Dictionary:
a·phid (ā'fĭd, ăf'ĭd)  |
[New Latin Aphis, Aphid-, type genus.]
aphidian a·phid'i·an (ə-fĭd'ē-ən) adj. & n.| 5min Related Video: aphid |
| Britannica Concise Encyclopedia: aphid |
For more information on aphid, visit Britannica.com.
| Sci-Tech Encyclopedia: Aphid |
One of a group of mostly soft-bodied plant-feeding insects of the suborder Homoptera, superfamily Aphidoidea. The worldwide fauna of over 4000 species is most abundant in north temperate regions. Aphids feed on phloem sap from vascular plants, tapping it through a feeding tube formed from modified mandibles and maxillae called stylets. In so doing they may transmit viruses from plant to plant, spreading serious disease in crops such as potatoes, cereals, sugarbeet, and citrus. Plants sometimes react to aphid feeding by forming galls in which the aphids live protected from drought and enemies. The so-called Chinese gall is valued in commerce for its high tannin content.
Aphids have evolved complex life styles to exploit the changing growth phases of plants. Many divide their yearly cycle by flying between a primary host, on which sexual forms mate and lay winter eggs, and a secondary host, where only parthenogenetic females multiply. Only one generation of males and sexual oviparous females occurs each year, usually in autumn. Most parthenogenetic females are also viviparous, and reproduce very rapidly under favorable conditions. Viviparae are winged or wingless (see illustration). Development of young aphids can be switched toward either wingedness or sexuality by outside factors, such as crowding, decreasing temperature, or shortening days. Aphids in the tropics often remain wholly parthenogenetic.
Viviparae of the tulip bulb aphid: (a) the winged form and (b) the wingless form. (After J. Davidson, On some aphids infesting tulips, Bull. Entomol. Res., 18:51–62, 1927)
| Columbia Encyclopedia: aphid |
The life cycle of aphids is complex and varies in different species. In a typical life cycle, several generations of wingless females, which reproduce asexually (see parthenogenesis) and bear live offspring, are followed by a generation of winged females, which bears a sexually reproducing, egg-laying generation of males and females. Mating usually occurs in fall, and the eggs are laid in crevices of the twigs of the host plant; the first generation of wingless females hatches in spring. Different host plants and different parts of the plant may be used at different stages of the life cycle.
Some aphids (e.g., the woolly apple aphid) secrete long strands of waxy material from wax glands, forming a conspicuous woolly coating for their colonies. Gall-making aphids live in galls, or swellings of plant tissue, formed by the plant as a reaction to substances secreted by the insects; galls of different aphid species are easily identified (e.g., the cockscomb gall of elm leaves). One group of aphids lives only on conifers (e.g., the eastern spruce gall aphid).
Ant Cows
Many kinds of aphid secrete a sweet substance called honeydew, prized as food by ants, flies, and bees. This substance consists of partially digested, highly concentrated plant sap and other wastes, and is excreted from the anus, often in copious amounts. Certain aphid species have a symbiotic relationship with various species of ants that resembles the relationship of domestic cattle to humans; hence the name "ant cows" for aphids. The ants tend the aphids, transporting them to their food plants at the appropriate stages of the aphids' life cycle and sheltering the aphid eggs in their nests during the winter. The aphids, in turn, provide honeydew for the ants.
Damage to Plants
The damage done by aphids is due to a number of causes, including loss of sap, clogging of leaf surfaces with honeydew, and growth of molds and fungi on the honeydew. Leaf curl, a common symptom of aphid infestation, occurs when a colony attacks the underside of a leaf, causing its desiccation. The downward curl provides protection for the colony, but the leaf becomes useless to the plant. Some species also transmit viral diseases of plants. Among the aphids causing serious damage to food crops are the grain, cabbage, cornroot, apple, woolly apple, and hickory aphids and the alder and beech tree blights. The phylloxera, notorious for its damage to vineyards, is closely related to the aphids.
Many larger insects that feed on aphids, such as ladybird beetles and lacewings, are used as biological controls of aphid infestations. Fungal infection and damp weather also help limit the number of aphids.
Classification
Aphids are classified in several families of the phylum Arthropoda, class Insecta, order Homoptera.
| Veterinary Dictionary: aphid |
An insect of the order Hemiptera. They parasitize many plants during the warm seasons. Of interest in animal health are the black aphids, Aphis craccivora, which can exist in very large numbers on burr trefoil, Medicago polymorpha, and may stimulate the production of phytoallexins in the plant which then photosensitize animals grazing the infested pasture.
| Gardener's Dictionary: aphid |
A small sucking insect that feeds primarily on new soft growth.
| Wikipedia: Aphid |
| Aphids Fossil range: 280–0 Ma |
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| Aphids feeding on a fennel stalk | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Homoptera |
| Suborder: | Sternorrhyncha |
| Superfamily: | Aphidoidea |
| Families | |
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There are 10 families:
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Aphids, also known as plant lice (and in Britain as greenflies),[1] are small plant-eating insects, and members of the superfamily Aphidoidea.[2] Aphids are among the most destructive insect pests on cultivated plants in temperate regions.[3] The damage they do to plants has made them enemies of farmers and gardeners the world over, but from a purely zoological standpoint they are a very successful group of organisms.[4]
About 4,400 species of 10 families are known. Historically, many fewer families were recognized, as most species were included in the family Aphididae. Around 250 species are serious pests for agriculture and forestry as well as an annoyance for gardeners. They vary in length from one to ten millimetres.
Natural enemies include predatory lady beetles (Coleoptera: Coccinellidae), hoverfly larvae (Diptera: Syrphidae), parasitic wasps, aphid midge larvae, crab spiders[5] lacewings (Neuroptera: Chrysopidae), and entomopathogenic fungi like Lecanicillium lecanii and the Entomophthorales.
Aphids are distributed worldwide, but are most common in temperate zones. Also, in contrast to many taxa, species diversity is much lower in the tropics than in the temperate zones. They can migrate great distances, mainly through passive dispersal by riding on winds. For example, the currant lettuce aphid (Nasonovia ribisnigri Mosley) is believed to have spread from New Zealand to Tasmania in this way.[6] Aphids have also been spread by human transportation of infested plant materials.
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Aphids are in the superfamily Aphidoidea in the homopterous division of the order Hemiptera. Recent classification within Hemiptera has reduced the old taxon "Homoptera" to two suborders: Sternorrhyncha (e.g., aphids, whiteflies, scales, psyllids, etc.) and Auchenorrhyncha (e.g., cicadas, leafhoppers, treehoppers, planthoppers, etc.) with the suborder Hemiptera containing a large group of insects known as the true bugs. More recent reclassifications have substantially rearranged the families within Aphidoidea: some old families were reduced to subfamily rank (e.g., Eriosomatidae), and many old subfamilies elevated to family rank. Taxonomically woolly conifer aphids like the pine aphid, the spruce aphid and the balsam woolly aphid are not true aphids, but adelgids, and lack the cornicles of true aphids.
Aphids, adelgids, and phylloxerids are very closely related, and are either placed in the insect super family Aphidoidea (Blackman and Eastop, 1994) or into two super families (Phylloxeroidea and Aphidoidea) within the order Homoptera, the plant-sucking bugs.[7]
Like aphids, phylloxera feed on the roots, leaves and shoots of grape plants, but unlike aphids do not produce honeydew or cornicle secretions.[8] Phylloxera (Daktulosphaira vitifoliae), are insects which caused the Great French Wine Blight that devastated European viticulture in the 19th century.
Similarly, adelgids also feed on plant phloem. Adelgids are sometimes described as aphids, but more properly as classified as aphid-like insects, because they have no cauda or cornicles.[3]
Most aphids have soft, green bodies, but other colors are common, such as black, brown, and pink. Aphids have antennas with as many as six segments.[3] Aphids feed themselves through sucking mouthparts called stylets, enclosed in a sheath called a rostrum, which is formed from modifications of the mandible and maxilla of the insect mouthparts.[9] They have long, thin legs and two-jointed, two-clawed tarsi.
Most aphids have a pair of cornicles (or "siphunculi"), abdominal tubes through which they exude droplets of a quick-hardening defensive fluid[9] containing triacylglycerols, called cornicle wax. Other defensive compounds can also be produced by some types of aphids.[3]
Aphids have a tail-like protrustion called a "cauda" above their rectal apertures. They have two compound eyes, and an ocular tubercle behind and above each eye, made up of three lenses (called triommatidia).[10][11]
When host plant quality becomes poor or conditions become crowded, some aphid species produce winged offspring, "alates", that can disperse to other food sources. The mouthparts or eyes are smaller or missing in some species and forms.[3]
Many aphid species are monophagous (that is, they feed on only one plant species). Others, like the green peach aphid (Myzus persicae), feed on hundreds of plant species across many families.
Aphids passively feed on sap of phloem vessels in plants, as do many of their fellow members of Hemiptera such as scale insects and cicadas. Once a phloem vessel is punctured, the sap, which is under high pressure, is forced into the aphid's food canal. As they feed, aphids often transmit plant viruses to the plants, such as to potatoes, cereals, sugarbeets and citrus plants.[9] These viruses can sometimes kill the plants.
Plants contain low densities of the nitrogen compounds needed for building proteins. This requires aphids to consume an excess of sap to satisfy their nutritional requirements. The excess is expelled as "honeydew", out of the recta of aphids, in such large volumes that in some instances it can "fall like rain".[3] Aphid honeydew is rich in carbohydrates, like the phloem it derives from.
Some species of ants "farm" aphids, protecting them on the plants they eat, eating the honeydew that the aphids release from the terminations of their alimentary canals. This is a "mutualistic relationship".
These "dairying ants" "milk" the aphids by stroking them with their antennae.[12][13] Therefore, sometimes aphids are called "ant cows".
Some farming ant species gather and store the aphid eggs in their nests over the winter. In the spring, the ants carry the newly-hatched aphids back to the plants. Some species of dairying ants (such as the European yellow meadow ant, Lasius flavus)[14] manage large "herds" of aphids that feed on roots of plants in the ant colony. Queens that are leaving to start a new colony take an aphid egg to found a new herd of underground aphids in the new colony. These farming ants protect the aphids by fighting off aphid predators.[13]
An interesting variation in ant-aphid relationships involves Lycaenid butterflies (such as the Sievers blue butterfly and the Japanese copper butterfly) and the Myrmica ants. For example, Niphanda fusca butterflies lay eggs on plants where ants tend herds of aphids. The eggs hatch as caterpillars which feed on the aphids. The ants do not defend the aphids from the caterpillars, but carry the caterpillars to their nest. In the nest, the ants feed the caterpillars, which produce honeydew for the ants. When the caterpillars reach full size, they crawl to the colony entrance and form cocoons. After two weeks, butterflies emerge and take flight.[15]
Some bees in coniferous forests also collect aphid honeydew to make "forest honey".[9]
Many aphids are host to endosymbiont bacteria, Buchnera, inside specialized cells called bacteriocytes. These bacteria synthesize some essential amino acids that are absent from the phloem that the aphids eat.[16]
Some aphid species have unusual and complex reproductive adaptations, while others have fairly simple reproduction. Adaptations include having both sexual and asexual reproduction, creation of eggs or live nymphs and switches between woody and herbaceous types of host plant at different times of the year.[3][17]
Many aphids undergo cyclical parthenogenesis. In the spring and summer, mostly or only females are present in the population. The overwintering eggs that hatch in the spring result in females, called fundatrices. Reproduction is typically parthenogenetic and viviparous. Females undergo a modified meiosis that results in eggs that are genetically identical to their mother (parthenogenetic). The embryos develop within the mothers' ovarioles, which then give live birth to first instar female nymphs (viviparous). The offspring resemble their parent in every way except size, and are called virginoparae.
This process iterates throughout the summer, producing multiple generations that typically live 20 to 40 days. Thus one female hatched in spring may produce many billions of descendants. For example, some species of cabbage aphids (like Brevicoryne brassicae) can produce up to 41 generations of females.
In autumn, aphids undergo sexual, oviparous reproduction. A change in photoperiod and temperature, or perhaps a lower food quantity or quality, causes females to parthenogenetically produce sexual females and males. The males are genetically identical to their mothers except that they have one less sex chromosome. These sexual aphids may lack wings or even mouthparts.[3] Sexual females and males mate, and females lay eggs that develop outside the mother. The eggs endure the winter and emerge as winged or wingless females the following spring. This is, for example, the life cycle of the rose aphid (Aphis rosae), which may be considered typical of the family. However in warm environments, such as in the tropics or in a greenhouse, aphids may go on reproducing asexually for many years.[9]
Some species produce winged females in the summer, sometimes in response to low food quality or quantity. The winged females migrate to start new colonies on a new plant, often of quite a different kind. For example, the apple aphid (Aphis mali), after producing many generations of wingless females on its typical food-plant, gives rise to winged forms which fly away and settle on grass or corn-stalks.
Some aphids have telescoping generations. That is, the parthenogenetic, viviparous female has a daughter within her, who is already parthenogenetically producing her own daughter. Thus a female's diet can affect the body size and birth rate of more than two generations (daughters and granddaughters).[18][19]
Aphids probably appeared around 280 million years ago, in the early Permian period. They probably fed on plants like Cordaitales or Cycadophyta. The oldest known aphid fossil is of the species Triassoaphis cubitus Evans from the Triassic.[20] The number of species was small, but increased considerably with the appearance of angiosperms 160 million years ago. Angiosperms allowed aphids to specialize. Organs like the cornicles did not appear until the Cretaceous period.
Aphids are soft-bodied, and have a wide variety of insect predators. Aphids also are often infected by bacteria, viruses and fungi. Aphids are affected by the weather, such as precipitation,[21] temperature[22] and wind.[23]
Insects that attack aphids include predatory lady bugs (Coleoptera: Coccinellidae) (ladybirds in the UK), hoverfly larvae (Diptera: Syrphidae), parasitic wasps, aphid midge larvae, aphid lions, crab spiders[5] and lacewings (Neuroptera: Chrysopidae).
Fungi that attack aphids include Neozygites fresenii, Entomophthora, Beauveria bassiana, Metarhizium anisopliae and entomopathogenic fungi like Lecanicillium lecanii. Aphids brush against the microscopic spores. These spores stick to the aphid, germinate and penetrate the aphid's skin. The fungus grows in the aphid hemolymph (i.e., the counterpart of blood for aphids). After about 3 days, the aphid dies and the fungus releases more spores into the air. Infected aphids are covered with a woolly mass that progressively grows thicker until the aphid is obscured. Often the visible fungus is not the type of fungus that killed the aphid, but a secondary fungus.[21]
Aphids can be easily killed by unfavorable weather, such as late spring freezes.[24] Excessive heat kills the symbiotic bacteria that some aphids depend on, which makes the aphids infertile.[25] Rain prevents winged aphids from dispersing, and knocks aphids off plants and thus kills them from the impact or by starvation.[21][26][27] However, Ken Ostlie, an entomologist with the University of Minnesota Extension Service, suggests that rain should not be relied on for aphid control.[28]
Aphids are soft-bodied, and have little protection from predators and diseases. Some species of aphid interact with plant tissues forming a gall, an abnormal swelling of plant tissue. Aphids can live inside the gall, which provides protection from predators and the elements. A number of galling aphid species are known to produce specialised "soldier" forms, sterile nymphs with defensive features which defend the gall from invasion.[30][9] For example, Alexander's horned aphids are a type of soldier aphid that has a hard exoskeleton and pincer-like mouthparts.[31] Infestation of a variety of Chinese trees by Chinese sumac aphids (Melaphis chinensis Bell) can create a "Chinese gall" which is valued as a commercial product. As "Galla Chinensis", Chinese galls are used in Chinese medicine to treat coughs, diarrhea, night sweats, dysentry and to stop intestinal and uterine bleeding. Chinese galls are also an important source of tannins.[9]
Some species of aphid, known as "woolly aphids" (Eriosomatinae), excrete a "fluffy wax coating" for protection.[9]
The cabbage aphid (Brevicoryne brassicae) stores and releases chemicals that produce a violent chemical reaction and strong mustard oil smell to repel predators.
It was common at one time to suggest that the cornicles were the source of the honeydew, and this was even included in the Shorter Oxford English Dictionary[32] and the 2008 edition of the World Book Encyclopedia.[33]. In fact, honeydew secretions are produced from the anus of the aphid[34], while cornicles mostly produce defensive chemicals such as waxes. There also is evidence of cornicle wax attracting aphid predators in some cases.[35] Aphids are also known to defend themselves from attack by parasitoid wasps by kicking.
Plants exhibiting aphid damage can have a variety of symptoms, such as decreased growth rates, mottled leaves, yellowing, stunted growth, curled leaves, browning, wilting, low yields and death. The removal of sap creates a lack of vigour in the plant, and aphid saliva is toxic to plants. Aphids frequently transmit disease-causing organisms like plant viruses to their hosts. The green peach aphid (Myzus persicae) is a vector for more than 110 plant viruses. Cotton aphids (Aphis gossypii) often infect sugarcane, papaya and groundnuts with viruses.[3] Aphids contributed to the spread of late blight (Phytophthora infestans) among potatoes in the Great Irish Potato Famine of the 1840s.[36]
The cherry aphid or black cherry aphid, Myzus cerasi, is responsible for some leaf curl of cherry trees. This can easily be distinguished from 'leaf curl' caused by Taphrina fungus species due to the presence of aphids beneath the leaves.
The coating of plants with honeydew can contribute to the spread of fungi which can damage plants.[37][38][39] Honeydew produced by aphids has been observed to reduce the effectiveness of fungicides as well.[40]
A hypothesis that insect feeding may improve plant fitness was floated in the mid-1970s by Owen and Wiegert. It was felt that the excess honeydew would nourish soil micro-organisms, including nitrogen fixers. In a nitrogen poor environment, this could provide an advantage to an infested plant over a noninfested plant. However, this does not appear to be supported by the observational evidence.[41]
The damage of plants, and in particular commercial crops, has resulted in large amounts of resources and efforts being spent attempting to control the activities of aphids.[3]
There are various chemicals that can be used for controlling aphids. Nowadays, there are many plant extracts and plant products that are eco-friendly and are more effective control of aphids. A recent findings of Shreth et. al. suggested use of Neem products and Lantana products to protect plants against aphids.[42]
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| Translations: Aphid |
Français (French)
n. - puceron, aphidien
Deutsch (German)
n. - Blattlaus
Ελληνική (Greek)
n. - αφίδα, μελίγκρα, φυτοψείρα
Português (Portuguese)
n. - afídeo (m) (Zool.), pulgão (m) (Zool.)
Русский (Russian)
тля растительная
Español (Spanish)
n. - áfido, pulgón, piojillo
Svenska (Swedish)
n. - bladlus
中文（简体）(Chinese (Simplified))
蚜虫
中文（繁體）(Chinese (Traditional))
n. - 蚜蟲
العربيه (Arabic)
(الاسم) أرقه , المن : حشره تمتص عصارة النبات
עברית (Hebrew)
n. - כנימה (חרק קטן)
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
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| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/. Read more |
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| Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
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| Gardener's Dictionary. Taylor's Dictionary for Gardeners, by Frances Tenenbaum. Copyright © 1997 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Aphid". Read more |
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