ARTHROPODA GENERAL CHARACTERS
Cockroaches (or roaches[1][2][3]) are insects of the order Blattodea, which also includes termites. About 30 cockroach species out of 4,600 are associated with human habitats. About five species are well known as pests.
The cockroaches are an ancient group, dating back at least as far as the Carboniferous period, some 320 million years ago. Those early ancestors however lacked the internal ovipositors of modern roaches. Cockroaches are somewhat generalized insects without special adaptations like the sucking mouthparts of aphids and other true bugs; they have chewing mouthparts and are likely among the most primitive of living Neopteran insects. They are common and hardy insects, and can tolerate a wide range of environments from Arctic cold to tropical heat. Tropical cockroaches are often much bigger than temperate species, and, contrary to popular belief, extinct cockroach relatives (Blattoptera) and 'roachoids' such as the Carboniferous Archimylacris and the Permian Apthoroblattina were not as large as the biggest modern species.
Some species, such as the gregarious German cockroach, have an elaborate social structure involving common shelter, social dependence, information transfer and kin recognition. Cockroaches have appeared in human culture since classical antiquity. They are popularly depicted as dirty pests, though the majority of species are inoffensive and live in a wide range of habitats around the world.
Cockroaches are members of the order Blattodea, which includes the termites, a group of insects once thought to be separate from cockroaches. Currently, 4,600 species and over 460 genera are described worldwide.[4][5] The name "cockroach" comes from the Spanish word for cockroach, cucaracha, transformed by 1620s English folk etymology into "cock" and "roach".[6] The scientific name derives from the Latin blatta, "an insect that shuns the light", which in classical Latin was applied not only to cockroaches, but also to mantids.[7][8]
Historically, the name Blattaria was used largely interchangeably with the name Blattodea, but whilst the former name was used to refer to 'true' cockroaches exclusively, the latter also includes the termites. The current catalogue of world cockroach species uses the name Blattodea for the group.[4] Another name, Blattoptera, is also sometimes used to refer to extinct cockroach relatives.[9] The earliest cockroach-like fossils ("blattopterans" or "roachids") are from the Carboniferous period 320 million years ago, as are fossil roachoid nymphs.[10][11][12]
Since the 19th century, scientists believed that cockroaches were an ancient group of insects that had a Devonian origin, according to one hypothesis.[13] Fossil roachoids that lived during that time differ from modern cockroaches in that they had long external ovipositors and are the ancestors of mantises, as well as modern cockroaches. As the body, hind wings and mouthparts are not preserved in fossils frequently, the relationship of these roachoids and modern cockroaches remains disputed. The first fossils of modern cockroaches with internal ovipositors appeared in the early Cretaceous. A recent phylogenetic analysis suggests that cockroaches originated at least in the Jurassic.[13] Common Mesozoic stem-group cockroaches include the Blattulidae and Mesoblattinidae.
The evolutionary relationships of the Blattodea (cockroaches and termites) shown in the cladogram are based on Eggleton, Beccaloni and Inward (2007).[14] The cockroach families Anaplectidae, Lamproblattidae, and Tryonicidae are not shown but are placed within
Dictyo ptera
Blatt odea
Blattoi dea
Termitoidea ( termites)





Termites were previously regarded as a separate order Isoptera to cockroaches. However, recent genetic evidence strongly suggests that they evolved directly from 'true' cockroaches, and many authors now place them as an "epifamily" of Blattodea.[14] This evidence supported a hypothesis suggested in 1934 that termites are closely related to the wood-eating cockroaches (genus Cryptocercus). This hypothesis was originally based on similarity of the
Distribution and habitat[]
Cockroaches are abundant throughout the world and live in a wide range of environments, especially in the tropics and subtropics.[28] Cockroaches can withstand extremely low temperatures, allowing them to live in the Arctic. Some species are capable of surviving temperatures of −122 °C (−188 °F) by manufacturing an antifreeze made out of glycerol.[29] In North America, 50 species separated into five families are found throughout the continent.[28] 450 species are found in Australia.[30] Only about four widespread species are commonly regarded as pests.[31][32]
Cockroaches occupy a wide range of habitats. Many live in leaf litter, among the stems of matted vegetation, in rotting wood, in holes in stumps, in cavities under bark, under log piles and among debris. Some live in arid regions and have developed mechanisms to survive without access to water sources. Others are aquatic, living near the surface of water bodies, including bromeliad phytotelmata, and diving to forage for food. Most of these respire by piercing the water surface with the tip of the abdomen which acts as a snorkel, but some carry a bubble of air under their thoracic shield when they submerge. Others live in the forest canopy where they may be one of the main types of invertebrate present. Here they may hide during the day in crevices, among dead leaves, in bird and insect nests or among epiphytes, emerging at night to feed.[33]
Behavior
A cockroach soon after ecdysis
Cockroaches are social insects; a large number of species are either gregarious or inclined to aggregate, and a slightly smaller number exhibit parental care.[34] It used to be thought that cockroaches aggregated because they were reacting to environmental cues, but it is now believed that pheromones are involved in these behaviors. Some species secrete these in their feces with gut microbial symbionts being involved, while others use glands located on
their mandibles. Pheromones produced by the cuticle may enable cockroaches to distinguish between different populations of cockroach by odor. The behaviors involved have been studied in only a few species, but German cockroaches leave fecal trails with an odor gradient.[34] Other cockroaches follow such trails to discover sources of food and water, and where other cockroaches are hiding. Thus, cockroaches have emergent behavior, in which group or swarm behavior emerges from a simple set of individual interactions.[35]
Daily rhythms may also be regulated by a complex set of hormonal controls of which only a small subset have been understood. In 2005, the role of one of these proteins, pigment dispersing factor (PDF), was isolated and found to be a key mediator in the circadian rhythms of the cockroach.[36]
Pest species adapt readily to a variety of environments, but prefer warm conditions found within buildings. Many tropical species prefer even warmer environments. Cockroaches are mainly nocturnal[37] and run away when exposed to light. An exception to this is the Asian cockroach, which flies mostly at night but is attracted to brightly lit surfaces and pale colors.[38]
Digestive system of Cockroach
Cockroaches would fall under the category of insects of the Blattodea order. Around 4,600 cockroaches are living aside human habitats. The digestion of food would take place in the cavities specialized or combined together.
The Alimentary canal has been divided into three main parts:
Foregut
The alimentary canal starts with the foregut which comprises the mouth and surrounded parts of the mouth. The cavity of mouth is known as pharynx. The foregut extends in the form of the esophagus that has a thin wall (narrow) structure. Further extension of the canal would be called a crop that has a similar structure like the esophagus. The opening for crop called proventriculus/gizzard would be an organ that would be muscular in nature. There is a duo of glands (salivary).
Every salivary gland has branches where various secretions of different branches flow to a combined passage. The receptacle of salivary viz. reservoir that resembles a bladder is in place for both the salivary glands. These are mainly for the storage of the salivary secretions. Both the receptacles have a combined/common passage that is rectangular shaped that would open to the combined salivary passage. The mouth cavity near the labium is opened from the combined salivary passage. The chitin has its lining with the entire foregut. For facilitating food grinding, the chitin creates the proventricular teeth and the plate.
Midgut
Midgut creates real gut viz. Mesenteron and comprises the whole stomach/ventriculus. There are six pairs of gastric (related to the stomach) caecae right at the joint of the gizzard and stomach. At the anterior end of the stomach, these are ordered in a ring-like the style and pouch-like in structure. The anterior lobe of every group of caecae would expand even above the proventriculus whereas posterior lobe would extend to the ventriculus. The digestive juices flow into the stomach owing to the caecae secretion. The midgut is lined by a peritrophic membrane and not by a cuticle. The very same membrane saves the stomach wall from damages and simultaneously fully passable for enzymes and food digested.
Hindgut
This gut is a coil-like structure and consists of the anterior ileum, middle colon, and posterior rectum. The final one viz. the posterior rectum has its opening to the exterior via the anus. It has a lining formed by the cuticle. There are a large number of long tubules also known as Malpighian tubules right at the joint of stomach and ileum.
Digestion Process
Digestion begins first at the mouth where the parts like mandibles and maxillae help to chew the food. The part named salivary carbohydrases digests food to a partial extent. The saliva juice lubricates the food and helps to swallow it. Later the food moves to the esophagus and then onto the crop. This is the point where food in its masticated form is stored temporarily. The next point where the food moves would be at the gizzard where it’s grinding takes place. There is a valve named stomodeal right at the joint of the stomach and gizzard.
The regurgitation of food would be prevented by this valve while ensuring smooth passage of food in the stomach. The food once entering the stomach are treated by the digestive enzymes created by the gastric caecae. The enzymes include invertase, amylase, tryptase, maltase, and lipase. The residual fats, proteins, and carbohydrates would be absorbed here.
From the above-written characteristics, one would be able to understand the complexity of digestion in Cockroaches. The subject has been a point of discussion for students of biology worldwide. Hence this topic should be certainly given its due importance.
NERVOUS SYSTEM OF COCKROACH
The nervous system of cockroach consists of a series of fused, segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side. Three ganglia lie in the thorax, and six in the abdomen. The nervous system of the cockroach is spread throughout the body. The head holds a bit of nervous system while the rest is situated along the ventral (belly-side) part of its body. So, now you understand that if the head of the cockroach is cut off, it will still live for as long as one week. In the head region, the brain is represented by supra-oesophageal ganglion which supplies nerves to antennae and compound eyes. In cockroach, the sense organs are antennae, eyes, maxillary palps, labial palps, and cerci etc. The compound eyes are situated at the dorsal surface of the head. Each eye consists of about 2000 hexagonal ommatidia. With the help of ommatidia, a cockroach can receive several images of an object. This kind is vision is known as a mosaic vision with more sensitivity but less resolution is common during the night (hence called nocturnal vision).
CIRCULATORY SYSTEM OF COCKROACH
The cockroach has an open circulatory system. The blood flows through the body cavity. The circulatory system consists of a heart, anterior aorta, and a system of ill- defined blood spaces known as sinuses.
Heart and Aorta:
The heart of cockroach is an elongated contractile, narrow tube lying along the mid-dorsal
line of thorax and abdomen just beneath the terga. The heart is enclosed in a pericardial sinus,
the wall of which has segmented bundles of alary muscles and a dorsal fenestrated
diaphragm.
The wall of the heart is composed of outer connective tissue and median muscle cells. The
cavity of the heart is lined by the sarcolemma of median muscle cells. The heart consists of
thirteen funnel-shaped and segmentally arranged chambers, each communicating by a
valvular opening with that lying in front of it (Fig. 2.65).
The hinder end of each chamber has a pair of minute, lateral and valvular openings called
ostia, which allows the flow of blood from the pericardium into the heart only and not in
reverse direction. In each segment, heart sends a pair of ex-current arteries.
The heart is closed behind but is continued forward as a short and narrow tube without ostia
called the aorta. This aorta and segmental arteries finally open within the haemocoelic
The body cavity of cockroach is not a true coelom but a haemocoel containing blood
(haemolymph).
The diaphragm or the dorsal fenestrated partition divides the haemocoel into three sinuses:
(i) The dorsal or pericardial sinus surrounding the heart, aorta and alary muscles,
(ii) The middle or perivisceral sinus containing the alimentary canal (Fig. 2.66) and
(iii) The ventral sternal or perineural sinus enclosing the ventral nerve cord. It also extends
into the legs as septa, dividing the cavity of each leg into two sinuses, one for the outward
and the other for the inward flow of blood. The diaphragm being perforated, permits the
blood to flow from one sinus into another.
Circulating Fluid in Cockroach:
Haemolymph:
In cockroach, the circulating fluid does not always flow through the vessels, rather comes in
direct contact with the tissues while flowing in the haemocoel.
So the ‘blood’ of cockroach is both blood as well as lymph and is therefore, called
haemolymph. It is colourless, as it lacks the respiratory pigment haemoglobin and does not
take part in respiration. It consists of a clear fluid plasma in which are suspended nucleated
cells or haemocytes.
The plasma contains various inorganic ions like sodium, potassium, calcium; organic com-
pounds like, citrate; amino acids viz. alanine, cystine, glycine, tyrosine, valine etc.; enzymes
like chitinase and glucosidase; carbohydrates; lipids and uric acid.
The plasma serves primarily as a means for:
(i) Transportation of dissolved substances like food and wastes round the body,
(ii) Transmission of hydrostatic pressure from one end of the body to the other,
(iii) Reservoir of food as well as water and
(iv) It also helps in hatching of eggs, moulting and in expansion of wings.
Haemocytes:
The structure and function of the haemocytes of different insects including cockroach have
been reviewed by different workers. However, the following haemocytes (Fig. 2.67) are most
commonly present in cockroach haemolymph.
1. Prohaemocytes:
Small round cells with large nucleus and thin agranular cytoplasm. These cells divide to give
rise to other kinds of haemocytes.
2. Plasmocytes:
Large amoeboid cells with pseudopodia, large nucleus and large mass of a granular cytoplasm.
3. Granulocytes:
4. Cystocytes/Coagulocytes:
Cells with small nucleus and a pale hyaline cytoplasm with black granules (Fig. 2.67). The total
number of cells in the haemolymph of adult Periplaneta is about 15,00,000 though the
number obviously depends on the volume of haemolymph which is about 15.7-17.5 per cent
of body weight. Haemocytes play significant role in the physiology and survival of
cockroaches.
(ii) Encapsulation of metazoan parasites,
(v) Wound repair,
(viii) Coagulation of haemolymph.
Mechanism of Circulation in Cockroach:
The contraction of alary muscles enlarges the pericardial space so that the haemolymph flows
into it from the underlying perivisceral sinus. When the alary muscles relax, the haemolymph
is forced through the ostia into the heart. As the heart relaxes during diastole (Fig. 2.68) the
tension of the ligament stretches out the walls of heart so that the haemolymph flows into
the organs; anteriorly into the head.
It then passes back from the haemocoel of head into that of the thorax and abdomen and
enters the pericardium. In addition to alary muscles, contraction of dorsal diaphragm also
helps in rapid circulation of haemolymph. The heart beats at a rate of 100-200 per minute at
27°C. A complete cycle of circulation of haemolymph through the body takes 20-30 minutes.
Male Reproductive Organs of Cockroach:
The male reproductive system of cockroach consists of a pair of testes, vasa deferentia, an
ejaculatory duct, utricular gland, phallic gland and the external genitalia.
(i) Testes:
There is a pair of three-lobed testes lying dorsolaterally in the 4th and 5th abdominal
segments, being embedded in the fat body. The testes are well developed and elaborate
structures in young cockroach and they are full of sperms. The testes become non-functional
and reduced in old adults but some sperms may still be found in them.
(ii) Vasa Deferentia:
From each testis arises a thin thread-like, white vasa deferens. Both the vasa deferentia pass
backwards almost to the posterior end of abdomen and then bend forwards to meet in the
middle and open into an ejaculatory duct.
(iii) Ejaculatory Duct:
The ejaculatory duct is an elongated wide median duct which runs backwards in the abdomen
and opens out by male gonopore situated ventral to the anus.
(iv) Utricular or Mushroom-shaped Gland:
It is a large accessory reproductive gland, whitish in colour and situated at the junction of vasa
deferentia with the ejaculatory duct. It has a mass of glandular tubules of three kinds, the
peripheral long tubules or utriculi majores, the central tubules are small short tubules or
utriculi breviores and behind the short central tubules are some short but more bulbous
tubules forming the seminal vesicles filled with sperms.
(v) Phallic or Conglobate Gland:
It is a long and club-shaped accessory gland. Its anterior broader end lies in the 6th segment
slightly to the right of the nerve cord. It narrows posteriorly into a tubular structure and finally
tapers to open by a separate aperture located close to the male gonopore at the hind end of
the body.
Some chitinous asymmetrical structures are found surrounding the male gonopore at the end
of the abdomen. These are three phallomeres or male gonapophyses which constitute the
external genitalia.
Right Phallomere:
It is mid-dorsal in position. It has two chitinous but membranous horizontal opposing plates
and a broad serrate lobe with a saw- toothed edge and two large teeth, and at its posterior
side it has a sickle-shaped hook.
Left Phallomere:
It has a broad base from which several structures arise, on the extreme left is a long slender
arm with a curved hook called titillator, next to the titillator is a shorter and broader arm
ending in a black hammer-like head called pseudopenis.
Close to the pseudopenis are three small soft lobes, one of which bears a hook and is called
an asperate lobe. The duct of the phallic gland traverses the left phallomere and opens
between the asperate lobe and pseudopenis.
Ventral Phallomere:
It is very simple in structure and lies partly below the right phallomere. It has a large brown
plate and bears the male gonopore.
Spermatophore:
The sperms produced from testes, while the cockroach is still young, are brought by the vasa
deferentia into the seminal vesicles for storage. The sperms in the seminal vesicles are glued
together in the form of bundles called spermatophores. Actually, the spermatophores are
discharged by the male during copulation.
A spermatophore is pear-shaped about 13 mm in diameter and its wall has three layers.
Its innermost layer is first formed by the milky secretion secreted from the long peripheral
tubules of the utricular gland. This layer then receives bundled sperms from seminal vesicle
and a liquid from the short tubules of the utricular gland. Then this inseminated layer passes
down the ejaculatory duct and it receives the second layer from the cells of ejaculatory duct.
During mating, the two layered spermatophore, thus, formed is attached to the spermathecal
aperture of the female and then the secretion of phallic gland is poured over it which hardens
to form the third and outermost layer of the spermatophore (Fig. 73.34).
Female Reproductive Organs of Cockroach:
The female reproductive system of cockroach (Fig. 73.35) consists of a pair of ovaries, vagina,
genital pouch, collaterial glands, spermathecae and the external genitalia.
(i) Ovaries:
There are two large, light yellow- coloured ovaries lying laterally in the segment 4th, 5th, 6th,
embedded in the fat body. Each ovary is formed of a group of eight ovarian tubules or
ovarioles containing a chain of developing ova. An ovariole is made up of an epithelial layer
resting on a basement membrane and enclosed externally in a connective tissue coat.
However, an ovariole from in front to backwards consists of the following zones:
(i) Suspensory filament, it is thin, thread-like continuation of the connective tissue layer and
provides attachment of the ovariole to the dorsal body wall and, thus, it serves to suspend
the ovariole in the haemocoel.
(ii) Zone of germarium, it follows the terminal filamentous zone and consists of germ cells or
oogonia and mature into oocytes and pushed downwards.
(iii) Vitellarium, this zone receives the oocytes from the zone of germarium one by one and
constitutes the largest part of the ovariole, the oocytes become enclosed in a follicle of
epithelium and increase progressively in size towards the posterior end which gives it beaded
appearance.
(iv) Egg chamber, the vitellarium opens posteriorly into a small, thick, oval egg chamber which
contains a single large mature ovum at a time.
(v) Stalk or pedicel, the egg chamber continues posteriorly into thin-walled, hollow stalk which
opens into the lateral oviduct.
Oviducts:
The stalk of all eight ovarioles on one side join to form an oviduct which is lateral, small and
with muscular wall.
(ii) Vagina:
Both the lateral oviducts unite to form a broad median common oviduct called vagina. The
vagina opens by the female gonopore into the genital chamber.
(iii) Genital Pouch:
It is a large boat-shaped structure whose floor is formed by the 7th sternite, roof and sides
are formed by the 8th and 9th sternites. The genital pouch can be divided into a genital
chamber into which vagina opens and an oothecal chamber where oothecae are formed. The
genital chamber also receives the accessory reproductive glands.
The female gonopore is an aperture in the 8th sternum, which lies inside the genital chamber
inflected above the 7th sternite. The 7th sternite is also produced backwards into two large
oval gynovalvular plates or apical lobes. The genital pouch is also referred to as gynatrium.
(iv) Collaterial Glands:
There is a pair of white much branched collaterial glands, the left is much larger than the right.
Both these glands continue as collaterial ducts which join to form a common duct which opens
into the dorsal side of the genital chamber. These are the accessory reproductive glands.
(v) Spermathecae:
These are a pair of club-shaped, unequal-sized, one spermathecae being larger than the other,
structures. Both the spermathecae unite to form a short common duct which opens into the
genital chamber on a small spermathecal papilla. Some workers claim that there is a single
spermatheca and it has a lateral caecum.
(vi) External Genitalia of Female:
These lie concealed inside the gynatrium. They consist of an ovipositor formed by two
gonapophyses. The ovipositor lies above and behind the gonopore, it is short and has three
pairs of elongated processes, a pair of long thick arms lying dorsally and enclosing two pairs
of slender tapering arms.
These two pairs of arms arise from a common base and they constitute the posterior
gonapophyses, they belong to the 9th abdominal segment and are joined to the 9th tergum.
below the posterior gonapophyses and constitute the anterior gonapophyses. These belong
to the 8th abdominal segment and are attached to the outer margins of 8th tergum. The
ovipositor is used only to conduct fertilised eggs to the oothecal chamber.
DIFFERENT TYPE OF MOUTH PARTS IN INSECTS
Insects have a range of mouthparts, adapted to particular modes of feeding. The earliest insects had chewing mouthparts. Specialization has mostly been for piercing and sucking, although a range of specializations exist, as these modes of feeding have evolved a number of times (for example, mosquitoes and aphids (which are true bugs) both pierce and suck, however female mosquitoes feed on animal blood whereas aphids feed on plant fluids. In this page, the individual mouthparts are introduced for chewing insects. Specializations are generally described thereafter.
The development of insect mouthparts from the primitive chewing mouthparts of a
grasshopper in the centre (A), to the lapping type (B) of a bee, the siphoning type (C) of a
butterfly and the sucking type (D) of a female mosquito. Legend: a, antennae; c, compound
eye; lb, labium; lr, labrum; md, mandibles; mx, maxillae hp hypopharynx.…
Chewing insects[]
The trophi, or mouthparts of a locust, a typical chewing insect:
1 Labrum
2 Mandibles;
3 Maxillae
4 Labium
5 Hypopharynx
Examples of chewing insects include dragonflies, grasshoppers and beetles. Some insects do not have chewing mouthparts as adults but do chew solid food when they feed while they still are larvae. The moths and butterflies are major examples of such adaptations.
The mandibles of a bull ant
European honeybee (Apis mellifera) lapping mouthparts, showing labium and maxillae
A chewing insect has a pair of mandibles, one on each side of the head. The mandibles are caudal to the labrum and anterior to the maxillae. Typically the mandibles are the largest and most robust mouthparts of a chewing insect, and it uses them to masticate (cut, tear, crush, chew) food items. Two sets of muscles move the mandibles in the coronal plane: abductor muscles move insects' mandibles apart (laterally); adductor muscles bring them together (medially). This they do mainly in opening and closing their jaws in feeding, but also in using the mandibles as tools, or possibly in fighting; note however, that this refers to the coronal plane of the mouth, not necessarily of the insect's body, because insects' heads differ greatly in their orientation.
In carnivorous chewing insects, the mandibles commonly are particularly serrated and knife- like, and often with piercing points. In herbivorous chewing insects mandibles tend to be broader and flatter on their opposing faces, as for example in caterpillars.
In males of some species, such as of Lucanidae and some Cerambycidae, the mandibles are modified to such an extent that they do not serve any feeding function, but are instead used to defend mating sites from other males. In some ants and termites, the mandibles also serve a defensive function (particularly in soldier castes). In bull ants, the mandibles are elongate and toothed, used both as hunting and defensive appendages. In bees, that feed primarily by
Maxilla[]
Situated beneath (caudal to) the mandibles, paired maxillae manipulate and, in chewing insects, partly masticate, food. Each maxilla consists of two parts, the proximal cardo (plural cardines), and distal stipes (plural stipites). At the apex of each stipes are two lobes, the inner lacinia and outer galea (plurals laciniae and galeae). At the outer margin, the typical galea is a cupped or scoop-like structure, located over the outer edge of the labium. In non-chewing insects, such as adult Lepidoptera, the maxillae may be drastically adapted to other functions.
Unlike the mandibles, but like the labium, the maxillae bear lateral palps on their stipites. These palps serve as organs of touch and taste in feeding and in the inspection of potential foods and/or prey.
In chewing insects, adductor and abductor muscles extend from inside the cranium to within the bases of the stipites and cardines much as happens with the mandibles in feeding, and also in using the maxillae as tools. To some extent the maxillae are more mobile than the mandibles, and the galeae, laciniae, and palps also can move up and down somewhat, in the sagittal plane, both in feeding and in working, for example in nest building by mud-dauber wasps.
Maxillae in most insects function partly like mandibles in feeding, but they are more mobile and less heavily sclerotised than mandibles, so they are more important in manipulating soft, liquid, or particulate food rather than cutting or crushing food such as material that requires the mandibles to cut or crush.
Like the mandibles, maxillae are innervated by the subesophageal ganglia.
Labium
The labium typically is a roughly quadrilateral structure, formed by paired, fused secondary maxillae.[1] It is the major component of the floor of the mouth. Typically, together with the maxillae, the labium assists manipulation of food during mastication.
Dragonfly nymph feeding on fish that it has caught with its labium and snatched back to the
other mouthparts for eating. The labium is just visible from the side, between the front pairs
of legs
The role of the labium in some insects however, is adapted to special functions; perhaps the most dramatic example is in the jaws of the nymphs of the Odonata, the dragonflies and damselflies. In these insects, the labium folds neatly beneath the head
and thorax, but the insect can flick it out to snatch prey and bear it back to the head, where the chewing mouthparts can demolish it and swallow the particles.[2]
The labium is attached at the rear end of the structure called cibarium, and its broad basal portion is divided into regions called the submentum, which is the proximal part, the mentum in the middle, and the prementum, which is the distal section, and furthest anterior.
The prementum bears a structure called the ligula; this consists of an inner pair of lobes called glossae and a lateral pair called paraglossae. These structures are homologous to the lacinia and galea of maxillae. The labial palps borne on the sides of labium are the counterparts of maxillary palps. Like the maxillary palps, the labial palps aid sensory function in eating. In many species the musculature of the labium is much more complex than that of the other jaws, because in most, the ligula, palps and prementum all can be moved independently.
The labium is innervated by the sub-esophageal ganglia.[3][4][5]
In the honey bee, the labium is elongated to form a tube and tongue, and these insects are classified as having both chewing and lapping mouthparts. [6]
The wild silk moth (Bombyx mandarina) is an example of an insect that has small labial palpi and no maxillary palpi.[7]
Hypopharynx[]
The hypopharynx is a somewhat globular structure, located medially to the mandibles and the maxillae. In many species it is membranous and associated with salivary glands. It assists in swallowing the food. The hypopharynx divides the oral cavity into two parts: the cibarium or dorsal food pouch and ventral salivarium into which the salivary duct opens.
Siphoning insects[]
An Australian painted lady with its proboscis extended during feeding
This section deals only with insects that feed by sucking fluids, as a rule without piercing their food first, and without sponging or licking. Typical examples are adult moths and butterflies. As is usually the case with insects, there are variations: some moths, such as species of Serrodes and Achaea do pierce fruit to the extent that they are regarded as serious orchard
pests.[8] Some moths do not feed after emerging from the pupa, and have greatly reduced, vestigial mouthparts or none at all. All but a few adult Lepidoptera lack mandibles (the superfamily known as the mandibulate moths have fully developed mandibles as adults), but also have the remaining mouthparts in the form of an elongated sucking tube, the proboscis.
Butterfly proboscis, showing the structure of the two galeae that comprise it
Proboscis[]
The proboscis, as seen in adult Lepidoptera, is one of the defining characteristics of the morphology of the order; it is a long tube formed by the paired galeae of the maxillae. Unlike sucking organs in other orders of insects, the Lepidopteran proboscis can coil up so completely that it can fit under the head when not in use. During feeding, however, it extends to reach the nectar of flowers or other fluids. In certain specialist pollinators, the proboscis may be several times the body length of the moth.
Piercing and sucking insects[]
A number of insect orders (or more precisely families within them) have mouthparts that pierce food items to enable sucking of internal fluids. Some are herbivorous, like aphids and leafhoppers, while others are carnivorous, like assassin bugs and mosquitoes (females only).
Proboscis[]
The defining feature of the order Hemiptera is the possession of mouthparts where the mandibles and maxillae are modified into a proboscis, sheathed within a modified labium, which is capable of piercing tissues and sucking out the liquids. For example, true bugs, such as shield bugs, feed on the fluids of plants. Predatory bugs such as assassin bugs have the same mouthparts, but they are used to pierce the cuticles of captured prey.
Stylet[]
A mosquito biting a human finger
In female mosquitoes, all mouthparts are elongated. The labium encloses all other mouthparts like a sheath. The labrum forms the main feeding tube, through which blood is sucked. Paired mandibles and maxillae are present, together forming the stylet, which is used to pierce an animal's skin. During piercing, the labium remains outside the food item's skin, folding away from the stylet. Saliva containing anticoagulants, is injected into the food item and blood sucked out, each through different tubes.
Sponging insects[]
Proboscis of the fly (Gonia capitata): note also the protruding labial palps.
Labellum[]
The housefly is a typical sponging insect. The labellum's surface is covered by minute food channels, formed by the interlocking elongate hypopharynx and epipharynx, forming a proboscis used to channel liquid food to the oesophagus. The food channel draws liquid and liquified food to the oesophagus by capillary action. The housefly is able to eat solid food by secreting saliva and dabbing it over the food item. As the saliva dissolves the food, the solution is then drawn up into the mouth as a liquid.[9]
ECONOMIC IMPORTANCE OF INSECTS
A. Beneficial Insects:
Insects which produce honey, wax, lac, dyes and silk are commercially beneficial. Some insects
are very helpful in destroying injurious insects.
1. Commercial Products:
Apis, the honeybees produce millions of tons of honey every year, it also gives bees wax from
its combs.
Benefits of bees are cosmopolitan, not only in producing honey and wax, but also in bringing
about cross-pollination of many fruits and flowers without which these plants could not exist.
protective covering by females, shellac is made from lac in India.
Dactylopius, the cochineal insect of Mexico is found on cacti, dried bodies of females of this
scale insect are used for making cochineal dyes. Bombyx and Eupterote are silk moths, they
are reared in India, China, Japan and Europe, their larvae called silk worms spin cocoon of raw
silk, the silk fibre is reeled off and used for making silk.
In Asiatic countries over 25 million kilograms of silk are produced annually. Dried elytra of two
beetles, Lytta and Mylabris are used for making cantharidin, a powerful aphrodisiac.
The larvae of two flies, Lucilla and Phormia are used in healing such wounds of bones which
do not respond to medicines, the larvae are put in wounds of bones and bone marrow, they
clear away suppurating and dead tissues, prevent bacterial growth and excrete allantoin
which heals the wounds.
2. Useful Predaceous Insects:
Some insects are predaceous, they feed upon and destroy a large number of injurious insects.
Stagomantis, a mantis is voracious, it feeds on flies, grasshoppers and caterpillars, some of
which are injurious to crops. The larvae and adults of Chilomenes, a lady-bird beetle, feed on
aphids which infect cotton plants.
Novius, a lady-bird bettle, destroys scale worms which are pests of orange and lemon trees.
Epicauta is a blister beetle, it deposits eggs where locusts occur, the larvae on hatching enter
egg capsules of locusts and eat up masses of eggs. Calasoma, a ground beetle preys upon
many kinds of lepidopterous larvae which destroy cereals and cotton.
3. Beneficial Parasitic Insects:
Some insects parasitise injurious insects, they usually lay eggs in the bodies of larvae and
adults of harmful insects; the young on hatching from eggs finally kill their hosts. The larvae
of Tachina and related flies are parasites of injurious lepidopterous larvae, such as army-
worms which are injurious to cereals.
Larvae of hymenopteran flies and carnivorous wasps devour aphids in large numbers. Chalcids
and ichneumon flies are parasitic, laying eggs in cocoon and larvae of phytophagous
Lepidoptera. Apanteles, a hymenopteran fly lays eggs in army-worms and boll worms, the
parasitic larvae gnaw their way through the skin of the host.
4. Scavengers:
Some insects are scavengers, they eat up dead animal and vegetable matter, thus, they
prevent decay. Some ants and larvae of some flies can devour entire animal carcasses.
B. Injurious Insects:
Compared with beneficial insects the number of injurious insects is very large.
1. Disease Transmitting Insects:
Many types of mosquitoes, flies, fleas, lice and bugs transmit diseases to man and domestic
animals, they have been described earlier in insects and diseases.
2. Household Insects:
Human food is spoiled by cockroaches, ants, flies and weevils. Tinea, Teniola and Trichophaga
are clothes moths, they lay eggs on warm clothes, the larvae on hatching eat and destroy
clothes, they also feed on furs, carpets and dry fruits. Anthrenus is a carpet beetle, it is a
scavenger eating decaying animal matter, but its larvae destroy carpets and preserved
biological specimens.
Tenebrio is the mealworm beetle, its larvae are mealworms, they eat meal, flour and stored
grains, such as rice. Lepisma, the silver fish and Liposcelis, the book louse live in and destroy
books and old manuscripts. Termites, the white ants cause untold destruction of books,
carpets, furniture and wood-work of buildings.
Glossina, the tsetse fly transmits Trypanosoma brucei which causes nagana in horses. Tabanus
and Stomoxys, the blood sucking flies inject Trypanosoma evansi into horses and cattle which
causes surra in India.
The larvae of Hypoderma, the warble fly bore below the skin of oxen and make holes for
breathing, then they pass through the gullet and again pierce the skin on the sides of the spine
to form swellings, they not only injure the hide but also reduce the meat and milk supply.
Gasterophilus, the bot-fly lays eggs on hair of horse, the larvae enter the stomach in large
numbers. Melophagus, the sheep tick and Hippobosca, the forest fly of cattle and horses suek
blood of their hosts and often cause haemorrhage. Menopon, the chicken louse sucks blood
and causes destruction of fowls.
4. Injurious to Crops:
Many insects damage forest trees, growing farm crops, fruits and stored grain, the damage
they cause annually runs into millions of rupees.
The number of such insects is innumerable, they are mostly Lepidoptera, Coleoptera, Diptera
and Hemiptera. Euproctis, the brown tail moth and Lymantria, the gipsy moth are serious
pests of shade and foliage trees, their larvae are a menace and destroy forest trees. Myetiola,
the Hessian fly is a small sized midge, its larvae damage wheat plants.
The larvae of two Lepidoptera Chilo in India, and Diatraea in America bore into stems of sugar-
cane and cause a great deal of damage. Pyrilla, a hemipteran sugar-cane leaf hopper sucks
the juice of sugar-cane, both as adult and nymph, causing great loss of sugar.
Pyrausta is a moth found all over the world, but specially abundant in the tropics, its larvae
known as corn borers are notorious for boring into stems and fruits of corn (maize).
Nephotettix, the Indian rice leaf-hopper and Leptocorisa, the oriental pest of rice and millet
are Hemiptera, they attack rice in very large number eating the leaves and ears.
The larvae of Schoenobius, a moth bore into the stems of rice plants in India, they kill the
plants. Nymphs and adults of Hieroglyphus, an orthopteran eat up the growing shoots of rice
plants, thus, preventing formation of grain.
Dysdercus, the Indian cotton bug, Oxycarenus, the Egyptian cotton bug, and Anthonomous
the cotton-boll weevil are very injurious to cotton, they stain and destroy cotton- bolls, Aphis,
a hemipteran is a serious cotton pest in India, the pests often attack cotton plants in large
numbers causing the plants to wilt and die.
The larvae of two Lepidoptera, Agrotis and Gnorimoschema are potato cut-worms in India,
the former feeds on potato leaves and cuts off the stems, while the larvae of the latter eat
the potatoes in the field and stores, larvae also attack tobacco and tomatoes. Larvae of
Agrotis are also destructive to peas, cabbage, tobacco, ground nuts, wheat and cauliflowers.
The larvae of some Coleoptera are called wire-worms, such as Agriotis and Limonius, they are
root-feeders and are extremely destuctive to cereals, root crops and grasses. Many insects
and their larvae destroy vegetables in India.
Siphocoryne is an aphis which feeds on cabbage leaves; Anasa, the squash bug is destructive
to cucurbitaceous plants; Earias the spotted bollworm destroys ladyfingers; Aulacophora, the
red beetle feeds on pumpkins; the larvae of Bruchus, a beetle bore into pods of beans and
peas killing the seed.
Many insects attack fruit trees, they damage roots, trunks, stems, leaves, inflorescence and
fruit. Drosicha, a mealy bug causes destruction of mangoes, plums, papaya, jack fruit, pears
and citrus fruits in India. The nymphs and adults of Ideocerus, a mango leaf hopper attack the
inflorescence and suck the sap, thus, they cause tremendous damage by preventing
formation of mango fruit.
The laryae of Contarinia fly feed on young pears which soon decay. Psylla, an apple bug, lays
eggs on apple and pear tree, the nymphs on hatching damage the blossom and shoots; the
larvae of Anthonomus, a beetle also destroy apple blossoms and prevent formation of the
fruit. Nysius, a bug is very destructive to several kinds of fruit trees.
Many moths, caterpillars and beetle cause a great deal of damage to stored grains: two
beetles Tenebrio and Tribolium have similar habits and are commonly found in stores and
granaries, the former is found in all stages in meal, flour and stored goods, its larvae are
known as meal worms. Tribolium eats stored wheat and grain. Calandra, a weevil bores