|
Arthropoda:
Insecta
HYMENOPTERA
(Contact)
Please CLICK on
image & underlined links to view:
[Also See: ID Keys: Great Britain, Palearctic
Region, European Russia-1]
GENERAL CHARACTERISTICS OF THE HYMENOPTERA
 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
anterior tibiae.
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
plant tissues.
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 persist.
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
nutrition (Borradaile & 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
And 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 reached.
The 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 food.
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 food.
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
length.
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
the colony.
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).
= = = = = = = = = = = = = = = = = = = =
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 family.
---------------------------------------
Subdivisions and
Classification
There are two
suborders: Symphyta (Chalastogastra)
are the sawflies and Apocrita (Clistogastra) are all other groups.
The Symphyta 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.
The Apocrita 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.
HYMENOPTERA 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.
= = = = = = = = = = = =
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):
59-120.
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.
|
