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HYMENOPTERA, Ichneumonidae (Leach 1817) - (Ichneumonoidea) -- <Overview> <Adults-1> & <Adults-2> & <Adults-3>; & <Juveniles> Please CLICK on Links to navigate; Depress Ctrl/F to search for Subjects 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ovipositor issues from the tip of the abdomen and is withdrawn into the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). Host Preferences
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). Biology
& Behavior
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. Life Cycle
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. Parthenogenesis & Sex Ratio
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). Reproductive Capacity
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). References: Please refer to <biology.ref.htm>, [Additional references may be found at: MELVYL
Library] Aerts, W.
1957. Die Schlupfwespen - (Ichneumoniden-)
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