HYMENOPTERA, Ichneumonidae (Leach 1817) - (Ichneumonoidea) -- <Overview>
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This is one of the largest groups of parasitic insects. It probably ranks first in effectiveness of reducing or holding in balance numerous phytophagous pests. Dominant families are Ichneumonidae and Braconidae (Clausen 1940). In this section the families Agriotypidae, Aphidiidae, Apozygidae, Braconidae, Ichneumonidae and Paxylommatidae will be treated separately in the respective files <agriop.htm>, <aphidid.htm>, <apozygid.htm>, <braconid.htm>, <ichneu.htm>, & <paxylom.htm> [Also see taxnames for more details].
Ichneumonidae. -- The ichneumonids are one of the most important parasitic insect groups and also one of the largest in the Insecta. There have been over 3400 species found in North America alone. The adults vary in size, form, and coloration, but most resemble slender wasps. They have a long, narrowed appearance, and there is a large stigma on the forewing. They differ from the stinging wasps by having antennae that are longer and with more segments. Their trochanters are 2-segmented (1- segmented in the stinging wasps), and they a costal cell in the front wings is absent.
The ovipositor can inject eggs into the host, which may be another ecto- or endoparasitoid. In many species the ovipositor is quite long, often longer than the body, arising anteriorly to the tip of the abdomen being permanently extended. In the stinging wasps the ovipositor issues from the tip of the abdomen and is withdrawn into the abdomen when not being used. The ichneumonids differ from the braconids by having two recurrent veins whereas the braconids have only one or none and in having an abdomen that is longer than the head and thorax combined. In many species there is a considerable difference in the appearance between males and females.
The ichneumons attack a variety of hosts, though most species attack only few kinds. There are few groups of insects that are not hosts of some ichneumonid, and some species in this family attack spiders. Most ichneumonids are internal parasitoids of the immature stages of their hosts. The parasitoid may complete its development in the stage of the host in which the egg is laid or in some later stage.
This is a large family with many species, and the adults vary greatly in size, form and color. Ichneumonidae include some of the most conspicuous forms among the parasitic Hymenoptera, notable among which are the species of Rhyssa and Megarhyssa of the tribe Rhyssini (Clausen 1940/162). Members of this group are parasitic on the larger wood-boring Hymenoptera and are conspicuous because of the extreme length of the ovipositor. The female of one unnamed ichneumonid from Peru was figured by Bischoff (1927) to be 15.0 cm in length as compared with a body length of only 2.0 cm.
A majority of species has fully developed wings and is very active in flight, but some species, particularly of the cyrptine genus Gelis, have apterous females and the males may be either winged or apterous. Muesebeck & Dohanian (1927) believed that the males of G. apantelis Cush. G. nocuus Cush., and G. inutilis Cush. were always winged, while both forms are found in G. urbanus Brues and G. bucculatricis Ashm. There is no regularity in the appearance of either form, and virgin as well as mated females produce both. Thompson (1923a) found intermediate forms, with the wings in various stages of reduction in G. sericeus Foerst. The production of both winged and apterous individuals of the same sex is considered to be due possibly to a difference in the quantity of food material available to the individual larvae. In Hemiteles hemipterus F. both sexes of which are alate, there is a marked variation in wing size among the females, some having wings only half as long as other, and with a modified venation.
Ichneumonids have been imported into a number of countries and colonized in infestations of lepidopterous and other pests, as a biological pest control tactic. However, the results have not been as satisfactory as with other parasitic groups, and Clausen (1940/1962) knew of only two instances where pronounced benefits were obtained. Bathyplectes curculionis Thoms., imported from Italy, contributed to the biological control of alfalfa weevil, Hypera variabilis L., in the United States; and Mesoleius tenthredinis Morley, imported into Canada from England, is credited with a major part of the control of the larch sawfly, Lygaeonematus erichsoni Htg. (Clausen 1940/1962).
Most species of ichneumonids are primary parasitoids and many exert a pronounced effect on the host population. Because of the large number that have been studied and the great range in host preferences, the principal subfamilies are discussed separately, with particular reference to the principal tribes and genera where a uniformity of preference is shown within these lower groups (Clausen 1940/1962).
Species of the subfamily Joppinae are consistent in their host preferences and are recorded only as internal parasitoids of the larvae and pupae of Lepidoptera. In the species attacking the larva, emergence of the adult is from the pupa. The dominant genus is Amblyteles, which is distributed worldwide, and is represented by a very large number of species.
Cryptinae are external parasitoids of a very wide range of host groups, although the tribe Cryptini contains many species that are internal parasitoids. As primary parasitoids, members of this subfamily attack lepidopterous larvae most frequently, although a few species are known to develop on sawfly and coleopterous larvae, and an occasional species on the pupae of Trichoptera and Diptera. Many species of the genus Gelis (Pezomachus) are predaceous on spider eggs and young spiders in the egg sacs. Salt (1931b) studying the habits of Hemiteles hemipterus, found a seemingly obligatory alternation of generations. The females reared from larvae of the wheat stem sawfly, Cephus pygmaeus L. during May and early June refuse to oviposit in this host but readily accept others. Under field conditions, Cephus larvae are not available until the end of August, so that there is ample time for the development of a midsummer brood upon some host as yet unknown (Clausen 1940/1962). The autumn brood of Xylophruridea agrili Vier. develops on the mature larvae of Agrilus, while the spring brood attacks the pupae of the same host species (Clausen 1940/1962).
Habrocryptus graenicheri Vier. (Graenicher 1905a), developing at the expense of the egg and larval instars of Ceratina dupla Say, is of unusual habit in that the host stages contained in 3-4 cells may constitute the food of a single larva.
Hyperparasitic habits are strong in this subfamily. Many species of Gelis attack the larvae in the exposed cocoons of various Braconidae, especially the Microgasterinae, and in those of other Ichneumonidae. The genus Hemiteles also contains many species that are either obligate secondary parasitoids or are able to develop in either the primary or the secondary role. H. hemipterus, already mentioned, may possibly develop in the latter capacity in its midsummer generation. The larvae of Spilocryptus ferrieri Faure and a variety of S. migrator F. are predaceous on those of Pteromalus variabilis Ratz. in the pupae of the cabbage butterfly (Faure 1926).
Ichneumoninae are a large group with varied host preferences, although the greater number of species probably are internal or external parasitoids of lepidopterous, coleopterous and hymenopterous larvae, particularly the wood- and stem-boring forms, and a considerable number attack lepidopterous pupae. Many of the species of the Ephialtini are distinguished by an exceptionally wide host range, some attacking a large number of Lepidoptera and also including Coleoptera and Hymenoptera among their hosts (Clausen 1940/1962). The most commonly found genera of the subfamily are Lissonota, Glypta, Ephialtes and Scambus. The members of the Rhyssini are external parasitoids of hymenopterous larvae of the phytophagous families Xiphidriidae and Siricidae. Records of members of this tribe attacking coleopterous larvae ar questionable (Clausen 1940/1962). A considerable number of species are external parasitoids of spiders, and the genus Polysphincta is known to be limited to such hosts. Tromatobia and Zaglyptus develop as predators in spider egg sacs, although Z. variipes Grav. is reported to develop as a parasitoid of the adult spiders themselves (Maneval 1936). The larvae of this species not only suck the fluid contents of the dead spiders but consistently feed on the eggs in the nest (Nielsen 1935). Species of genera Grotea, Macrogrotea, and Echthropsis develop at the expense of bees and have the habit of destroying the egg or young larva in the cell and then completing their feeding on the beebread with which the cell is provisioned (Clausen 1940/1962).
The subfamily Tryphoninae contains predominantly solitary parasitoids of the larvae of sawflies, though a few species attack lepidopterous larvae and pupae and dipterous larvae. The sawfly parasitoids are contained in the tribes Catoglyptini, Ctenescini, and Tryphonini, while those attacking caterpillars are largely in the Paniscini, of which the most frequently encountered genus is Paniscus. The species of the genus Sphecophaga, of the first-named tribe, are parasitic in the larvae and pupae of Vespa. The Ctenescini, Tryphonini, and Paniscini are external parasitoids. The Diplazonini, represented principally by Diplazon, Syrphoctonus, and Homotropus, are internal parasitoids of Diptera, especially the Syrphidae, and the less common Exochini and Metopiini develop internally in lepidopterous pupae. Hypamblys albopictus Grav. is an internal parasitoid of nematus larvae, and Oocenteter tomostethi Cush. develops similarly in larvae of Tomostethus.
Ophioninae are recorded as internal parasitoids only, and the great majority of species, included mainly in the tribes Ophionini, Campoplegini, and Cremastini, develop at the expense of lepidopterous larvae. However, in the Ophionini several species of Ophion are known to depart from the general habit of the group and are internal parasitoids of scarabaeid grubs in the soil. The species of the genus Bathyplectes, of the Campoplegini, are probably limited to curculionid larvae, while Holocremnus and Olesicampe attack sawfly larvae. Most of the Therionini and Banchini attack lepidopterous pupae. The Porizonini are of varied habit, with Orthopelma parasitic in cynipoid larvae and Thersilochus in those of certain Curculionidae. The hyperparasitic habit is strongly developed in the Mesochorini, of which the most frequently encountered genus Mesochorus attacks the larvae of Braconidae and of other Ichneumonidae (Clausen 1940/1962).
Ichneumonidae present a number of biological and behavioral features of special interest. Because of the abundance of species, their wide distribution, and their importance in natural control of many leading crop pests, they have been extensively studied and a vast literature is available regarding them. Cushman (1926b) gave an account of the principal types of parasitism found in the family, with illustrations of the various modifications in the egg and larval forms. He distinguished four types of external parasitism, of which the first, exemplified by the Rhyssini and Ichneumonini, is the least specialized and most common. The egg is simple in form and is deposited upon or near the host, which is enclosed in a cocoon, feeding burrow, or pupal shell or is otherwise enveloped. The host may be permanently paralyzed or killed by the parasitoid sting, or it may not be stung (Clausen 1940/1962).
The second type includes the Polysphinctini parasitic on spiders, in which the host is temporarily paralyzed and the firmly fixed eggshell is utilized by the developing larva as a means of maintaining its attachment to the host body. The third type is similar to the second, but the egg is provided with a pedicel which is inserted through a puncture in the host skin. The species of Paniscini, Tryphonini and Lysiognathinae are of this type, and attack is upon free-living caterpillars and sawfly larvae.
The fourth type, shown by Grotea and related genera, differs from the first in that the egg or young larva of the bee host is first consumed and further development is on the plant materials with which the cell is provisioned.
Cushman additionally distinguishes five types of internal parasitism which are not as well defined as the external forms. These represent a progressive specialization, principally in larval forms and habits.
There is much variation in the reproductive system of the females of the several groups of the family as a result of the different types of eggs deposited and the manner and place of oviposition. Pampel (1914) gave a very extended and illustrated account of the female reproductive organs and the eggs of a large series of species, representing all the principal subfamilies, and he found that they are of four distinct types. The most highly specialized of these is designated the tryphon type, illustrated by the Tryphoninae, in which uterine incubation may take place and the egg is equipped with a pedicel that permits of its being carried on the ovipositor and partially embedded in the skin of the host when deposited. Among the species of Tachinidae that incubate the eggs before deposition, the posterior uterus is thick-walled and abundantly provided with tracheae, forming a distinct incubating organ; but such an adaptation seems lacking in the Tryphoninae, and it may be unnecessary because of the small number of eggs that can be contained in the uterus at any one time (Clausen 1940/1962).
The Ophion type of reproductive apparatus is similar to the above, but the number of ovarioles is large, totaling 30-80, and the eggs are much smaller. The oviducts are often longer than the ovaries themselves.
In the borer type, represented by Ephialtes and Rhyssa, the number of ovarioles is only 8-12, and these are very long and the stalked eggs, of which there are only two or three in each, extend almost the entire length. The ovipositor is very slender, to permit penetration of bark, etc., and the stalked form of the egg allows it to pass through a very narrow channel (Clausen 1940/1962).
The Ichneumon type of reproductive apparatus consists of a small number of long ovarioles, each containing three or four eggs, of which only one is mature, and only the basal third of each ovariole contains eggs. The oviduct is short and the uterus short and flattened. Mature eggs are large and unstalked (Clausen 1940/1962).
Adult Habits.--A preoviposition period has been determined for only a few species and appears variable. Nemeritis canescens Grav. was reported to be able to deposit eggs the day of adult emergence (Daviault 1930), while Glypta rufiscutellaris Cress. does so in 2-6 days (Crawford 1933) and Exeristes roborator F. in 5-10 days (Fox 1927). In Ephialtes extensor Tasch. (Rosenberg 1934), the period elapsing between emergence and first oviposition is 10-19 days at 25°C. and 20-30 days at outdoor temperatures during the early part of the year. Cushman (1913b), dealing presumably with this species (given as Calliephialtes sp.), mentioned a gestation period of ca. 9 days. Phaeogenes nigridens Wesm. requires ca. 11 days at 25°C., but this period is greatly extended at lower temperatures, being ca. on month at 18°C. and three months at 8°C.
Adult life in the majority of species covers ca. 6-8 weeks, the period thus being much longer than in the Braconidae. Those which hibernate in the adult stage naturally are adapted for a long life, and adults of P. nigridens have been kept alive as long as 10 months in the laboratory (Clausen 1940/1962).
The stimuli that induce oviposition by the female are varied and are related more or less directly to the habits of the host stages attacked. In free-living larvae, the host body itself provides the stimulus; but where larvae or pupae in tunnels or cocoons are attacked preliminary direct contact is not possible. In Pimpla instigator F., odor seems to be the inciting agency, and a great activity by the females is induced by fresh host blood (Picard 1921). Actual deposition of the egg, however, requires tactile responses through organs on the ovipositor. In host stages contained in a cocoon, it is often the cocoon that provides the stimulus, while with larvae boring in stems, fruit, etc., it is often the frass that accumulates at the entrance to the burrow. Most species that parasitize protected host stages show no interest in them when they are removed from the tunnel or cocoon. In Spilocryptus extrematis Cress, the cecropia cocoon seems to provide a necessary stimulus, for free larvae are never attacked (Marsh, 1937). Females are attracted in large numbers as soon as the larvae begin spinning, this being an obvious olfactory response. In one case 34 females oviposited in a single cocoon at the same time, with a total of 1,011 eggs found. Cushman (1916) found that the oviposition scar of Conotrachelus seems to provide the necessary stimulus for Thersilochus conotracheli Riley, and he found that females would frequently attempt to insert their ovipositors in abrasions in the skin of plum fruits, whether or not they were infested with curculio larvae.
The majority of Ichneumonidae oviposit directly on or in the host stage on which the larva is to complete its development, although many attack the host in its larval stage and emerge from the pupa. The firs record of an ichneumonid species ovipositing in the egg of its host is that by Kurdjumov in 1915, who found that Collyria calcitrator Grav. does so but does not complete its larval development until the host larva is nearly mature. More recently Cushman (1935) found Oocenteter tomostethi to place its eggs in that of the sawfly host and the latter attains larval maturity and spins its cocoon before death. Sagaritis dubitatus Cress. was reported to place its egg in the host embryo immediately before hatching, but other investigators questioned this observation and stated that oviposition is only in late 1st or early 2nd instar armyworms (Clausen 1940/1962).
Oviposition habits in Diplazon laetatorius F., particularly as they pertain to the stage of the syrphid host attacked, are of special interest. The egg may be placed in either the egg or the larva, and the adult parasitoid emerges from the puparium. Oviposition in eggs of Baccha was observed by Kelly (1914b), and he secured the adults from the puparia of those individuals. Later researchers found that oviposition takes place in eggs only when the embryo is fully developed and that young larvae are also attacked. Kamal (1939) found that the 1st and 2nd larval instars are preferred for oviposition. On the other hand, Bhatia (1938) reported that D. tetragonus Thbg. oviposited only in 3rd instar larvae.
Eggs of larval parasitoids that oviposit in the eggs of the host are usually of minute size, but Diplazon is a conspicuous exception to this rule. That of a species in Japan, which was listed as D. laetatorius F., measures 0.65 mm. in length and 0.14 mm. in width and is forced into a syrphid egg only 1.0 X 0.35 mm. The distention of the host egg thus produced is often so great as to break the waxy incrustation that covers it, and it is remarkable that the host embryo is able to complete its development and the larva to hatch normally with so large an egg within its body (Clausen 1940/1962).
Most species of Ichneumonidae that develop internally in the host place the egg at random in the body cavity, although the eggs have a tendency to move with the blood stream and they frequently lodge at the posterior end of the abdomen. However, Heteropelma calcator Wesm. inserts the ovipositor through the mouth or the anal opening, and the egg is fixed to the thin lining of the terminal portions of the alimentary canal. Only in Amblyteles subfuscus Cress. is the egg position known to be confined to a single organ, and in this case it is always in the salivary gland (Strickland, 1923).
External parasitoids attacking larvae in cocoons, galleries or leaf-rolls place the egg on any part of the body of the host or loosely nearby. That of Grotea anguina Cress. is placed longitudinally on the egg of the host in its cell. Females of Pimpla macrocerus Spin., which attack mature larvae of Odynerus in a hard-walled cell, secrete a drop of fluid at the tip of the ovipositor, which serves to soften the wall and thus facilitate penetration (Janvier 1933). The egg is attached to the interior of the wall of the cell, and at hatching the young larva drops to the body of the host.
Most species of the Tryphonini and Paniscini are of unusual habit in that they attack free-living host larvae which continue their feeding after parasitization. The species of Paniscus and Phytodictus that have been studied place the egg in an intersegmental groove between two thoracic segments or between the thorax and the abdomen. Tryphon incestus usually inserts the pedicel of the egg in the neck of the host larva, either dorsally or laterally, while Lysiognatha seems to attach it more often to the head. Several other species of this subfamily attach the eggs at the side of the body, usually on the thorax or anterior abdominal segments, but Exenterus coreensis Uch. consistently places it transversely on the median dorsal line of the 2nd thoracic segment.
Most Polysphincta and other genera of spider parasitoids place the egg dorsally or laterally at the base of the spider abdomen, though a few are known to deposit it on the posterior declivity of the cephalothorax. The latter is the normal habit of Schizopyga podagrica Grav. The female of Zaglyptus variipes, however, kills the female spider in her nest and then deposits 1-8 eggs upon the freshly formed egg "cocoon" (Nielsen 1935).
The species of Mesochorus which develop in braconid and ichneumonid larvae are indirect in their relationship, for oviposition takes place in the body of the primary host while the latter is still contained in the living caterpillar. A similar habit is recorded for Stictopisthus javensis Ferr., attacking Euphorus larvae in Helopeltis in Java.
Ectoparasitic Tryphoninae oviposit differently in several ways from that by other groups of similar habit. Even though free-living larvae of considerable size are attacked, many species do not even momentarily paralyze them. However, several species of Paniscus accomplish this by an insertion of the sting in the thoracic region prior to that which results in egg deposition. The female of Tryphon incestus springs on the sawfly host from the rear and inserts the egg pedicel in the neck by a very rapid thrust of the ovipositor. Chewyreuv (1912) described in detail the manner of oviposition of two species of Paniscus, observing that some eggs were deposited on host caterpillars which were still active, while others were on completely, though temporarily, paralyzed hosts.
All species that have the pedicellate type of egg hold only the pedicel or anchor within the channel of the ovipositor, and the main body issues ventrally at the base of the ovipositor right after it leaves the oviduct. Because of its large size and heavy inelastic chorion, the egg could not be compressed sufficiently to permit its passage through the ovipositor channel (Clausen 1940/1962).
Species attacking wood-boring larvae must penetrate considerable depth of wood to oviposit, and have attained an extreme length of this organ. This requires an involved process of manipulation to attain the required position for drilling and to exert the force necessary for penetration. Riley (1888) gave an extended account of the manner of oviposition of Megarhyssa lunator F. In this species the hind legs are used to bring the ovipositor into a vertical position. The sheaths of Megarhyssa are arched dorsally over the abdomen and serve to guide the ovipositor proper, but they do not penetrate the wood. In the early phases of the act, the forcing of the basal portion of the ovipositor into a coil in a membranous intersegmental "sac" between two of the abdominal segments permits the terminal portion to be brought into a perpendicular position for the beginning of the drilling process. This provision for manipulating an ovipositor of exceptional length is also found in Leucospis in the Chalcidoidea. Abbot (1934) described in detail the mechanics of oviposition, and Cheeseman 91922) described the oviposition of Rhyssa persuasoria L., and Brocher (1926) discussed the manner in which it was accomplished by Perithous mediator Grav.
Several researchers asserted that Megarhyssa drills at times through solid wood to reach the host for oviposition, but this is questioned by Abbott, who found that cracks, crevices, etc., were utilized to teach the host burrow and that the only real drilling which took place was through the bark. The parasitoid may possibly utilize the oviposition holes previously made by Tremex. However, some workers have observed that R. persuasoria can at times penetrate solid wood.
Rosenberg ( ) referred to an interesting point in Ephialtes extensor. Eggs that are deposited during the latter portion of the oviposition period of the female were consistently different from those first laid, being markedly wider in relation to the length. A portion of the eggs of this species are devoid of contents when laid, and the number of these is greater after a period of rapid oviposition and during the latter portion of the oviposition period of the female.
Chewyreuv (1912) called attention to the habit of the females of many Ichneumonidae of dropping their eggs at random when hosts are not available. This was true mostly among ectoparasitic species and was thought to be due to the necessity of eliminating the mature eggs in the oviduct to make way for others that were developed, and also to avoid injury to the internal organs of the parent. Such action is disadvantageous to the parasitoid, for it involves the loss of these eggs. H. D. Smith (1932) noted that no eggs were ever found in the oviduct of Phaeogenes nigridens Wesm. and that those which mature in the follicles soon disintegrate and pass out through the oviduct if there is no opportunity for oviposition.
Some Tryphoninae conserve their mature eggs for a time at least, by carrying them externally upon the ovipositor, with only the pedicel held between the blades (Clausen 1940/1962). This habit seems to be quite common in Polyblastus and has been found also in Dyspetes and Tryphon. Pampel ( ) mentioned one female of P. cothurnatus Grav. carrying 17 eggs upon the ovipositor, and T. incestus Holmg. was observed to carry as many as 10. These eggs are large in size and in both bases the number carried was in excess of that which could be held in the uterus. The occurrence of this habit is not correlated with the stage of incubation of the egg, nor is it obligatory. In T. incestus, it was thought that the presence of eggs upon the ovipositor was only accidental, the result of unsuccessful oviposition attempts, in which the act was interrupted between extrusion of the egg and its attachment to the host larva. The eggs carried like that on the ovipositor may eventually be abandoned, or they may be used in later successful ovipositions.
Kerrich (1936) concluded while studying the retention of eggs on the ovipositor by Polyblastus strobilator Thbg., that this is a provision for protection of the progeny. However, there is little evidence that this habit is of any advantage to the parasitoid other than in conserving the eggs during a period when normal oviposition is not possible (Clausen 1940/1962).
Many adult female Ichneumonidae feed on the body fluids of the host stages that they parasitize; this is either incident to oviposition or entirely independent of it. The habit is most general in the Ichneumoninae and the Cryptinae. Polysphincta parva Cress. feeds on the body fluids that exude from ovipositor punctures in the body of the spider host (Cushman 1926). In Ephialtes, Exeristes, and related genera, the feeding may have no relation to oviposition, and the punctures are often enlarged by use of the mandibles. Not only the fluids but the entire body contents may be consumed; and the feeding habit, instead of being incidental to and associated with oviposition, has developed into a distinctly predaceous habit, independent of the reproductive activities, though very probably essential to oögenesis (Clausen 1940/1962). Pimpla instigator, Itoplectis conquisitor Say, and several species of the cryptine genus Hemiteles have the habit of feeding, while the ovipositor is still inserted, upon the host body fluids that rise along the ovipositor by capillary action. H. hemipterus feeds upon the fluids of codling moth larvae, though reproduction takes place only as a secondary parasitoid through Ephialtes. Diplazon laetatorius, which oviposits either in the syrphid egg or young larva, makes an initial insertion of the ovipositor in the egg for exploratory purposes and then applies the mouth parts to the puncture. If the embryo is well developed, the ovipositor is reinserted and the egg laid, but if the egg is till quite fresh the contents are completely sucked out. The number thus consumed may be vastly greater than is utilized for oviposition. No representative of the family is known to construct a feeding tube such as is made by many Braconidae and Chalcidoidea.
Species of Ichneumonidae that attack larvae in cocoons, tunnels, leaf rolls, etc., and whose larvae feed externally usually permanently paralyze their hosts at the time of oviposition. This habit is most common in Ichneumoninae and Cryptinae. Codling moth larva stung by Aenoplex carpocapsae Cush. are thought to remain in a fresh physical condition for a max. of 73 days and an average of 26 days (McClure 1933). Spilocryptus extermatis kills the cecropia larva at the time of oviposition, and the substance injected into the body at the time of stinging exerts a pronounced preservative effect. The larva of Gyrinus, which is the host of Hemiteles hungerfordi Cush., is stung by the parasitoid but is not paralyzed, though it is thought that further development is inhibited. In some species, particularly the genus Exeristes, host larvae are often killed by the sting, and a repetition of stinging frequently results in death of the host in the case of species that normally effect only permanent paralysis. Female Phaeogenes nigridens enters the corn borer tunnel in search of its host, bites away an opening in the cocoon, enters it and then stings the pupa at the base of one of the wing pads (Clausen 1940/1962). Polysphincta paralyzes its spider host temporarily, and P. eximia Schm. is thought to insert its sting in the mouth. In this genus it is probable that the paralyzing agent injected at the time of stinging, rather than the feeding activities of the young larva, is responsible for the inhibition of molting by the host (Clausen 1940/1962).
Development of Eggs & Larvae.--Most species except those of the Tryphoninae, have a relatively short egg incubation period of 1-3 days. Some species have 6-8 days, but in some of these cases the longer period has been observed at low temperatures during the incubation. In some species that deposit their eggs internally, it was observed that there is a considerable increase in size during incubation, although this is not nearly so general nor is the growth so extensive as in the Braconidae (Clausen 1940/1962).
The greatest variation in egg production and incubation is found among the Tryphoninae. Of the endoparasitic species, D. laetatorius hatches in 1-4 days, and Hypamblys albopictus was reported to require ca. 14 days. Among the ectoparasitic forms, there are found the only instances of uterine incubation known among parasitic Hymenoptera, which is in contrast with the frequent occurrence in parasitic Diptera. This habit is normal in some, though not all, species of Paniscus, Polyblastus, and Dyspetes. Complete uterine incubation is seemingly normal in Paniscus cristatus and P. ocellaris Thoms., as judged by the results of dissections reported by Chewyreuv, and several instances were observed in which the death of the parent female resulted from the perforation of the wall of the uterus by the larvae. In most of the cases of uterine incubation, however, it is only partial and is completed while the egg is carried on the ovipositor or after deposition on the host. In the above two species of Paniscus and in Polyblastus strobilator, the anterior portion of the body of the larva is usually found to be extruded from the egg at the time of deposition on the host. Vance (1927) observed that the eggs of Paniscus spinipes Cush. and P. sayi Cush. are in various stages of development when laid, and some of them require a period of external incubation of 6-8 days. This variation is apparently correlated with the availability of hosts, and when these are abundant and other conditions are satisfactory the eggs are deposited rapidly and before appreciable embryonic development has taken place (Clausen 1940/1962).
Observations on species of the genera Tryphon, Exenterus, Anisoctenion, and Polyrhysia revealed that no uterine incubation took place in these forms (Clausen 1932a). The first-instar larva of T. incestus is not fully formed in the egg until 6-8 days after it is laid, and embryonic development of the eggs of T. semirufus Uch. does not progress appreciably so long as the host is active and feeding. In both species actual hatching takes place only after the host has formed its cocoon. The factor responsible for hatching is evidently atmospheric humidity, which has a softening effect on the tough eggshell. Precocious hatching can be readily induced by confining active host larvae bearing eggs in closed containers with foliage, thus resulting in high humidity and in moisture condensation on the surface. Morris et al. (1937) discussing the habits of E. tricolor Roman, pointed to the necessity for delay in hatching until the host cocoon is formed, for otherwise the larvae will inevitably be lost either during the molts intervening between hatching and the cocooning of the host or during the spinning of the cocoon. In the Pasiscini the larvae of which remain firmly anchored in the eggshell, there is because of this habit no need for delayed hatching. Morris (1937) found that the eggs of E. abruptorius often do not hatch until one month or more after deposition.
Hatching in Lysiognatha spp. (Lysiognathinae) is likewise delayed until the formation of the pupal cell of the sawfly host in the soil, which points to the prolongation of the incubation period to as much as two months (Cushman 1926).
Hatching is not uniform for all Tryphonini. In Paniscus the chorion splits longitudinally along the median ventral line and at the front, and the shell then becomes a shield over the dorsum and sides of the posterior segments. The eggs of Tryphon similarly hatch by means of a longitudinal split which extends halfway from the anterior end. In Exenterus and Anisoctenion, which embed the eggs in a wound in the host integument and leave only the dorsum exposed, a different procedure is necessary to accomplish hatching externally. The embryo is U-shaped as it lies within the egg, with the head bent back over the dorsum, and the mouth parts of the larva are consequently in contact with the dorsum of the egg, which makes external emergence possible.
Larvae of a number of groups have the habit of retaining a connection with the eggshell during the greater portion of their development. This requires that the egg itself be firmly attached to the host body. In the Paniscini this is accomplished by a pedicel inserted through a puncture in the integument, which effectively prevents loss at molting. Appreciable larval feeding does not begin until the caterpillar host is full grown and has formed its cocoon or pupation cell. The spined tip of the abdomen of the parasitoid larva is held in the eggshell, and the successive exuviae envelop the posterior end of the body of the older larvae. This connection is usually broken at the beginning of the last larval stage. In Phytodietus segmentator Grav., parasitic on Loxostege in Russia, the connection is maintained even through the last stage (Anisimova 1931). In the Lysiognathinae, the pedicellate eggs of Lysiognatha serve to anchor the larva in the same way. Eggs of Polysphinctini are attached not by a pedicel but instead by a large quantity of mucilaginous material. Molting of the spider host obviates the danger of loss by molting of the spider host by the effect of the sting at the time of oviposition, which usually inhibits transformation to the next stage. The tip of the abdomen of the parasitoid larva remains in the eggshell; as a further aid, the first cast skin adheres firmly to the body of the host, and the later instars are provided with paired fleshy processes on the venter of the abdomen, which are fixed in the exuviae. Each lateral pair apparently serves in pincerlike fashion to hold a fold of the exuviae. Thee are therefore two points of attachment of the larva rather than only one, and this serves a good purpose because the host is free-living and active until the parasitoid attains the last stage of larval development. However, hosts of the Tryphonini and Lysiognathinae are active at the time of oviposition by the parasitoids, but the latter do not grow much until the cocoon or cell is formed and the host is quiescent. Because of this a much less firm attachment is required, and in fact appears unnecessary after the first molt (Clausen 1940/1962).
The encystment of the primary larva of a species of Ichneumonidae is recorded by Plotnikov in the case of Heteropelma calcator. The cyst is said to consist of an outer membrane, lacking nuclei, within which occur large nucleated cells and a cellular protoplasm, and the cyst may originate from the fatty tissues of the host. That it is of host origin is unquestionable, for the egg is deposited in the mouth or in the posterior end of the intestine, and the newly hatched larva consequently has to be an active form capable of penetrating the intestinal wall at one end or the other of the digestive tract. This precludes the possibility of the cyst, which envelops the larva after it reaches the body cavity, being a persistent trophamnion. The winter is passed as a 1st instar larva within the cyst, which breaks down at the beginning of activity in springtime (Clausen 1940/1962).
A "feeding embryo" was discussed by Tothill (1922) in Therion morio F., an internal parasitoid of the larva of Hyphantria. Immediately after hatching of the egg, the larva is found to be enveloped in an embryonic membrane. This membrane, or sac, persists until the 2nd larval stage, and through it the larva derives its liquid food. The essential function of this sac is probably for protection of the parasitoid from the phagocytes of the host during the changes incident to its pupation (Clausen 1940/1962).
In Collyria calcitrator, the 1st instar larva apparently encysts itself for transformation to the following instar (Salt 1913b). This usually takes place in prominent evaginations of the skin of the host, always in the lateroventral region of the body, which may be the result of hyperptrophy of the hypopleural areas. The origin of the cyst is uncertain, but it is most likely part of the cast cuticle of the 1st stage. If this is the true explanation, there is no real encystment such as is found in other species (Clausen 1940/1962).
Mature 1st instar larvae of Hypamblys albopictus are apparently contained within the egg and no direct feeding takes place in this stage (Wardle 1914). Rosenburg (1934) found young larvae of Trichomma enecator Rossi (presumably 2nd instar) in hibernating codling moth larvae. Each one was enveloped in a translucent cyst, or trophamnion. The envelope was closely attached to portions of the fat body of the host and to the tracheae. This attachment was apparently brought about by mere contact: as the cyst enlarges with the growth of the larva it comes in contact with additional tracheae and other portions of the fat body, and a continually increasing attachment is thereby established. The trophamnion persisting as a partial or complete envelope about the 1st instar larva after hatching is not of frequent occurrence as in the Braconidae, however. The infrequent occurrence is correlated with a reduction in egg membrane function, as reflected in a relatively slight enlargement of the embryo during the incubation period.
In superparasitization of the host by an internal parasitoid that is solitary in habit, the surplus individuals are usually eliminated in the first stage, and frequently immediately after hatching. In some species it has been found that this is the result of combat between the larvae, in which the oldest and strongest is probably the victor. When several instars are present in the one host, the youngest is usually victorious because of its better fighting equipment and greater mobility. In Eulimneria crassifemur Thoms. a few larvae are killed by combat but the majority are thought to die through the effect of a cytolitic enzyme given off into the blood stream of the host by the larva that hatches first (Thompson & Parker 1930). Some of the younger individuals die before complete issuance from the egg is accomplished. The mandibulate 2nd instar larva of Collyria calcitrator is much better equipped for combat than are other instars, and thus this, rather than the 1st instar, is responsible for the death of surplus parasitoids (Salt 1931).
Among solitary external parasitoids, the excess individuals are most often destroyed by the first larva that hatches, and this is accomplished not only by combat between those of the same stage of development but frequently by attack upon the remaining unhatched eggs. Among species developing externally on a host contained in a cell, it is the general habit of the 1st instar larva to move about freely over the body and to change the point of feeding frequently. Extreme activity by the 1st instar larvae is particularly evident in the Cryptinae, and it was observed that they frequently leave the host cocoon and wander away if an aperture can be located. This activity is greatly reduced after the first molt, and only a single feeding puncture may be made thereafter. In the various groups in which the larva maintains a fixed connection with the eggshell and thus is restricted to a circumscribed area on the host body, the point of feeding is changed at least once with each molt. This is made necessary by growth of the larva, because of which the head becomes increasingly distant from the point of attachment of the posterior end of the body.
External parasitoid larvae do most of their feeding in the last larval stage, in which suctorial action is replaced by direct feeding upon the body tissues. But in Megarhyssa curvipes Grav. no feeding seems to take place in this stage. The endoparasitic forms that pupate outside the host body complete their larval feeding before emergence, though it is believed that the larva of Thersilochus conotracheli emerges from the host larva and continues its feeding externally, during which time it completely drains the fluid contents from the body. But this habit is much less common than in the Braconidae.
Sometimes a species that is normally an external parasitoid of larval hosts will develop as an internal parasitoid of the pupa of the same species. Husain & Mathur (1924) reported that Melcha nursei Cam. attacks either the mature larva or the pupa of Earias in the cocoon and deposits its eggs externally and that larval development then takes place either externally or internally.
A distinct larval diapause has been found in Exeristes roborator F. by Baker & Jones (1934). Various factors influence the tendency to enter this conditions, though heredity apparently is not involved (Clausen 1940/1962). Almost any change in external conditions adverse to normal development causes some larvae to pass into diapause. Thus a considerable percentage of larvae are in diapause during the winter months. This has no relation to the number of generations intervening since the last diapause. Even when subjected to favorable temperature and humidity, the larvae will persist in that condition for several months. Higher temperatures merely increase the mortality, but the diapause may be broken by exposing the larvae to low temperatures (0.5-1.7°C) for ca. 70 days, followed by a further period under normal developmental conditions. In the second brood of Spilocryptus extrematis, ca. 1/2 the larvae progress immediately to the adult stage, and the remainder go into diapause and become adults the following summer. Occasional individuals persist in the larval stage until the second season following.
In the above instances, the species are in the mature larval stage when they go into diapause, and this is undoubtedly the most common. However, even the 1st instar larvae may undergo a protracted period of quiescence; the observations of Morris on Exenterus abruptorius in central Europe are interesting in that he found that ca. 15% of larvae of this species proceed immediately with their development to maturity feeding being completed in 2-3 weeks, while the remainder persist at 1st instar larvae in the sawfly cocoons for ca. 2 months. This quiescent period occurs during midsummer, but activity begins in sufficient time for the completion of larval development by the end of September. The factors responsible for this diapause are not clearly understood, for they appear to have no relation to climatic conditions (Clausen 1940/1962).
Many endoparasitic species pass a variable and often protracted period as 1st instar larvae within the host body. However, this is not a diapause, inasmuch as it represents merely a cessation of development for a period which is determined by the cycle of the host. In this and other families and orders, the parasitic species often delay larval development until a certain stage of the host, most frequently the prepupal, is attained, at which time the body contents are presumably most suitable for the nutritional demands of the parasitoid (Clausen 1940/1962). Larvae of species of Ichneumoninae that develop in the cells of bees have a specialized feeding habit; they are first predaceous on the early stages of the host and then complete their development on the food that was provided for the latter. The young larva of Grotea anguina sucks out the contents of the egg of Ceratina dupla or destroys the newly hatched larva before beginning to consume the beebread. In the case of Macrogrotea gayi Brethes and Echtropsis porteri Brethes, some feeding may take place on the stored food immediately after hatching, but the host egg or larva is very soon destroyed (Janvier, 1933). Both these species may likewise devour the occupants and food contents of several cells before reaching maturity.
Host larvae that are attacked by internal parasitoids and that continue feeding during a considerable portion of the developmental period of the latter react in several ways to the presence of the parasitoid within the body. Often such individuals will be of smaller size than healthy larvae of the same age, and toward the end of the period they show an appreciable color difference. Another effect of parasitism is in prolonging the active larval period of the host. The healthy larvae of the larch casebearer, Coleophora laricella Hbn., usually spin their cocoons in May while those which are parasitized by Angitia nana Grav. persist in the active stage beyond this time before death occurs. Candura (1928) found that larvae of the Mediterranean flour moth parasitized by Nemeritis canescens Grav. acquire a solitary habit and produce an abnormal amount of silk in web formation.
Pupation habits of Ichneumonidae show very little uniformity. Species that reach larval maturity in or on host larvae in a cocoon, soil cell, tunnel, etc. may spin a cocoon or may pupate without it. Megarhyssa and Xylonomus, that parasitize wood-boring larvae and are thus well protected, spin tough cocoons in the tunnels, while Collyria calcitrator and Scambus detrita Holmg., which attack Cephus larvae in grain stems, do not form cocoons. When larval maturity is attained internally in lepidopterous pupae, the parasitoids pupate in situ, with the body lying in the thoracic region, oriented in the same way as the host, and a light cocoon may be spun. Usually a plug of silk partitions off the greater portion of the abdominal region, which contains a large quantity of waste material. In dipterous puparia no cocoon is spun, and the pupa lies with its head at the anterior end. Voukassovitch ( ) found that ichneumonid larvae which kill the mature host larva in its cocoon consistently orient themselves for pupation so that the head lies at the end opposite the host remains.
Species such as Ephialtes examinator F. may reach larval maturity in either the host larva or pupa. If in the former the parasitoid larva leaves the body before pupation, while in the pupa it transforms in situ as previously noted.
Some gregarious Ichneumoninae reach larval maturity after the host has spun its cocoon and spin their own cocoons longitudinally within that of the host. These may be so numerous as to pack the interior of the cocoon and, in cross section, they are closely pressed together and give a distinctly honeycombed appearance (Clausen 1940/1962). In ichneumonids that are internal parasitoids of free-living larvae and which complete their development before the host spins its cocoon or forms a pupation cell, the cocoon is frequently spun within the host skin, with the head of the pupa directed toward the anterior end. The mature larva of Anilastus ebeninus Grav. (Faure 1926) makes an incision in the venter of the body of the Ascia larva, secretes a quantity of mucilaginous material which binds it to the leaf, and then spins the cocoon within the empty skin. Hyposoter pilosulus Prov. lines the skin of Hyphantria with silk and pupates within it, and Ophion chilensis Spin. and Nemeritis canescens have a similar habit. The larvae of Hyposoter disparis Vier. and Amorphota orgyiae How., emerge from the host larvae and form their cocoons on the nearby foliage.
There is much diversity in form in the cocoons of Ichneumonidae, and some bear distinctive color markings. Those of Polysphincta are usually found suspended in the webs of the host spiders, and they may range from an exceedingly light network of silk, through which the pupa can be clearly seen, to a very compact walled, fusiform cocoon. Some of the latter bear pronounced longitudinal ribs, and in P. pallipes Holmg. the cocoon is square in cross section. Lichtenstein & Rabaud (1922) found some species of the genus, as P. percontatoria Mull., leave an opening at the posterior end of the cocoon, through which the prepupa ejects the string of meconial pellets. The cocoons of this genus are normally suspended in a vertical position in the host web, with the anterior end of the pupa downward.
Some multibrooded species exhibit an unusual adaptation to external conditions in the production of winter cocoons that are quite different in form and color from those produced in the summer generation. Howard (1897) first noted this in the case of Scambus coelebs. In Eulimneria crassifemur, the summer cocoons are thin and whitish and have a distinctly paler ring about the middle, whereas the winter cocoons are oblong-oval in form, of solid texture, and range in color from light gray to almost black (Thompson & Parker 1930). Some lighter colored specimens of the latter exhibit a faint whitish ring about the middle, but this is entirely lacking in the darker cocoons. The summer cocoons have been found only in northern Italy, the southern limit of distribution of the species, and in that section both forms are produced by the summer generation and the adults emerge from both before winter. The occurrence of two types of cocoon has also been noted in the case of Aenoplex carpocapsae (Clausen 1940/1962).
Sphecophaga burra Cress, a parasitoid in the nests of Vespa shows striking cocoon dimorphism (Cushman ; Schmieder 1939). The cocoons designated as typical are thick-walled, tough and brown in color and are firmly attached to the bottom wall of the host cell, while the second form is of a delicate and fluffy texture and is loosely attached to the cell wall at any point. The brown cocoons were twice as numerous as the white ones; and in many cases the colony, consisting of 1-4, had only this form. A smaller number of cells, representing 1/4th the total of those examined, contained cocoons of both forms, indicating that they are from the same parent and from eggs deposited at the same time. Larvae contained in typical cocoons invariably go into diapause, and the adults do not emerge until the following spring, while those in the white cocoons progress to the adult stage and emerge without delay (Clausen 1940/1962).
Clausen (1940/1962) mentioned "jumping cocoons" which are known in several species of Bathyplectes and Eulimneria. Those of B. corvina Thoms. exhibit this peculiarity, whereas it does not occur in B. curculionis, a parasitoid of the same host and of similar habits. The cocoon of B. corvina has been found to jump as much as 2.54 cm from a solid substratum, and this action seems to be accomplished by a sudden straightening of the body of the larva within it, resulting in the ends of the body striking the cocoon wall with considerable force.
There is only a single generation for many species, the cycle usually being correlated with that of the host, and the greater part of the year is passed as inactive larvae. However, Diplazon laetatorius has up to 10 generations per year, and Nemeritis canescens has eight. Faure found that the cycle of Anilastus ebeninus may be completed in 18 days, which is much shorter than for its hosts Ascia spp. This difference in the cycle of parasitoid and host is considered a defect in adaptation, although it should be a decided advantage if the broods of the host are overlapping. In other multibrooded species, the cycle of the summer generations ranges in length from 11-14 days in Tromatobia rufopectus Cress. to almost two months in many others. The actual feeding period of the larva of many ectoparasitic species covers only 3-6 days, although in Tryphoninae, particularly Paniscus, it may be much longer and covers 14-17 days in P. cephalotes Holmg. The egg stage may be much more prolonged in those species of the subfamily in which uterine incubation does not occur, and the actual duration is governed primarily by the age of the host individual attacked. In Pimpla instigator there is an unusual difference in the life cycles of the two sexes, the males requiring only 16-17 days as compared with 24-28 days for females.
Some multibrooded species are known to have long and short cycle phases, with a portion of each brood going into diapause for a considerable period, often until the following season, while the remainder complete their cycle quickly. McClure (1933) in rearing a male brood of Aenoplex carpocapsae, found a wide range in the time required for development from egg to adult. The majority were of the short-cycle phase, completing development in ca. 19 days, as compared with 71 days for the long-cycle parasitoids. This difference in time is taken up almost entirely in the larval resting stage. Janvier found that emergence of adults from a group of cocoons of Cryptus horsti formed at the same time extended over a period of several months.
Species of Polysphincta have usually two generations each year, and there is a great variation among individuals in the duration of the larval stage. The larvae of of this genus to undergo prolonged periods of inactivity. When the spider host is without food, the parasitoid larva apparently ceases feeding and yet is able to live for several months. Development is resumed as soon as host feeding resumes.
Hibernation takes place most often in the mature larval stage in the cocoon. This is true in particular for Cryptinae, Tryphoninae and Ichneumoninae, of which a considerable number of species have been studied. In the latter subfamily, Collyria calcitrator is an exception; it passes the winter as a 3rd or 4th instar larva in the living sawfly host. Glypta rufiscutellaris, a parasitoid of the larvae of the oriental fruit moth and others, passes the winter as a mature larva in the cocoon and has three generations per year, corresponding to the host cycle. G. haesitator Grav, which attacks Cydia nigricana Steph., a single-brooded host, has only on generation and passes the winter as a 2nd instar larva within the host. Cremastus flavoorbitalis, Heteropelma calcator, and Therion morio hibernate in the first larval stage within the host, and in several species the larva is enveloped in a cyst during this entire period. Some species of Polysphincta appear to pass the winter in the early larval stages upon the body of the host. Nielsen stated that young Theridium lunulatum coming out of hibernation in the early spring bear the small parasitoid larvae upon the body (Clausen 1940/1962). Phaeogenes nigridens is said to persist only as adult females; and according to H. D. Smith, the majority of species of the family that hibernate as adults belong to the Joppinae. A number of Ophioninae have the same habit, and Hyposoter disparis and Thersilochus conotracheli attain the adult form during the autumn but remain within the cocoon until spring. Both Seyrig (1924) and Townes (1938) mentioned the finding of adult females of many Ichneumoninae during the winter, some species being consistently under bark, while others are in empty tunnels in decaying wood, in clumps of dry grass, or in other sheltered places.
There is usually a preponderance of females in bisexual species, with the greatest excess recorded in Pimpla pomorum Ratz. which has ca. 75% &&. However, in some species males predominate under field conditions. Chewyreuv (1913) and others noted that the sex of the parasitoid progeny was correlated with the size of the hosts in which development takes place. The males develop mostly in small hosts and females in larger ones. This was most evident among species attacking pupae and explains the differing sex ratios secured for a species on several hosts and at different seasons. Working with Pimpla spp., Chewyreuv found that large host pupae from the field consistently yielded a high percentage of females, while smaller hosts produced mostly males. Laboratory tests supported these findings, for all large pupae produced females, and 80% of the small ones yielded males. This disparity in sex ratio is attributed to selective oviposition by the parasitoid female. When oviposition takes place on or in the host larva at almost any stage of its development, and the host is killed only after the cocoon is formed, as in those attacked by Exenterus and Campoplex, the mechanics of this selective process are more difficult to determine than when attack is on the pupa, which is already at its full size (Clausen 1940/1962).
Some species reproduce unisexually. Clausen (1940/1962) notes that the production of 26 consecutive generations of Hemiteles areator Panz. did not yield a single male, although Muesebeck & Dhoanian (1927) found that unmated females produced only males. They recorded the production of 12 generations of females of H. tenellus Say in three years and stated that the male is unknown. Nemeritis canescens, Sphecophaga burra, and Polysphincta pallipes reproduce in the same fashion, and the large scale rearings of the first named species by various workers have shown only an occasional male (Clausen 1940/1962).
Ichneumonidae show a variable reproductive capacity. Phaeogenes nigridens deposits a total of ca. 50 eggs, and Clausen (1940) thought that many Ichneumoninae probably do not much exceed this number. However, Exeristes roborator was found to deposit up to 40 eggs per day and a maximum of 679 (Baker & Jones 1934). In Ophioninae, the number is often considerably higher. The maximum recorded is for Hyposoterdisparis, of which a series of females produced an average of 561 eggs and one individual deposited 1,228 (Muesebeck & Parker 1933). The ovaries of a number of species showed the presence of a total of 200-400 eggs in various stages of development. Meyer (1926) stated that Angitia fenestralis Holmg. was able to produce a total of at least 540 eggs. Among the Tryphoninae the capacity is usually comparatively low, although females of Hypamblys albopictus are thought to contain up to 448 eggs. In this subfamily there is a marked disparity in the reproductive capacities of the ectoparasitic and the endoparasitic species.
Generally there are 2-8 mature eggs in each ovariole, which probably represents the potential daily capacity. Therefore the number of ovarioles determines the rate of egg deposition. Glypta rufiscutellaris and H. albopictus have the largest number recorded, which is ca. 56, while most Ichneumoninae, Cryptinae and the ectoparasitic Triphoninae have a smaller number (8-16) (Clausen 1940/1962).
For detailed descrptions of the immature stages of Ichneumonidae, please see Clausen (1940/1962).
Aerts, W. 1957. Die Schlupfwespen - (Ichneumoniden-) Fauna des Rheinlandes. Decheniana 109: 137-212.
Aubert, J. F. 1957. Révision partielle des Ichneumonides Gelis Thnbg. (= Pezomachus Grav.) et Perosis Först. de la collection A. Förster et notes concernant les travaux qui s'y rapportent. Mitt. münch. ent. Ges. 47: 222-64.
Benoit. P. L. G. 1956. Ichneumonidae nouveaux ou interessants de l'Afrique du Sud. Ann. Soc. Afr. Mus. 43: 123-35.
Benoit, P. L. G. 1956. Nouvelles espèces africaines du genre Foenatopus Smith (Hym., Stephanidae). Bull. Ann. Soc. R. Ent. Belg. 92: 205-12.
Bou…ek, Z. 1955. On a new genus of Braconidae (Hymenoptera) with remarks on the wing nomenclature. Acta Ent. Mus. Natl. Pragae 30: 441-6.
„apek, M. 1956. A new genus and species of Braconidae from Slovakia. Folia Zool. 5(19): 285-7.
„apek, M. & H. Zwölfer. 1957. apanteles murinanae nov. sp. (Braconidae, Hym.) ein neuer Parasit des Tannentriebwicklers. Mitt. schweiz. ent. Ges. 30: 119-26.
Chao, H. F. 1957. REcords of Ichneumon-flies from Fukien Province, with description of anew species (Hym., Ichneumonidae). Acta Ent. Sinica 7: 105-112.
Clausen, C. P. 1940. Entomophagous Insects. McGraw-Hill, NY. 688 p.
Constantineanu, M. J. 1956. Nouvelles espèces d'Ichneumonides pour la faune de la région de Iassy. Acad. R.P.R., Etud. Rech. Sci. 6: 35-47.
Constantineanu, M. J. 1956. Contributions à la faune des Ichneumonides de la République populaire roumaine. La sous-famille des Ichneumoninae dans la région de Succava. Acad. R.P.R., Etud. Rech. Sci. 6: 49-71.
Constantineanu, M. J., I. Andriescu & V. Ciochia. 1956. Contributions à la connaissance de la faune des Ichneumonides de la République populaire roumaine. La sous-famille des Ichneumoninae Förster dans le nord-ouest de l'Olténie. Ann. Sci. Univ. Al. I. Cuza, Iassy 2: 85-111.
Constantineanu, M. J., I. Suciu, I. Andriescu, V. Ciochia & C. Pisica. 1957. Contributions à la connaissance des Ichneumonides en R.P.R. Sous-famille Ichneumoninae Förster, arrondissement de Husi, Région de Iassy. Ann. Sci. Univ. Al. I. Cuza, Iassy 3: 234-63.
Cushman, R. A. 1926. Proc. Wash. Ent. Soc. 28: 29-51.
Fernando, E. F. W. 1956. A new species of Spilophion (Ichneumonidae, Hymenoptera) from Ceylon. Ann. Mag. Nat. Hist. 9: 666-8.
Fernando, E. F. W. 1956. A new species of Goryphus (Ichneumonoidea, Hymenoptera) from Ceylon. Ann. Mag. Nat. Hist. 9: 878-80.
Fischer, M. 1957. Neue Palaearktische Meteorus- Arten (Hym., Braconidae). Ann. naturh. Mus. Wien 61: 104-9.
Fischer, M. 1957. Die Opiinen-Typen der Sammlung Förster aus dem Zoologischen Museum in Berlin (Hym., Braconidae). Deutsch. Ent. Z. 4: 47-53.
Fischer, M. 1957. Die europäischen Arten der Gattung Opius Wesm. (Hym., Braconidae). Deutsch. Ent. Z. 4: 332-58.
Fischer, M. 1957. Beiträge zur Kenntnis der palaearktischen Braconiden (Hymenoptera). Mitt. München. Ent. Ges. 47: 1-21.
Fischer, M. 1957. Neue Opius- Arten aus Schweden (Hym., Braconidae). Opusc. Ent. 22: 211-25.
Fullaway, D. T. 1957. A new reared Opius from Africa (Hymenoptera, Braconidae). proc. Ent. Soc. Wash. 59: 98-9.
Gupta, V. K. 1957. Pristomerus testaceacollis Cameron-- A nomen nudum (Insecta: Hymenoptera, Ichneumonidae). Cur. Sci. 26: 152-3.
Heinrich, G. H. 1956. Holarctic elements among the Ichneumoninae of Canada. Canad. Ent. 88: 647-52.
Heinrich, G. H. 1956. Ichneumon lariae Curtis, a critical study on this arctic species and its closely related forms. Canad. Ent. 88: 686-91.
Heinrich, G. H. 1957. A new species of the tribe Trogini (Hymenoptera, Ichneumonidae). Canad. Ent. 89: 334.
Hellén, W. 1957. Zur Kenntnis der Braconidae: Cyclostomi Finnlands. Notulae Ent. 37: 33-52.
Heqvist, K. J. 1957. Studien über Braconiden. III. Paracedria n. gen., eine neue Gattung der Horminae aus Schweden. Ent. Ts. 77: 219-20.
Heqvist, K. J. 1957. Studien über Braconidien. IV. Eigenartige Flügelbnormität bei Helcon annulicornis Nees. Ent. Ts. 78: 28.
Hinz, R. 1975. Zur Systematik und Oekologie der Ichneumoniden. I. (Hym.). Deutsch. ent. Z. 4: 86-90.
Jourdheuil, P. 1957. Description d'un ichneumonide (Mesochorini) parasite secondaire de diverses espèces de Phyllotreta (Hym., Ichneumonidae). Bull. Soc. ent. France 62: 41-5.
Kerrich, G. J. 1957. Systematic note on Rhorus substitutor (Thunberg) (Hym., Ichneumonidae). Ent. Ts. 78: 272-3.
Lima, A. da Costa. 1956. Tortricid from seeds of imbuia (Phoebe porosa) and its parasite (Hymenoptera, Braconidae). REv. Bras. Ent. 5: 219-24.
Mason, W. R. M. 1957. A new genus and species of Microgasterinae (Hymenoptera, Braconidae). Canad. Ent. 89: 355-57.
Muesebeck, C. F. W. 1956. Some braconid parasites of the pink bollworm Pectinophora gossypiella (Saunders). Boll. Lab. Zool. Gen. Agr. Portici 33: 57-68.
Muesebeck, C. F. W. 1957. New world Apanteles parasitic on Diatraea (Hymenoptera: Braconidae). Ent. News 68: 19-25.
Nixon, G. E. J. 1956. Two new braconid parasites of Loxostege frustalis Zell. in South Africa. J. Ent. Soc. South Afr. 19: 128-31.
Noskiewicz, J. 1957. Remarques sur les espèces du groupe de Megarhyssa superba Schrk. en Silésie (Hymenoptera, Ichneumonidae). Polsk. Pismo Ent. 26: 321-31.
Orfila, R. N. 1956. Los Stephanidae (Hym.) artentinos. REv. Soc. Ent. Argent., 19: 5-8.
Parrot, A. W. 1957. Notes on the host relation of some Australian Ichneumonidae, with a description of a new species. Mem. Natl. Mus. Victoria 21: 79-82.
Perkins, J. F. 1957. Notes on some Eurasian Itoplectis with descriptions of new species (Hym., Ichneumonidae). Mitt. schweiz. ent. Ges. 30: 323-6.
Porter, C. C. 1975. A new subspecies of Megarhyssa atrata (Fabricius) (Hymenoptera: Ichneumonidae). Ent. News 68: 206.
Rao, B. R. S. 1955. A new species of Chelonus on Heliothis armigera (Fabricius). Indian J. Ent. 17: 63-4.
Richards, O. W. 1957. A note on the genus Mirax Hal. (Hym., Braconidae, Microgasterinae). Entomologist 90: 120-2.
Santis, L. de. 1956. Anotaciones sobre Ichneumonoideos argentinos con descripción de una especie nueva (Hymenoptera). Notas Mus. La Plata (Zool.) 18: 303-12.
Shenefelt, R. D. & C. F. W. Muesebeck. 1975. Ashmead's Meteoridea (Hymenoptera, Braconidae). proc. Ent. Soc. Wash. 59: 129-34.
Short, J. R. T. 1957. On the final instar larva of Stilbops (Aphanoroptrum) abdominale (Grav.) (Hymenoptera: Ichneumonidae). proc. R. ent. Soc. Lond (B) 26: 175-6.
Starý, P. 1957. On the braconid genus Zele Curtis of Czechoslovakia (Hym., Braconidae) (Notes on the Braconidae of Czechoslovakia, III.). Acta Soc. Ent. „echosl. 54: 66-72.
Starý, P. 1957. Notes on the Braconidae (Hym.) of Czechoslovakia IV. (Part I). Acta Soc. Ent „echosl. 54: 277-92.
Starý, P. 1957. Notes on the synonymy of Heterogamus excavatus Telenga, 1941 and Heterogamus (Jirunia) farmakena Mala…, 1941 (Hym., Braconidae). Acta Soc. Ent. „echosl. 54: 293-5.
Stelfox, A. W. 1957. Further new species of Dacnusini (Hym., Braconidae) from Ireland and notes on several other species. Ent. Mon. Mag. 93: 111-20.
Stelfox, A. W. 1975. A new name for Opius nitidus Stelfox, 1948 (Hym., Braconidae). Ent. Mon. Mag. 93: 212.
Tobias, V. I. 1957. New subgenera and species of the genera Bracon F. and Habrobracon Ashm. (Hymenoptera, Braconidae) from the steppe and desert regions of the USSR. REv. Ent. URSS 36: 476-500.
Tobias, V. I. 1957. On morphology, taxonomy and phylogeny of the supertribus Braconina Tel. (Hymenoptera, Braconidae). Zool. Zhur. 36: 1338-54.
Townes, H. 1944. Mem. Amer. Ent. Soc. 11: 1-925.
Townes, H. 1956. Biological characteristics of taxonomic groupings in the Ichneumonidae. Bull. Ent. Soc. Amer. 2: 18.
Townes, H. 1957. A revision of the genera of Poemeniini and Xoridinni (Hymenoptera, Ichneumonidae). Proc. Ent. Soc. Wash. 59: 15-23.
Townes, H. 1957. A review of the generic names proposed for Old World ichneumonids, the types of whose genotypes are in Japan, Formosa or North America 9Hymenoptera, Ichneumonidae). Proc. Ent. Soc. Wash. 59: 100-20.
Townes, H. 1969-72. Five volumes on genera of Ichneumonidae of the world. Mem. Amer. Ent. Inst.
Uchida, T. 1956. Ein neuer Schmarotzer der Larvae von Artopoetes pryeri. Ins. Matsum. 20: 48-9.
Uchida, T. 1956. Neue oder bisher unbekannte Ichneumoniden aus Japan und seinen Umgegenden (1). Ins. Matsum. 20: 57-76.
Uchida, T. 1957. Ein neuer Schmarotzer der Kartoffelmotte in Japan (Hymenoptera, Ichneumonidae). Mushi 30: 29-30.
Uchida, T. 1957. Zwei neue Arten und eine neue Gattung der Ichneumoniden. Ins. Matsum. 21: 41-44.
Uchida, T. 1957. Drei aus den Schmetterlingslarven gezüchteten Ichneumonidenarten. Ins. Matsum. 21: 59-61.
Uchida, T. 1957. Beiträge zur Kenntnis der Diplazoninen-Fauna Japans und seiner Umgegenden 9Hymenoptera, Ichneumonidae). J. Hokkaido Univ. Fac. Agr. 50: 225-65.
Uchida, T. & S. Momoi. 1957. Descriptions of three new species of the tribe Ephialtini from Japan (Hymenoptera, Ichneumonidae). Ins. Matsum. 21: 6-11.
Ueda, S. 1956. Description of the male of Epirhyssa nitobei Uchida (Hymenoptera: Ichneumonide). Kontyu 24: 212-14.
Victorov, G. A. 1957. Species of the genus Enicospilus Stephens (Hymenoptera, Ichneumonidae) in URSS. Rev. Ent. URSS 36: 179-210.
Walkley, L. M. 1956. A tribal revision of the Brachycyrtine wasps of the world (Cryptinae, Ichneumonide). proc. U. S. Natl. Mus. 106: 315-29.
Watanabe, C. 1957. A new species of Aspilota Förster parasitic on the chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera, Braconidae). Mushi 30: 35-6.
Watanabe, C. 1957. Notes on Ashmead's Japanese Braconidae (Hymenoptera). Ins. Matsum. 21: 1-5.
Watanabe, C. 1957. Notes on Japanese and Formosan species of Stantonia Ashmead (Hymenoptera, Braconidae). Ins. Matsum. 21: 45.
Watanabe, C. 1957. A revision of Rogas pallidinervis Cameron (Hymenoptera, Braconidae). Ins. Matsum. 21: 46-7.