F. larvae.

 

 

 

Immature Stages of Eulophidae

 

The eggs of the great majority of Eulophidae are simple; they are oblong or oval to elongate, are often slightly arched, and have both poles smoothly rounded.  The chorion is usually delicate and unsculptured, though in Microplectron fuscipennis it shows, under high magnification, minute, conical projections.  In a number of species, the micropyle is distinguishable as a small thickened area at the anterior end.

 

The eggs of several genera of Elachertinae differ from those of the majority of the members of the family.  Those of Euplectrus and Elachertus have been stated by several authors to have a pedicel at the middle of the mid-ventral curve; this serves as an anchor in the skin of the host in the same manner as with the pedicellate eggs of other groups.  Observations regarding its form and origin are incomplete.  In the figure given by Silvestri for Euplectrus bicolor, the pedicel appears to be a definite adaptive modification possibly comparable to that of the tryphonine Ichneu­monidae, and Tothill stated that it is "continuous with the egg shell" in Elachertus sp.  It may prove, however, to be similar in origin to those of Euxanthellus and the male eggs of some Coccophagus, in which a fold of the unmodified chorion is knotted or twisted at the time of deposition and is inserted into the puncture in the host skin.  An examination of the ovarian egg would probably clarify this point.

 

The pronounced darkening of the chorion of the egg during incubation, which occurs in Euplectrus plathypenae and E.  comrstocki, has not been observed in other species of the family. Records of the number of larval instars of the different species show little consist­ency.  Only three have been detected in Eulophus viridulus and Melittobia acasta, four in Pleurotropis parvulus, Tetrastichus ovivorax and Euplectrus bicolor and five in Microplectron fuscipennis.

 

The first instar larvae are hymenopteriform and somewhat cylindrical, with 13 distinct body segments, and they have no characters to distinguish them readily from larvae of related families.  Occasional species bear fleshy protuberances or tubercles on the body.  In Diaulinus sp. (Solenotus sp.) figured by Parker (1924), the sensory setae are borne upon distinct tubercles.  The larvae of Dimmockia javana possess distinct intersegmental protuberances, which function as pseudopodia, on the mid­ ventral line from the second to the ninth body segments.  Each segment bears a transverse row of minute setae on the dorsum and sides near the posterior margin.  The last abdominal segment is bifurcate in Tetrastichus sp. (Berry, 1938); this species has been confused with T. xanthomelaenae from the same host, but the latter does not possess this character. Melittobia acasta has a row of minute spines at the anterior margin of each segment, and T. taylori has a double row in the same position.  In T. avivorax, this row of spines occurs only dorsally on each segment except the first and in the Tetrastichus sp. mentioned above they encircle the segments.  Accord­ing to Silvestri (1910c), the row of spines occurs at the posterior margin of the segments in T xanthomelaenae. P.  parvulus apparently lacks the sensory setae and cuticular spines.

 

The integument of a number of species bears a distinct sculpturing.  That of T. ovivorax has a pebbled appearance, whereas in T. xanthomelaenae it is imbricated. Hyperteles intermedia Thoms. (Parker and Thompson, 1928) has irregular areas of minute tubercles on all body segments except the last two.  There are three pairs of sensory tubercles on each thoracic segment and four pairs on each abdominal segment except the last, which has only one.

 

The majority of species that have been studied have an open tracheal system, with spiracles on the mesothorax and the first three abdominal segments.  Euplectrus bicolor is said to have five pairs, the additional one being on the metathorax.  Several species of endophagous habit lack the open tracheal system, among them being P. parvulus, Tetrastichus taylori, Anellaria conomeli and Thripoctnus bruni.

 

The distinguishing characters of the first instar, particularly the cuticular spines and ornamentation, usually do not persist after the first molt, and the intermediate larval instars of the different species are consequently quite similar.  In Diaulinus, however, the tubercles and setae are retained to the final instar, and this is true, also, of the two pairs of "papillae" on the last abdominal segment of Eulophus viridulus.  In most species, the full complement of nine pairs of spiracles, situated on the last two thoracic and the first seven abdominal segments, appears in the second instar.  They are stated to be on the mesothorax and the first eight abdominal segments of Melittooia acasta.

 

The mature larvae are usually of simple form, with very few integumentary spines or setae, and are usually without surface sculpturing. Tetrastichus eriophyes bears transverse striations, whereas T. ovivorax has the minute tubercles, mentioned for the first instar, ventrally.  The larva of H. intermedia bears numerous small integumentary tubercles in transverse rows both ventrally and dorsally on all body segments except the last.  In Thripoctenus brui, the mature larva differs considerably from that of other genera in being cylindrical and about three times longer than wide, with both ends broadly rounded and no visible segmentation; it bears a transverse ring of about 12 short but stout spines at the middle of the body.  The mandibles of Tetrastichus ovivorax bidentate, in contrast to the simple form of other species of the family.

 

The larvae of the gregarious species, such as Euplectrus upon free living hosts, are pear shaped and are very broad in the mid abdominal region; the last four or five segments are much narrowed.

 

Nine pairs of spiracles are usually present, these being on the last two thoracic and the following seven abdominal segments. Pleurotropis benefica, P. parvulus and Chrysocharis laricinellae Ratz.  larvae only seven, those on the third thoracic and on the first abdominal segments being missing.  In P. parvulus the number is said to be variable, usually smaller than the full complement mentioned, and it may differ on the two sides of the same individual. Thripoctenus brui and Anellaria conomeli lack the spiracles even in the mature larva, and Silvestri did not mention or figure them in Tetrastichus ovivorax.

 

The pupae of a considerable number of species, particularly of the Eulophinae, have an exceptionally heavy integument which may be jet black or dark brown in color.  In a species of Elachertus found attacking Altona by Tothill, the pupa bears a pair of fleshy processes at the lateroventral margins of the seventh and eighth abdom­inal segments, each of which bears a spiracle at its tip.