Insect mouthparts

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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. Evolution insect mouthparts coloured derivate.png
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.

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.

Contents

Evolution

Like most external features of arthropods, the mouthparts of hexapoda are highly derived. Insect mouthparts show a multitude of different functional mechanisms across the wide diversity of species considered insects. Certainly it is common for significant homology to be conserved, with matching structures formed from matching primordia, and having the same evolutionary origin. On the other hand, even structures that physically are almost identical, and share almost identical functionality as well, may not be homologous; their analogous functions and appearance might be the product of convergent evolution.

Chewing insects

The trophi, or mouthparts of a locust, a typical chewing insect:
1 Labrum
2 Mandibles;
3 Maxillae
4 Labium
5 Hypopharynx Comparative zoology, structural and systematic - for use in schools and colleges (1883) (20661526772).jpg
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.

Mandible

The mandibles of a bull ant Bullant head detail.jpg
The mandibles of a bull ant
European honeybee (Apis mellifera) lapping mouthparts, showing labium and maxillae European Honeybee (Apis mellifera) lapping mouthparts, showing labium and maxillae..jpg
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 use of a proboscis, the primary use of the mandibles is to manipulate and shape wax, and many paper wasps have mandibles adapted to scraping and ingesting wood fibres.

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 sub-esopharyngeal 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 labrum 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 Libellenlarve frisst Fisch.jpg
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 Australian painted lady feeding closeup.jpg
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 Butterfly proboscis (galea).jpg
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 Mosquito bite4.jpg
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. Tachina fly Gonia capitata feeding honey.jpg
Proboscis of the fly ( Gonia capitata ): note also the protruding labial palps.

Labellum

The housefly is the typical sponging insect. The labium gives the description, being articulate and possessing at its end a sponge-like labellum. Paired mandibles and maxillae are present, but much reduced and non-functional. 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]

Related Research Articles

Mosquito Family of flies

Mosquitoes are a group of about 3,500 species of small insects that are flies. Within Diptera they constitute the family Culicidae. The word "mosquito" is Spanish for "little fly". Mosquitoes have a slender segmented body, one pair of wings, one pair of halteres, three pairs of long hair-like legs, and elongated mouthparts.

Hemiptera Order of insects often called bugs

The Hemiptera or true bugs are an order of insects comprising some 50,000 to 80,000 species of groups such as the cicadas, aphids, planthoppers, leafhoppers, and shield bugs. They range in size from 1 mm (0.04 in) to around 15 cm (6 in), and share a common arrangement of sucking mouthparts. The name "true bugs" is sometimes limited to the suborder Heteroptera. Many insects commonly known as "bugs" belong to other orders; for example, the lovebug is a fly and the May bug and ladybug are beetles.

Proboscis an elongated appendage from the head of an animal, either a vertebrate or an invertebrate

A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elongated nose or snout.

Reduviidae Family of insects

The Reduviidae are a large cosmopolitan family of the order Hemiptera. They are unusual among the Hemiptera because almost all are terrestrial ambush predators. The main examples of nonpredatory Reduviidae are some blood-sucking ectoparasites in the subfamily Triatominae. Though spectacular exceptions are known, most members of the family are fairly easily recognizable; they have a relatively narrow neck, sturdy build, and formidable curved proboscis. Large specimens should be handled with caution, if at all, because they sometimes defend themselves with a very painful stab from the proboscis.

Decapod anatomy The entire structure of a decapod crustacean

The decapod crustacean, such as a crab, lobster, shrimp or prawn, is made up of 20 body segments grouped into two main body parts, the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various groups these may be reduced or missing. They are, from head to tail:

Asilidae family of insects

The Asilidae are the robber fly family, also called assassin flies. They are powerfully built, bristly flies with a short, stout proboscis enclosing the sharp, sucking hypopharynx. The name "robber flies" reflects their notoriously aggressive predatory habits; they feed mainly or exclusively on other insects and as a rule they wait in ambush and catch their prey in flight obtaining sufficient nourishment.

Glossary of entomology terms Wikimedia glossary list article

This glossary of entomology describes terms used in the formal study of insect species by entomologists.

Mandible (insect mouthpart) part of the mouth of an insect

Insect mandibles are a pair of appendages near the insect’s mouth, and the most anterior of the three pairs of oral appendages. Their function is typically to grasp, crush, or cut the insect’s food, or to defend against predators or rivals. Insect mandibles, which appear to be evolutionarily derived from legs, move in the horizontal plane unlike those of vertebrates, which appear to be derived from gill arches and move vertically.

Arthropod mouthparts

The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired appendages, which in ancestral forms would have appeared more like legs than mouthparts. In general, arthropods have mouthparts for cutting, chewing, piercing, sucking, shredding, siphoning, and filtering. This article outlines the basic elements of four arthropod groups: insects, myriapods, crustaceans and chelicerates. Insects are used as the model, with the novel mouthparts of the other groups introduced in turn. Insects are not, however, the ancestral form of the other arthropods discussed here.

Spider anatomy

The anatomy of spiders includes many characteristics shared with other arachnids. These characteristics include bodies divided into two tagmata, eight jointed legs, no wings or antennae, the presence of chelicerae and pedipalps, simple eyes, and an exoskeleton, which is periodically shed.

Mouth first portion of the alimentary canal that receives food

In animal anatomy, the mouth, also known as the oral cavity, buccal cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on the outside by the lips and inside by the pharynx and containing in higher vertebrates the tongue and teeth. This cavity is also known as the buccal cavity, from the Latin bucca ("cheek").

Mandible (arthropod mouthpart) Pair of mouthparts used either for biting or cutting and holding food

The mandible of an arthropod is a pair of mouthparts used either for biting or cutting and holding food. Mandibles are often simply referred to as jaws. Mandibles are present in the extant subphyla Myriapoda, Crustacea and Hexapoda. These groups make up the clade Mandibulata, which is currently believed to be the sister group to the rest of arthropods, the clade Arachnomorpha.

Maxilla (arthropod mouthpart)

In arthropods, the maxillae are paired structures present on the head as mouthparts in members of the clade Mandibulata, used for tasting and manipulating food. Embryologically, the maxillae are derived from the 4th and 5th segment of the head and the maxillary palps; segmented appendages extending from the base of the maxilla represent the former leg of those respective segments. In most cases, two pairs of maxillae are present and in different arthropod groups the two pairs of maxillae have been variously modified. In crustaceans, the first pair are called maxillulae.

External morphology of Lepidoptera The external features of butterflies and moths are described and explained.

The external morphology of Lepidoptera is the physiological structure of the bodies of insects belonging to the order Lepidoptera, also known as butterflies and moths. Lepidoptera are distinguished from other orders by the presence of scales on the external parts of the body and appendages, especially the wings. Butterflies and moths vary in size from microlepidoptera only a few millimetres long, to a wingspan of many inches such as the Atlas moth. Comprising over 160,000 described species, the Lepidoptera possess variations of the basic body structure which has evolved to gain advantages in adaptation and distribution.

Insect morphology study of the structure and major workings of the insect body

Insect morphology is the study and description of the physical form of insects. The terminology used to describe insects is similar to that used for other arthropods due to their shared evolutionary history. Three physical features separate insects from other arthropods: they have a body divided into three regions, have three pairs of legs, and mouthparts located outside of the head capsule. It is this position of the mouthparts which divides them from their closest relatives, the non-insect hexapods, which includes Protura, Diplura, and Collembola.

Paraneoptera superorder of insects

Paraneoptera is a monophyletic superorder of insects which includes four orders, the bark lice, true lice, thrips, and hemipterans, the true bugs. The mouthparts of the Paraneoptera reflect diverse feeding habits. Basal groups are microbial surface feeders, whereas more advanced groups feed on plant or animal fluids.

<i>Platymeris laevicollis</i> species of insect

Platymeris laevicollis is a venomous predatory true bug from central Africa that can be found in forests, scrublands, grasslands, and croplands. They are efficient predators and are used by farmers on coconut plantations to control herbivorous pests such as the rhinoceros beetle. As a true bug of the order Hemiptera, it has needle-like mouth parts designed for sucking juices out of plants or other insects instead of chewing. P. laevicollis has sharp stylets in its proboscis or rostrum used to pierce the exoskeleton of its prey. Saliva is then injected into the prey which liquifies its tissues,and the rostrum is then used to suck out the digested fluids. If disturbed, it is capable of a defensive bite considered to be more painful than a bee sting.

Insects are among the most diverse groups of animals on the planet, including more than a million described species and representing more than half of all known living organisms. The number of extant species is estimated at between six and ten million, found in nearly all environments, although only a small number of species occur in the oceans. This large extant means that the dietary habits of taxa include a large variety of behaviors.

Harald W. Krenn is an Austrian biologist and a professor for integrative zoology at the Fakultät für Lebenswissenschaften at the University of Vienna.

Labellum (insect anatomy)

In entomology, the term labellum has been applied variously and in partly contradictory ways. One usage is in referring to a prolongation of the labrum that covers the base of the rostrum in certain Coleoptera and Hemiptera.

References

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  2. Head, Mandibles, and unusual Labium of Dragonfly Nymph (viewed from below) [ unreliable source? ]
  3. Insect Mouthparts
  4. Insect mouthparts - Amateur Entomologists' Society (AES)
  5. Structure and function of insect mouthparts
  6. "Hymenoptera: ants, bees and wasps", CSIRO, retrieved 8 April 2012
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