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CHARACTERISTICS OF THE HYMENOPTERA
[Also See: ID Keys: Great Britain, Palearctic
The order has two suborders, the Symphyta and the Apocrita: The Symphyta includes species with a very
generalized form, both as adults and as larvae. None of them show the
specialized habits that typify most of the other Apocrita, and they are primarily phytophagous. The first
abdominal segment is not completely fused to the metathorax nor does the
constricted waist that is characteristic of the remaining Hymenoptera
accompany the fusion. The ovipositor
is used as an apparatus for piercing plant tissues. The trochanter has two
joints. Larvae are eruciform and in addition to thoracic legs some the
abdominal segments may have prolegs that are without distal crotchets or
spines (Please see Glossary for terminology).
This group includes the
wood-wasps, the ovipositors of which are used as drills for perforating
timber in which the eggs are laid. The 6-legged, strong larva bores through
the wood (in the case of Sirex gigas, this
stage lasts for two years). Pupation
occurs near the surface of the affected timber, from which the adult bites
its way out. The sawflies with saw-like ovipositors, are most important as
agricultural pests, and are different from the wood-wasps by having softer
bodies, their smaller size, and by the presence of two apical spurs on the
The Apocrita includes all the other Hymenoptera. The
second abdominal segment is constricted to form a narrow waist or petiole,
the first segment being firmly joined with the thorax. Larvae are apodous when full-grown. Ichneumon flies have slender curved
antennae, and there is a stigma on the wing. The ovipositor is generally long
and projects forward from the tip of the abdomen. The larvae of Lepidoptera
and of sawflies are their usual hosts.
Cyanamid "flies" also have slender
antennae, but there is no stigma on the wing and there is a reduced
venation. Many of these form galls on
plants, while others are
parasitic on fly larvae.
Chalcid wasps also have the
wing venation reduced with no closed cells. The antennae are geniculate or
elbowed. Though most of these small wasps are parasites, e.g. of
lepidopterous and dipterous larvae, and of homopterous nymphs, a few feed on
Ichneumonids, chalcids and cynipids
have the ovipositor coming from beneath the abdomen well in front of its tip,
and these insects differ in this feature from the Proctotrypidae where the ovipositor is terminal. Dipterous larvae are often parasitized by
these insects, as are also the eggs of Orthoptera and Hemiptera. Many
hyperparasites occur in this family.
The ants (Formicoidea)
are social, polymorphic insects in which two segments form the
abdominal petiole. Moreover, this petiole always has one or two nodes. The females have a well-developed stinging
apparatus which is a modified ovipositor. Polymorphism reaches its highest
degree of complexity in this group, as many as 30 different castes having
been found. Some of these are
pathological phases due to infection by parasites, e.g. nematode worms, or
other Hymenoptera. In colonies that have winged forms of both sexes, mating
takes place during a nuptial flight in which several colonies are involved at
the same time. This permits interbreeding between individuals from different
colonies. The females then cast off their wings and begin colonies in the
ground.. The workers are sterile females, whose ability to lay eggs in
certain circumstances may be restored. For example, when a colony loses a
queen several workers may, under the stimulus of diet, take her place.
In addition to the environmental
complexity, which a social existence involves, association with other
organisms complicates the lives of ants. Some have adopted an agricultural
habit, living on fungi that they cultivate. Others gather seeds from which
they destroy the radicle to prevent germination. Special chambers or
granaries in the nest are constructed for their storage. A pastoral habit is
found in others, a symbiotic relation being set up with such insects (e.g.
aphids) because they exude fluids that are coveted to the ants. There are numerous other associations of a
different nature that range from the symbiotic to the parasitic. Finally
there are the slave-makers: Formica
sanguinea, e.g.,, captures from the colonies of F. fusca pupae which on emergence serve
as slaves in the colony which has adopted them (Borradaile & Potts, 1958).
The wasps of the superfamily Vespoidea are both social and solitary
in habit. In these, the abdominal petiole is smooth and, species with a
worker caste are always winged. The prothoracic tergum extends back towards
the wing base. Wasps are primarily
carnivorous. Rarely are they
phytophagous as in some solitary masarine wasps that feed their larvae on pollen
and honey. Among solitary species may be mentioned Odynerus which deposits caterpillars in its nest when its
larvae are developing. Pompilid wasps are entirely predatory on spiders. Other groups have adopted the 'cuckoo'
habit, laying their eggs in the nests prepared and provisioned by other
species. Social wasps, e.g. Vespa, live in nests usually constructed
of paper obtained in the form of wood pulp. The larvae, living in cells on
horizontal combs, are fed on insect food gathered by the workers. In early
summer the social wasps feed on such insects as plant lice, etc., but later
in the season they search for sweet fruits, which make them annoying, both in
the garden and in structures. In autumn the colony dies, fertilized females
being the only survivors. The inability to store animal food on which the
larvae rely explains the disappearance of colonies in autumn. Only in
tropical regions where food is plentiful throughout the year do wasp colonies
Closely resembling the Vespoidea are the wasps belonging to the
superfamily Sphecoidea, the
distinctive character of which is the possession of a prothoracic tergurn
that does not extend back as far as the wing bases. These are all solitary
predaceous forms, which sting their prey and paralyze them before placing
them in the larval cells, which have been previously prepared.
The superfamily Apoidea includes social and solitary
bees. Bees are recognizable by their dilated hind tarsi and the plumose hairs
of the head and body that acquire pollen. There are also inner metatarsal
spines of the posterior legs that comb the hairs free of pollen. The pollen is then transferred to the
outer upturned spines (pollen basket) of the hind tibia of the opposite side.
These legs are further adapted with spines for the manipulation of wax plates
when being removed from the abdomen. The median glossa is also typical and in
certain solitary forms, e.g. Anthophora and
all the social bees, e.g. Apis and
Bombus, is greatly elongated
along with the parts other than the mandibles for gathering nectar from deep-seated
flower nectaries. Larvae are fed exclusively on pollen, nectar and salivary
fluids. Megachile, the
leaf-cutter, is a solitary bee that makes cells of neatly cut leaf fragments.
Each cell containing an egg is stored with honey and pollen. Such cells are
commonly made in the walls of houses, the mortar being removed for this
purpose. Andrena constructs
burrows in the ground and, though solitary, is usually found in groups of
individuals occupying a common terrain that may include a 'village' of several
hundred nests. Nomada has
adopted the 'cuckoo' habit (Borradaile & Potts, 1958).
Bombus spp. are similar to the Vespa spp. in that only impregnated females survive the
winter. The colony of the honeybee Apis
mellifera is more permanent, only the males dying off in the
autumn to leave the rest of the colony to hibernate. The nest is constructed
of wax, an exudation from abdominal glands of the worker (sterile female),
and a material of vegetable origin fastens parts of the
nest together thereby making the whole weatherproof.
The workers of Apis are graded according to age into nurses, who see to the welfare of the
larvae by incorporating salivary juices with their food, ventilators who, by wing-fanning, set up
currents in the nest or hive to reduce the temperature and to evaporate the
honey, scavengers or cleaners, and foragers who collect pollen and nectar. The changes from
nursery work to housework and to fieldwork are necessitated by changes in
glandular capacity as age increases. Though the density of the population of
the colony determines to some extent when a queen with a number of workers
will depart from the hive as a swarm, it appears that this event is also
dependent on other factors not as yet clear, one of which is the relative
proportions of the above age-groups among the worker caste. The sexes are
determined by a cytological mechanism. Thus, in bees, wasps and ants, haploid
parthenogenesis results in the production of males. A fertilized (diploid)
female has control over the fertilization of eggs that she lays. If an egg is
fertilized by sperm from the spermatheca a female (diploid) offspring
develops; if not, a male offspring (haploid) develops. Whether a young female
becomes a worker (sterile) or a queen (capable of fertilization) depends on
& Potts, 1958).
The mouthparts of the Hymenoptera are
adapted primarily for biting and often for sucking. There are two pairs of membranous wings joined by hooks on the anterior border of the hind wing joined with
a groove on the posterior border of the forewing. The hind wings are smaller.
The first segment of the abdomen is fused to the thorax, and a
constriction behind this segment usually is present. There is always an
ovipositor that is modified for piercing, sawing, or stinging. Metamorphosis is holometabolous. The larvae are usually without legs and
rarely erusiform with thoracic and abdominal legs. The pupae are exarate
regularly protected in a cocoon.
The Hymenoptera are remarkable for
their great specialization of structure, for their varying degrees of social
organization and for the highly developed condition that parasitism has
mouthparts are complex in some cases but they seem hardly ever to have wholly
lost the various parts recognizable in the generalized Orthoptera body plan.
The high point of their development is in Apis,
the honeybee, and their least modified condition is in sawflies.
There also have developed certain
parts of the head capsule that are common to all but the more generalized
Hymenoptera. Thus the head articulates with the thorax by a narrow neck and
the occipital foramen that is
small and bounded below by a strong hypostomal foramen. The union
of the post genae forms this. Great
mobility is thereby possible of the head; the hypostomal bridge forms a
strong base for the attachment of the maxillo-labial complex. In all
Hymenoptera this complex is formed by the union in a common membrane of the
maxillae and labium that are thus placed in a close working relationship with
each other. The working of maxillae and labium as a functional unit is
further ensured by their basal segments, cardo and stipes, submentum and
prementum, being so arranged as to bend in a common plane. Folding of the mouthparts under the head
when at rest, as well as their forward extension when in use, is facilitated.
In these several features, most of which are present in generalized forms,
there are the foundations on which the structural evolution of the higher
forms is based and without which these might never have developed (Borradaile & Potts, 1958).
Among the sawflies are to be found
the most generalized mouthparts. Wasps, too, are easily referable in these respects
to the primitive omnivorous types with the additional feature of adaptation
to licking of fluids by an extension of the bifid glossa and the setose
maxillary galea. The mandibles here are well suited by their toothed form to
feeding on solid food.
Among the sawflies are to be found the most generalized mouthparts.
Wasps, too, are easily referable in these respects to the primitive
omnivorous types with the additional feature of adaptation to licking of
fluids by an extension of the bifid glossa and the setose maxillary galea.
The mandibles here are well suited by their toothed form to feeding on solid
At the other end of the scale of
specialization there is the elaborate elongated and extensible mouthparts of Apis, the honeybee. The mandibles are large, smooth, spatulate
structures articulated to the gena of the cranium. They are used for
manipulation of wax and pollen within the hive and not for the gathering of
The labium has a short triangular
postmentum, to the front border of which is articulated a long prementum.
From this there projects forwards a long tongue, formed from fused glossae,
and which is setose externally and grooved ventrally. At the base of the
tongue are the short curved paraglossae, holding it in such a way as to
conduct fluid from the ventral glossal groove to the upper surface of the
tongue base and so to the mouth that lies above. Arising also from the distal end of the prementum are the
labial palps consisting of several long segments whose inner surfaces, being
concave, can partly encircle the bee's tongue ventrally for the whole of its
In line with the postmentum
lies the maxillary cardo at each side. Basally each cardo is articulated to a
cephalic apodeme that projects inwards to the head cavity. At its distal end
it articulates both with the stipes and with a V-shaped sclerite, the lorum.
This lies in the membrane that unites the labium with the maxillae and
probably develops as a specialization of it. The locum thus connects the two
maxillae with each other, and into its apex fits the proximal angular border
of the postmentum. The stipes of each maxilla lies at the side of the
prementum and is of about the same length. Distally, on its outer side, lies
the much-reduced maxillary palp, and on its inner side a similarly reduced
lacinea. From between these two there projects the curved, blade-like, long
galea. The two galeae have concave inner surfaces, like the labial palps, and
with these latter complete the encirclement of the tongue dorsally.
Food can be drawn up the
ventral groove of the tongue by capillary action, but it can also pass in
larger quantities into the space surrounding the tongue enclosed by the
galeae and the labial palps, passing within the folds of the paraglossae and
being thereby directed to the mouth, which opens above this point. Such
a feeding mechanism is the climax in an evolutionary process which has
involved in succession the fusion of the glossa lobes, as in the sawflies,
the lengthening of the basal joints of the labium and maxilla as in Colletes, and the elongation of the
glossa, e.g. Apis and Bombus.
The highly complex social organization in the bees,
ants and wasps, in which caste development is of prime importance, is foreshadowed
in the interesting behavior of solitary wasps and bees. The supply of food to
the larva by progressive feeding, instead
of mass provisioning, appears
to help the parent to become acquainted with its offspring, and this
establishment of family life may be regarded as the forerunner of the complex
social state of the higher forms. For instance, in the wasp Odynerus the egg is laid in a cell and
sufficient caterpillars stored to serve as food for the whole of the larval
life Some African species of this genus supply their growing larvae daily
with fresh caterpillars (Borradaile & Potts, 1958).
Another important aspect in the
development of social life has been that of trophallaxis. Among wasps the worker taking food to a grub receives in
turn a drop of saliva from the grub. The workers eagerly look for this, and
it is thought that it is the mutual exchange of food between young and adult
that creates in the adult an interest in the welfare of the colony. That the
exploitation of a particular form of abundant food has contributed to the
development of the social system is obvious. As examples there is pollen and
honey for bees and dung as a basis for the simpler social life of some
beetles. No feature determining cohesion of the bee colony seems to be of
such paramount importance as the ability of the queen to satisfy the craving
for a secretion produced by her (queen substance) which all members of the
colony experience. The absence of a queen is rapidly sensed by the colony and
its communal behavior consequently greatly disturbed. Ants and termites
appear to be similarly dependent on the queen.
The complex environment in
which a social insect lives has produced a form of behavior simulating
intelligence. Bees, for example, can with great effect inform one another of
the presence of a food source. They can further inform each other by scent
and, dance of the position of the food source with considerable precision
provided the sky is not wholly overcast.
The direction of the dance movement refers to the position of the sun
in the sky relative to the hive. Because this position can be determined by
the bees in a sky when the sun is not visible, though in which some blue sky
is present, the ommatidia of the compound eye enable the bee to analyze the
degree of polarization of light emerging from a blue patch. It may be concluded that associated with
the social state's development, there has come about a complexity of behavior
that ultimately depends in turn on the enhanced sensitivity of the members of
A kind of parasitism known as
"parasitoidism" is highly developed in the Hymenoptera, with the
ichneumons, chalcids and proctotrypids being almost entirely parasitic.
Almost all orders of insects are affected by the activities of these groups,
the egg, larval, pupal and adult stages all being parasitized. Insects with parasitic habits are divided
into (1) Koinabionts and (2) Idiobionts (Please see <koiidio.htm> for comparison ).
The Hymenoptera contains some
of the most economically important insects. The sawflies are important as
agricultural pests. Flower-visiting bees are of great value in the
pollination of flowers. Carnivorous wasps devour other insect pests such as
aphids, while to a large extent the parasitic Hymenoptera are useful in
regulating the populations of phytophagous insects as has been proven by
numerous biological control campaigns.
Two main types of larvae are
found in this order, the legged larva of the sawflies and the legless form of
bees, wasps and ants. The sawfly
larva has an outward resemblance to the lepidopterous caterpillar, but is
easily distinguished by its single pair of ocelli and the absence of crotchets
or spines on the abdominal legs. The prolegs of the abdomen occur on
different segments (Borradaile & Potts, 1958).
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Detailed Morphology & Habits
The Hymenoptera ranks second in the
number of insect species next to the Coleoptera. They also contain the greatest number of beneficial insect
species. Two-paired and clear wings
characterize them the front wings being largest. A stigma often occurs on the coastal margin. Venation is very variable, however. Some species are wingless, which is
especially true in the parasitic groups.
Hamuli or hooks are
present on the costal margin of the hind wing, which engage with a ridge on
the posterior portion of the forewing to hold the wings together. This enables the wings to operate together
as a single unit. Three ocelli are usually present.
The mouthparts are usually of the
chewing type, but there many species with a lapping-sucking type. The mandible is used for chewing, cutting,
molding wax, forming cells, etc. The
labium and maxillae are considerably modified in the bees.
The meso- and metathorax are well
developed, but he prothorax is reduced.
The first segment of the abdomen is fused with the thorax and is
called the propodeum. The second abdominal segment is often a petiole and the remaining portion the gaster.
Most narrow-waisted species are beneficial while broad waisted species
are usually harmful (e.g., sawflies).
The ovipositor is used to bore,
pierce or to reach into crevices in order to deposit eggs. It is often associated with poison glands
and ducts. For example, some wasps
sting lepidopterous caterpillars with just enough poison to immobilize them. This then serves as fresh food for the
developing wasp larvae.
The pupae are exarate and may be
either naked or enclosed in a cocoon, but much variation may occur within one
Subdivisions and Classification
There are two suborders: Symphyta (Chalastogastra) are the sawflies
and Apocrita (Clistogastra) are all other groups.
have eruciform larvae and their prolegs are without crochets may
occur on all abdominal segments. The
adults have the abdomen broadly joined with the thorax. The ovipositor is adapted for piercing so
that their eggs may be laid in hard wood.
There are many pestiferous species in this group.
contains the largest number of species of Hymenoptera. Their larvae are grub like without
legs. Some develop as grubs on other
animals and their mother nourishes some.
The adults have a distinct petiole, and in some ant species both the
second and third abdominal segments may form the petiole. A node is usually present.
OF PRIMARY MEDICAL IMPORTANCE
The Hymenoptera as a group are
considered more important to humanity than for the few groups that inflict
injury, and even death, to humans and animals by their poisonous stings. Their attributes as pollinators of food
plants, honey production are well known.
However, probably far outnumbering any other group are the parasitic
Hymenoptera that by their constant interaction with other insect populations
maintain stability in the ecosystem.
There are probably over one million species of the parasitic group.
Stressing their adverse effects as stinging insects, Matheson (1950)
pointed out that they are provided with a sting, which is a modified
ovipositor and which is connected with special poison glands. He noted that all stinging insects belong
to the Hymenoptera, which include the families Apidae (honeybees), Bombidae
(bumblebees), Vesidae (wasps & hornets), Sphecidae (digger wasps),
Mutillidae (velvet ants), Formicidae (stinging ants) and others of lesser
importance for troubling animals and humans.
Avoidance is probably the best tactic
for control of stinging insects. It
is especially important to avoid contact with their nests. Wasps are especially provoked by human
proximity to their nests and will attack in large numbers, causing death in
susceptible individuals. The
unfortunate hybridization in Brazil of Italian and African strains of the
honeybee has produced a very aggressive new strain (the "Killer
Bee") that spread throughout the Americas, and which has as of 2016
resulted in the death of many humans and animals (Legner 1990).
Available to the general public are a number of
pesticides that when applied to adults as direct killing agents or in
poisoned baits are temporarily effective.
It is important to restrict adulticides to nighttime applications when
wasps and killer bees are inactive.
To control ants, such as the Argentine ant, applying poisoned baits
around a dwelling will reduce the numbers entering the house. However, many of the products available
have little or no effect due to insecticide resistance. And the overuse of any product in one area
will reduce its effectiveness as the local population develops resistance.
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Key References: <medvet.ref.htm> <Hexapoda>
Matheson, R. 1950. Medical Entomology. Comstock Publ. Co, Inc. 610 p.
Service, M. 2008.
Medical Entomology For Students.
Cambridge Univ. Press. 289 p
Legner, E. F. 1995. Biological control of Diptera of medical and veterinary
importance. J. Vector Ecology 20(1):
Legner, E. F.. 2000.
Biological control of aquatic Diptera. p. 847-870.
Contributions to a Manual of Palaearctic Diptera,
Vol. 1, Science Herald, Budapest. 978 p.