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 mouthparts that may vary greatly across insect species, as they are adapted to particular modes of feeding. The earliest insects had chewing mouthparts. Most specialisation of mouthparts are for piercing and sucking, and this mode of feeding has evolved a number of times independently. For example, mosquitoes (which are true flies) and aphids (which are true bugs) both pierce and suck, though female mosquitoes feed on animal blood whereas aphids feed on plant fluids.

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 insect species. It is common for significant homology to be conserved, with matching structures forming from matching primordia, and having the same evolutionary origin. However, even if structures are almost physically and functionally identical, they 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 chew solid food in their larval phase. 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 of the mouth: abductor muscles move insects' mandibles apart (laterally); adductor muscles bring them together (medially). They do this mainly in opening and closing their jaws in feeding, but also in using the mandibles as tools, or possibly in fighting.

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 the 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 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. 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] [ unreliable source? ]

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

Butterflies coil the proboscis when not feeding. Proboscis DSC 0250.jpg
Butterflies coil the proboscis when not 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.

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 female mosquitoes.

Stylets

Mouthparts of a female mosquito feeding on blood. The flexible labium supports the bundle of stylets which penetrates the host's skin. Feeding mosquito, mouthparts labelled.svg
Mouthparts of a female mosquito feeding on blood. The flexible labium supports the bundle of stylets which penetrates the host's skin.

In female mosquitoes, all mouthparts are elongated. The labium encloses all other mouthparts, the stylets, like a sheath. The labrum forms the main feeding tube, through which blood is sucked. The sharp tips of the labrum and maxillae pierce the host's skin. During piercing, the labium remains outside the food item's skin, folding away from the stylets. [9] Saliva containing anticoagulants, is injected into the food item and blood sucked out, each through different tubes.

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.

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 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. [10]

Related Research Articles

<span class="mw-page-title-main">Mosquito</span> Family of flies

Mosquitoes are approximately 3,600 species of small flies comprising the family Culicidae. The word "mosquito" is Spanish for "little fly". Mosquitoes have a slender segmented body, one pair of wings, three pairs of long hair-like legs, and specialized, highly elongated, piercing-sucking mouthparts. Evolutionary biologists view mosquitoes as micropredators, small animals that parasitise larger ones by drinking their blood without immediately killing them. Medical parasitologists view mosquitoes instead as vectors of disease, carrying protozoan parasites or bacterial or viral pathogens from one host to another.

<span class="mw-page-title-main">Fly</span> Order of insects

Flies are insects of the order Diptera, the name being derived from the Greek δι- di- "two", and πτερόν pteron "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced mechanosensory organs known as halteres, which act as high-speed sensors of rotational movement and allow dipterans to perform advanced aerobatics. Diptera is a large order containing an estimated 1,000,000 species including horse-flies, crane flies, hoverflies, mosquitoes and others, although only about 125,000 species have been described.

<span class="mw-page-title-main">Hemiptera</span> Order of insects often called true bugs

Hemiptera is an order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, 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 piercing-sucking mouthparts. The name "true bugs" is often limited to the suborder Heteroptera.

<span class="mw-page-title-main">Pentatomoidea</span> Superfamily of true bugs

The Pentatomoidea are a superfamily of insects in the Heteroptera suborder of the Hemiptera order. As Hemiptera, they share a common arrangement of sucking mouthparts. The roughly 7000 species under Pentatomoidea are divided into 21 families. Among these are the stink bugs and shield bugs, jewel bugs, giant shield bugs, and burrower bugs.

<span class="mw-page-title-main">Haliplidae</span> Family of beetles

The Haliplidae are a family of water beetles that swim using an alternating motion of the legs. They are therefore clumsy in water, and prefer to get around by crawling. The family consists of about 200 species in 5 genera, distributed wherever there is freshwater habitat; it is the only extant member of superfamily Haliploidea. They are also known as crawling water beetles or haliplids.

<span class="mw-page-title-main">Proboscis</span> Elongated mouth part

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.

<span class="mw-page-title-main">Asilidae</span> Family of flies

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 expert predatory habits; they feed mainly or exclusively on other insects and, as a rule, they wait in ambush and catch their prey in flight.

<span class="mw-page-title-main">Nepomorpha</span> Infraorder of true bugs

Nepomorpha is an infraorder of insects in the "true bug" order (Hemiptera). They belong to the "typical" bugs of the suborder Heteroptera. Due to their aquatic habits, these animals are known as true water bugs. They occur all over the world outside the polar regions, with about 2,000 species altogether. The Nepomorpha can be distinguished from related Heteroptera by their missing or vestigial ocelli. Also, as referred to by the obsolete name Cryptocerata, their antennae are reduced, with weak muscles, and usually carried tucked against the head.

<span class="mw-page-title-main">Glossary of entomology terms</span> List of definitions of terms and concepts commonly used in the study of entomology

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

<span class="mw-page-title-main">Mandible (insect mouthpart)</span>

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.

<span class="mw-page-title-main">Arthropod mouthparts</span> Mouthparts of arthropods

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.

<span class="mw-page-title-main">Spider anatomy</span> Physiology of Spiders (order Araneae)

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.

<span class="mw-page-title-main">Mouth</span> First portion of the alimentary canal that receives food

The mouth is the body orifice through which many animals ingest food and vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity, is also the first part of the alimentary canal which leads to the pharynx and the gullet. In tetrapod vertebrates, the mouth is bounded on the outside by the lips and cheeks — thus the oral cavity is also known as the buccal cavity — and contains the tongue on the inside. Except for some groups like birds and lissamphibians, vertebrates usually have teeth in their mouths, although some fish species have pharyngeal teeth instead of oral teeth.

<span class="mw-page-title-main">Mandible (arthropod mouthpart)</span> 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 called 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.

<span class="mw-page-title-main">Maxilla (arthropod mouthpart)</span>

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.

<span class="mw-page-title-main">External morphology of Lepidoptera</span> External features of butterflies and moths

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.

<span class="mw-page-title-main">Insect morphology</span> Description of the physical form of insects

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, three pairs of legs, and mouthparts located outside of the head capsule. This position of the mouthparts divides them from their closest relatives, the non-insect hexapods, which include Protura, Diplura, and Collembola.

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.

<span class="mw-page-title-main">Labellum (insect anatomy)</span>

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

References

  1. Richards, O. W.; Davies, R.G. (1977). Imms' General Textbook of Entomology: Volume 1: Structure, Physiology and Development. Berlin: Springer. ISBN   0-412-61390-5.[ page needed ]
  2. Head, Mandibles, and unusual Labium of Dragonfly Nymph (viewed from below)
  3. Insect Mouthparts
  4. Insect mouthparts - Amateur Entomologists' Society (AES)
  5. "Structure and function of insect mouthparts" (PDF). Archived from the original (PDF) on 2010-06-10. Retrieved 2016-01-08.
  6. "Hymenoptera: ants, bees and wasps", CSIRO, retrieved 8 April 2012
  7. Heppner, John B; Richman, David B; Naranjo, Steven E; Habeck, Dale; Asaro, Christopher; Boevé, Jean-Luc; Baumgärtner, Johann; Schneider, David C; Lambdin, Paris; Cave, Ronald D; Ratcliffe, Brett C; Heppner, John B; Baldwin, Rebecca W; Scherer, Clay W; Frank, J. Howard; Dunford, James C; Somma, Louis A; Richman, David. B; Krafsur, E. S; Crooker, Allen; Heppner, John B; Capinera, John L; Menalled, Fabián D; Liebman, Matt; Capinera, John L; Teal, Peter E. A; Hoy, Marjorie A; Lloyd, James E; Sivinski, John; et al. (2008). "Silkworm Moths (Lepidoptera: Bombycidae)". Encyclopedia of Entomology. pp. 3375–6. doi:10.1007/978-1-4020-6359-6_4198. ISBN   978-1-4020-6242-1.
  8. Walter Reuther (1989). The Citrus Industry: Crop protection, postharvest technology, and early history of citrus research in California. UCANR Publications. pp. 64–. ISBN   978-0-931876-87-5.
  9. Zahran, Nagwan; Sawires, Sameh; Hamza, Ali (2022-10-25). "Piercing and sucking mouth parts sensilla of irradiated mosquito, Culex pipiens (Diptera: Culicidae) with gamma radiation". Scientific Reports. 12 (1): 17833. doi:10.1038/s41598-022-22348-0. PMC   9596698 . PMID   36284127.
  10. Mehlhorn, Heinz (2001). Encyclopedic Reference of Parasitology: Biology, Structure, Function. Springer Science & Business Media. p. 310. ISBN   978-3-540-66819-0.