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Aphids are small
sap SAP SE () is a German multinational software corporation based in Walldorf, Baden-Württemberg Baden-Württemberg (; ) is a States of Germany, state (''Land'') in southwest Germany, east of the Rhine, which forms the southern part of Ge ...

sap
-sucking
insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

insect
s and members of the
superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...
Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A typical life cycle involves flightless females giving living birth to female
nymphs A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the dialects of the Gree ...
—who may also be already pregnant, an adaptation scientists call telescopic development—without the involvement of males. Maturing rapidly, females breed profusely so that the number of these insects multiplies quickly. Winged females may develop later in the season, allowing the insects to colonize new plants. In temperate regions, a phase of sexual reproduction occurs in the autumn, with the insects often overwintering as eggs. The life cycle of some species involves an alternation between two species of host plants, for example between an annual crop and a woody plant. Some species feed on only one type of plant, while others are generalists, colonizing many plant groups. About 5,000 species of aphid have been described, all included in the family
Aphididae The Aphididae are a very large insect family (biology), family in the aphid Taxonomic rank, superfamily (Aphidoidea), of the order (biology), order Hemiptera. Several thousand species are placed in this family (biology), family, many of which are ...

Aphididae
. Around 400 of these are found on food and fiber crops, and many are serious pests of
agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors su ...

agriculture
and
forestry Forestry is the science and craft of creating, managing, planting, using, conserving and repairing forest A forest is an area of land dominated by tree In botany, a tree is a perennial plant with an elongated Plant stem, ste ...
, as well as an annoyance for
gardener A gardener is someone who practices gardening Gardening is the practice of growing and cultivating plants as part of horticulture Horticulture is the art of cultivating plants in gardens to produce food and medicinal ingredients, or for comfor ...

gardener
s. So-called dairying
ant Ants are eusocial Eusociality (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...

ant
s have a mutualistic relationship with aphids, tending them for their honeydew, and protecting them from
predator Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical env ...

predator
s. Aphids are among the most destructive insect pests on cultivated plants in temperate regions. In addition to weakening the plant by sucking sap, they act as
vectors Vector may refer to: Biology *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism; a disease vector *Vector (molecular biology), a DNA molecule used as a vehicle to artificially carr ...
for
plant virus Plant viruses are virus A virus is a submicroscopic infectious agent In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processe ...

plant virus
es and disfigure ornamental plants with deposits of honeydew and the subsequent growth of
sooty mould 350px, Sooty mold caused by scale on a ''Eucalyptus dives'' Sooty mold is a collective term for different Ascomycete fungi, which includes many genera, commonly ''Cladosporium'' and ''Alternaria''. It grows on plants and their fruit, but also envi ...
s. Because of their ability to rapidly increase in numbers by
asexual reproduction Asexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism In biology, an organism (from Ancient Gree ...
and telescopic development, they are a highly successful group of organisms from an ecological standpoint. Control of aphids is not easy. Insecticides do not always produce reliable results, given resistance to several classes of insecticide and the fact that aphids often feed on the undersides of leaves. On a garden scale, water jets and soap sprays are quite effective. Natural enemies include predatory
ladybugs
ladybugs
,
hoverfly Hover flies, also called flower flies or syrphid flies, make up the insect family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is ...

hoverfly
larvae,
parasitic wasp Parasitoid wasps are a large group of hymenoptera Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition ...

parasitic wasp
s, aphid midge larvae,
crab spider The Thomisidae are a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain ...

crab spider
s,
lacewing The insect Insects or Insecta (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Thr ...

lacewing
larvae, and
entomopathogenic fungi An entomopathogenic fungus is a fungus that can act as a parasite of insects and kills or seriously disables them. s killed by the entomopathogenic fungus ''Beauveria bassiana'' ( Ascomycota: Hypocreales) Typical life cycle Image:Pandora neoap ...
. An
integrated pest management Integrated pest management (IPM), also known as integrated pest control (IPC) is a broad-based approach that integrates practices for economic . IPM aims to suppress pest populations below the economic injury level (EIL). The UN's defines IPM as ...
strategy using
biological pest control Biological control or biocontrol is a method of controlling pests such as insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was ...
can work, but is difficult to achieve except in enclosed environments such as glasshouses.


Distribution

Aphids are distributed worldwide, but are most common in
temperate zone In geography, the temperate climates of Earth occur in the middle latitudes (40° to 60° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout the yea ...

temperate zone
s. In contrast to many
taxa In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
, aphid species diversity is much lower in the tropics than in the temperate zones. They can migrate great distances, mainly through passive dispersal by winds. Winged aphids may also rise up in the day as high as 600 m where they are transported by strong winds. For example, the currant-lettuce aphid, ''
Nasonovia ribisnigri ''Nasonovia ribisnigri'' is a species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...

Nasonovia ribisnigri
'', is believed to have spread from
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
to
Tasmania Tasmania (), abbreviated as TAS, is an island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atol ...
around 2004 through easterly winds. Aphids have also been spread by human transportation of infested plant materials, making some species nearly
cosmopolitan Cosmopolitan may refer to: Food and drink * Cosmopolitan (cocktail), also known as a "Cosmo" History * Rootless cosmopolitan, a Soviet derogatory epithet during Joseph Stalin's anti-Semitic campaign of 1949–1953 Hotels and resorts * Cosmopo ...
in their distribution.


Evolution


Fossil history

Aphids, and the closely related adelgids and phylloxerans, probably evolved from a common ancestor some , in the
Early Permian#REDIRECT One (disambiguation) One or 1 is the first natural number. 1, one, or ONE may also refer to: * AD 1, first year of the AD era * 1 BC, the year before AD 1 * One (pronoun), ''One'' (pronoun), a pronoun in the English language * Hydrogen, ...
period. They probably fed on plants like
Cordaitales Cordaitales are an extinct order of woody plants that may have been early conifer Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyt ...
or
Cycadophyta :''For the insect, see Cicada.'' Cycads are seed plants with a very long fossil history that were formerly more abundant and more diverse than they are today. They typically have a stout and woody ( ligneous) trunk with a crown of large, ha ...

Cycadophyta
. With their soft bodies, aphids do not fossilize well, and the oldest known
fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication used by humans, inc ...

fossil
is of the species '' Triassoaphis cubitus'' from the
Triassic The Triassic ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth ...

Triassic
. They do however sometimes get stuck in plant exudates which solidify into
amber Amber is fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was ...

amber
. In 1967, when Professor Ole Heie wrote his monograph ''Studies on Fossil Aphids'', about sixty species have been described from the Triassic,
Jurassic The Jurassic ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth ...
,
Cretaceous The Cretaceous ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of division ...

Cretaceous
and mostly the
Tertiary Tertiary ( ) is a widely used but obsolete term for the Period (geology), geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-bird, avian dinosaurs in the Cretaceous–Paleogene extincti ...

Tertiary
periods, with
Baltic amber , Poland. The Baltic region is home to the largest known deposit of amber, called Baltic amber or succinite. It dates from 44 million years ago (during the Eocene epoch). It has been estimated that these forests created more than 100,000 tons of ...

Baltic amber
contributing another forty species. The total number of species was small, but increased considerably with the appearance of the
angiosperm Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ...

angiosperm
s , as this allowed aphids to specialise, the speciation of aphids going hand-in-hand with the diversification of flowering plants. The earliest aphids were probably
polyphagous Feeding is the process by which organisms, typically animals, obtain food. Terminology often uses either the suffixes -vore, -vory, or -vorous from Latin ''vorare'', meaning "to devour", or -phage, -phagy, or -phagous from Greek φαγε ...
, with
monophagy Feeding is the process by which organisms, typically animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotr ...
developing later. It has been hypothesized that the ancestors of the
Adelgidae The Adelgidae are a small family of the Hemiptera closely related to the aphids, and often included in the Aphidoidea with the Phylloxeridae or placed within the superfamily Phylloxeroidea as a sister of the Aphidoidea within the infraorder Ap ...
lived on
conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ex ...
s while those of the Aphididae fed on the sap of
Podocarpaceae Podocarpaceae is a large family of mainly Southern Hemisphere conifers, comprising about 156 species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a un ...
or
Araucariaceae Araucariaceae – also known as araucarians – is a very ancient family of conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinop ...
that survived extinctions in the late Cretaceous. Organs like the cornicles did not appear until the Cretaceous period. One study alternatively suggests that ancestral aphids may have lived on angiosperm bark and that feeding on leaves may be a
derived trait 279px, trait Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for structuring object-oriented programs (a template class in the C++ programming languag ...
. The Lachninae have long mouth parts that are suitable for living on bark and it has been suggested that the mid-Cretaceous ancestor fed on the bark of angiosperm trees, switching to leaves of conifer hosts in the late Cretaceous. The Phylloxeridae may well be the oldest family still extant, but their fossil record is limited to the
Lower Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene The Miocene ( ) is the first Epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish author Charles Lyell ...
'' Palaeophylloxera''.


Taxonomy

Late 20th-century reclassification within the Hemiptera reduced the old taxon "Homoptera" to two suborders:
Sternorrhyncha The Sternorrhyncha suborder of the Hemiptera contains the aphids, whiteflies, and scale insects, groups which were traditionally included in the order Homoptera. "Sternorrhyncha" refers to the rearward position of the mouthparts relative to the ...
(aphids, whiteflies,
scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory)In the mathematical discipline of descriptive set theory, a scale is a certain kind of object defined on a set (mathematics), set of point (mathematics), points in some Poli ...

scales
,
psyllids Psyllidae, the jumping plant lice or psyllids, are a Family (biology), family of small plant-feeding insects that tend to be very host-specific, i.e. each plant-louse species only feeds on one plant species (monophagous) or feeds on a few closely ...
, etc.) and
Auchenorrhyncha The Auchenorrhyncha (former synonym: Cicadinea) suborder of the Hemiptera contains most of the familiar members of what was called the Homoptera – groups such as cicadas, leafhoppers, treehoppers, planthoppers, and spittlebugs. The aphids and sc ...

Auchenorrhyncha
(
cicada The cicadas () are a superfamily, the Cicadoidea, of insect Insects (from Latin ') are pancrustacean Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects ha ...

cicada
s,
leafhopper A leafhopper is the common name for any species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the la ...

leafhopper
s,
treehopper Treehoppers (more precisely typical treehoppers to distinguish them from the Aetalionidae) and thorn bugs are members of the family In human society, family (from la, familia) is a group of people related either by consanguinity (by rec ...

treehopper
s,
planthopper A planthopper is any insect in the infraorder Fulgoromorpha, in the suborder Auchenorrhyncha, and exceeding 12,500 described species worldwide. The name comes from their remarkable resemblance to leaves and other plants of their environment and ...

planthopper
s, etc.) with the suborder
Heteroptera The Heteroptera are a group of about 40,000 species of insects in the order Hemiptera. They are sometimes called "true bugs", though that name more commonly refers to the Hemiptera as a whole. "Typical bugs" might be used as a more unequivocal alt ...

Heteroptera
containing a large group of insects known as the
true bugs Hemiptera (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Re ...
. The infraorder Aphidomorpha within the Sternorrhyncha varies with circumscription with several fossil groups being especially difficult to place but includes the Adelgoidea, the Aphidoidea and the Phylloxeroidea. Some authors use a single superfamily Aphidoidea within which the
Phylloxeridae Phylloxeridae is a small family of plant-parasitic hemipterans closely related to Aphidoidea, aphids with only 75 described species. This group comprises two Subfamily, subfamilies (Phylloxerininae and Phylloxerinae) and 11 Genus, genera with o ...
and Adelgidae are also included while others have Aphidoidea with a sister superfamily Phylloxeroidea within which the Adelgidae and Phylloxeridae are placed. Early 21st-century reclassifications substantially rearranged the families within Aphidoidea: some old families were reduced to subfamily rank (''e.g.'', Eriosomatidae), and many old subfamilies were elevated to family rank. The most recent authoritative classifications have three superfamilies Adelgoidea, Phylloxeroidea and Aphidoidea. The Aphidoidea includes a single large family
Aphididae The Aphididae are a very large insect family (biology), family in the aphid Taxonomic rank, superfamily (Aphidoidea), of the order (biology), order Hemiptera. Several thousand species are placed in this family (biology), family, many of which are ...

Aphididae
that includes all the ~5000 extant species.


Phylogeny


External

Aphids, adelgids, and are very closely related, and are all within the suborder Sternorrhyncha, the plant-sucking bugs. They are either placed in the insect superfamily Aphidoidea or into the superfamily
Phylloxeroidea The PhylloxeroideaHerrich-Schaeffer (1854) In Koch. ''Vorwort des Herausgebers. Die Pflanzenläuse Aphiden getreu nach dem Leben abgebildet und beschrieben, Verlag von J. L. Lotzbeck, Nürnberg'' 1:III-VIII is a small superfamily of the Hemiptera ...
which contains the family Adelgidae and the family Phylloxeridae. Like aphids, phylloxera feed on the roots, leaves, and shoots of grape plants, but unlike aphids, do not produce honeydew or
cornicle The cornicle (or siphuncule) is one of a pair of small upright backward-pointing tubes found on the dorsal side of the 5th or 6th abdominal segments of aphids Aphids are small sap-sucking insects and members of the Taxonomic rank, superfamily ...
secretions. Phylloxera (''Daktulosphaira vitifoliae'') are insects which caused the
Great French Wine Blight The Great French Wine Blight was a severe blight of the mid-19th century that destroyed many of the vineyards in France and laid waste the wine industry. It was caused by an aphid (the actual genus of the aphid is still debated, although it is larg ...
that devastated European
viticulture Viticulture (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power o ...

viticulture
in the 19th century. Similarly, adelgids or woolly conifer aphids, also feed on plant phloem and are sometimes described as aphids, but are more properly classified as aphid-like insects, because they have no cauda or cornicles. The treatment of the groups especially concerning fossil groups varies greatly due to difficulties in resolving relationships. Most modern treatments include the three superfamilies, the Adelogidea, the Aphidoidea, and the Phylloxeroidea within the infraorder Aphidomorpha along with several fossil groups but other treatments have the Aphidomorpha containing the Aphidoidea with the families Aphididae, Phylloxeridae and Adelgidae; or the Aphidomorpha with two superfamilies, Aphidoidea and Phylloxeroidea, the latter containing the Phylloxeridae and the Adelgidae. The
phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree (graph theory), tree showing the evolutionary relationships among va ...

phylogenetic tree
of the Sternorrhyncha is inferred from analysis of small subunit (18S)
ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consis ...
.


Internal

The phylogenetic tree, based on Papasotiropoulos 2013 and Kim 2011, with additions from Ortiz-Rivas and Martinez-Torres 2009, shows the internal
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree (graph theory), tree showing the evolutionary relationships among va ...

phylogeny
of the Aphididae. It has been suggested that the phylogeny of the aphid groups might be revealed by examining the phylogeny of their bacterial
endosymbiont An endosymbiont or endobiont is any organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mol ...
s, especially the obligate endosymbiont '' Buchnera''. The results depend on the assumption that the symbionts are strictly transmitted vertically through the generations. This assumption is well supported by the evidence, and several phylogenetic relationships have been suggested on the basis of endosymbiont studies.


Anatomy

Most aphids have soft bodies, which may be green, black, brown, pink, or almost colorless. Aphids have antennae with two short, broad basal segments and up to four slender terminal segments. They have a pair of
compound eye as imaged by an electron microscope A compound eye is a Eye, visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidium, ommatidia, which are tiny independent photoreception units that consist of ...

compound eye
s, with an ocular tubercle behind and above each eye, made up of three lenses (called triommatidia). They feed on sap using sucking mouthparts called stylets, enclosed in a sheath called a rostrum, which is formed from modifications of the
mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...
and
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The tw ...
of the insect mouthparts. They have long, thin legs with two-jointed, two-clawed tarsi. The majority of aphids are wingless, but winged forms are produced at certain times of year in many species. Most aphids have a pair of cornicles (siphunculi), abdominal tubes on the dorsal surface of their fifth abdominal segment, through which they exude droplets of a quick-hardening defensive fluid containing
triacylglycerol 300px, Example of an unsaturated fat triglyceride (C55H98O6). Left part: glycerol; right part, from top to bottom: palmitic acid, oleic acid">palmitic_acid.html" ;"title="glycerol; right part, from top to bottom: palmitic acid">glycerol; right par ...
s, called cornicle wax. Other defensive compounds can also be produced by some species. Aphids have a tail-like protrusion called a cauda above their rectal apertures. When host plant quality becomes poor or conditions become crowded, some aphid species produce winged offspring (
alateAlate (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, i ...
s) that can disperse to other food sources. The mouthparts or eyes can be small or missing in some species and forms.


Diet

Many aphid species are monophagous (that is, they feed on only one plant species). Others, like the green peach aphid, feed on hundreds of plant species across many
families In human society, family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of families is to maintain the w ...
. About 10% of species feed on different plants at different times of the year. A new host plant is chosen by a winged adult by using visual cues, followed by olfaction using the antennae; if the plant smells right, the next action is probing the surface upon landing. The stylus is inserted and saliva secreted, the sap is sampled, the xylem may be tasted and finally, the phloem is tested. Aphid saliva may inhibit phloem-sealing mechanisms and has pectinases that ease penetration. Non-host plants can be rejected at any stage of the probe, but the transfer of viruses occurs early in the investigation process, at the time of the introduction of the saliva, so non-host plants can become infected. Aphids usually feed passively on
sap SAP SE () is a German multinational software corporation based in Walldorf, Baden-Württemberg Baden-Württemberg (; ) is a States of Germany, state (''Land'') in southwest Germany, east of the Rhine, which forms the southern part of Ge ...

sap
of
phloem Phloem (, ) is the living tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa ...

phloem
vessels in plants, as do many of other hemipterans such as scale insects and cicadas. Once a phloem vessel is punctured, the sap, which is under pressure, is forced into the aphid's food canal. Occasionally, aphids also ingest
xylem Xylem is one of the two types of transport tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North Ame ...

xylem
sap, which is a more dilute diet than phloem sap as the concentrations of sugars and amino acids are 1% of those in the phloem. Xylem sap is under negative hydrostatic pressure and requires active sucking, suggesting an important role in aphid physiology. As xylem sap ingestion has been observed following a dehydration period, aphids are thought to consume xylem sap to replenish their water balance; the consumption of the dilute sap of xylem permitting aphids to rehydrate. However, recent data showed aphids consume more xylem sap than expected and they notably do so when they are not dehydrated and when their fecundity decreases. This suggests aphids, and potentially, all the phloem-sap feeding species of the order Hemiptera, consume xylem sap for reasons other than replenishing water balance. Although aphids passively take in phloem sap, which is under pressure, they can also draw fluid at negative or atmospheric pressure using the cibarial-pharyngeal pump mechanism present in their head. Xylem sap consumption may be related to
osmoregulation Osmoregulation is the active regulation of the osmotic pressure of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, ...
. High osmotic pressure in the stomach, caused by high sucrose concentration, can lead to water transfer from the hemolymph to the stomach, thus resulting in hyperosmotic stress and eventually to the death of the insect. Aphids avoid this fate by osmoregulating through several processes. Sucrose concentration is directly reduced by assimilating sucrose toward metabolism and by synthesizing
oligosaccharide An oligosaccharide (/ˌɑlɪgoʊˈsækəˌɹaɪd/; from the Greek ὀλίγος ''olígos'', "a few", and σάκχαρ ''sácchar'', "sugar") is a saccharide is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sug ...
s from several sucrose
molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...

molecule
s, thus reducing the solute concentration and consequently the osmotic pressure. Oligosaccharides are then excreted through honeydew, explaining its high sugar concentrations, which can then be used by other animals such as ants. Furthermore, water is transferred from the
hindgut The hindgut (or epigaster) is the Posterior (anatomy), posterior (Caudal (anatomical term), caudal) part of the alimentary canal. In mammals, it includes the Anatomical terms of location#Proximal and distal, distal third of the transverse colon and ...
, where osmotic pressure has already been reduced, to the stomach to dilute stomach content. Eventually, aphids consume xylem sap to dilute the stomach osmotic pressure. All these processes function synergetically, and enable aphids to feed on high-sucrose-concentration plant sap, as well as to adapt to varying sucrose concentrations. Plant sap is an unbalanced diet for aphids, as it lacks
essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life forms ...
s, which aphids, like all animals, cannot synthesise, and possesses a high
osmotic pressure Osmotic pressure is the minimum pressure Pressure (symbol: ''p'' or ''P'') is the force In physics, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with ...

osmotic pressure
due to its high
sucrose Sucrose is a type of sugar Sugar is the generic name for , soluble s, many of which are used in food. Simple sugars, also called s, include , , and . Compound sugars, also called s or double sugars, are molecules made of two monosacchari ...

sucrose
concentration. Essential amino acids are provided to aphids by bacterial
endosymbionts An endosymbiont or endobiont is any organism that lives within the body or cells of another organism most often, though not always, in a mutualism (biology), mutualistic relationship. (The term endosymbiosis is from the Greek language, Greek: ἔ ...

endosymbionts
, harboured in special cells,
bacteriocyte A bacteriocyte (Greek language, Greek for ''bacteria cell''), also known as a mycetocyte, is a specialized adipocyte found primarily in certain insect groups such as aphids, tsetse flies, German cockroaches, weevils. These cells contain Endosymbios ...
s. These symbionts recycle glutamate, a metabolic waste of their host, into essential amino acids.


Carotenoids and photoheterotrophy

Some species of aphids have acquired the ability to synthesise red
carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organ ...
s by
horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient G ...
from
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
. They are the only animals other than two-spotted spider mites and the
oriental hornet The Oriental hornet (''Vespa orientalis'') is a social insect of the family Vespidae. It can be found in Southwest Asia, Northeast Africa, the island of Madagascar (but no reports have been made of its presence on the island for many years), the ...

oriental hornet
with this capability. Using their carotenoids, aphids may well be able to absorb solar energy and convert it to a form that their cells can use,
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
. This is the only known example of
photoheterotrophPhotoheterotrophs ('' Gk'': ''photo'' = light, ''hetero'' = (an)other, ''troph'' = nourishment) are heterotrophic phototrophs – that is, they are organisms that use light for energy, but cannot use carbon dioxide Carbon dioxide (chemical form ...
y in animals. The
carotene The term carotene (also carotin, from the Latin ''carota'', "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the exce ...

carotene
pigments in aphids form a layer close to the surface of the cuticle, ideally placed to absorb sunlight. The excited carotenoids seem to reduce NAD to
NADH Nicotinamide adenine dinucleotide (NAD) is a Cofactor (biochemistry), coenzyme central to metabolism. Found in all living cell (biology), cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate ...
which is oxidized in the
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
for energy.


Reproduction

The simplest reproductive strategy is for an aphid to have a single host all year round. On this it may alternate between sexual and asexual generations (holocyclic) or alternatively, all young may be produced by
parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction Asexual reproduction is a typ ...
,
egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excluding s), and lay eggs, although some, such as s, do not. eg ...

egg
s never being laid (anholocyclic). Some species can have both holocyclic and anholocyclic populations under different circumstances but no known aphid species reproduce solely by sexual means. The alternation of sexual and asexual generations may have evolved repeatedly. However, aphid reproduction is often more complex than this and involves migration between different host plants. In about 10% of species, there is an alternation between woody (primary hosts) on which the aphids overwinter and
herbaceous Herbaceous plants are vascular plants that have no persistent wood, woody stems above ground, including many perennial plant, perennials, and nearly all Annual plant, annuals and Biennial plant, biennials. Definitions of "herb" and "herbaceous" ...
(secondary) host plants, where they reproduce abundantly in the summer. A few species can produce a soldier caste, other species show extensive
polyphenism A polyphenic trait is a trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions. It is therefore a special case of phenotypic plasticity. There are several types of polyph ...
under different environmental conditions and some can control the sex ratio of their offspring depending on external factors. When a typical sophisticated reproductive strategy is used, only females are present in the population at the beginning of the seasonal cycle (although a few species of aphids have been found to have both male and female sexes at this time). The overwintering eggs that hatch in the spring result in females, called fundatrices (stem mothers). Reproduction typically does not involve males (
parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction Asexual reproduction is a typ ...
) and results in a live birth (
viviparity Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the mo ...
). The live young are produced by pseudoplacental viviparity, which is the development of eggs, deficient in the yolk, the embryos fed by a tissue acting as a placenta. The young emerge from the mother soon after hatching. Eggs are parthenogenetically produced without
meiosis Meiosis (; , because it is a reductional division) is a special type of of in organisms used to produce the , such as or . It involves two rounds of division that ultimately result in four cells with only one copy of each (). Additionall ...

meiosis
and the offspring are clonal to their mother, so they are all female (
thelytoky Thelytoky (from the Greek ''thēlys'' "female" and ''tokos'' "birth") is a type of parthenogenesis in which females are produced from unfertilized eggs, as for example in aphids. Thelytokous parthenogenesis is rare among animals and reported in ...
). The embryos develop within the mothers' ovarioles, which then give birth to live (already hatched) first-
instar An instar (, from the Latin ''īnstar'', "form", "likeness") is a developmental stage of arthropods An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly ...
female nymphs. As the eggs begin to develop immediately after ovulation, an adult female can house developing female nymphs which already have parthenogenetically developing embryos inside them (i.e. they are born pregnant). This telescoping of generations enables aphids to increase in number with great rapidity. The offspring resemble their parent in every way except size. Thus, a female's diet can affect the body size and birth rate of more than two generations (daughters and granddaughters). This process repeats itself throughout the summer, producing multiple generations that typically live 20 to 40 days. For example, some species of cabbage aphids (like '' Brevicoryne brassicae'') can produce up to 41 generations of females in a season. Thus, one female hatched in spring can theoretically produce billions of descendants, were they all to survive. In autumn, aphids reproduce sexually and lay eggs. Environmental factors such as a change in
photoperiodPhotoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark ...
and
temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concept ...

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, with the aphids'
X0 sex-determination system The X0 sex-determination system determines the sex of offspring among: * Most arachnidsBull, James J.; ''Evolution of sex determining mechanisms''; p. 17 with the exception of mites where a small majority are haplodiploid, * Almost all Apterygota, ...
, they have one fewer
sex chromosome A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical p ...
. These sexual aphids may lack wings or even mouthparts. Sexual females and males mate, and females lay eggs that develop outside the mother. The eggs survive the winter and hatch into winged (alate) or wingless females the following spring. This occurs in, for example, the
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring *Life-cycle hypothesis, ...
of the rose aphid (''Macrosiphum rosae''), which may be considered typical of the family. However, in warm environments, such as in the tropics or a greenhouse, aphids may go on reproducing asexually for many years. Aphids reproducing asexually by
parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction Asexual reproduction is a typ ...
can have genetically identical winged and non-winged female progeny. Control is complex; some aphids alternate during their life-cycles between genetic control (Polymorphism (biology), polymorphism) and environmental control (
polyphenism A polyphenic trait is a trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions. It is therefore a special case of phenotypic plasticity. There are several types of polyph ...
) of production of winged or wingless forms. Winged progeny tend to be produced more abundantly under unfavorable or stressful conditions. Some species produce winged progeny in response to low food quality or quantity. e.g. when a host plant is starting to senesce. The winged females migrate to start new colonies on a new host plant. For example, the apple aphid (''Aphis pomi''), after producing many generations of wingless females gives rise to winged forms that fly to other branches or trees of its typical food plant. Aphids that are attacked by , Neuroptera, lacewings, parasitoid wasps, or other predators can change the dynamics of their progeny production. When aphids are attacked by these predators, alarm pheromones, in particular Farnesene, beta-farnesene, are released from the
cornicle The cornicle (or siphuncule) is one of a pair of small upright backward-pointing tubes found on the dorsal side of the 5th or 6th abdominal segments of aphids Aphids are small sap-sucking insects and members of the Taxonomic rank, superfamily ...
s. These alarm pheromones cause several behavioral modifications that, depending on the aphid species, can include walking away and dropping off the host plant. Additionally, alarm pheromone perception can induce the aphids to produce winged progeny that can leave the host plant in search of a safer feeding site. Viral infections, which can be extremely harmful to aphids, can also lead to the production of winged offspring. For example, ''Ambidensovirus, Densovirus'' infection has a negative impact on rosy apple aphid (
Dysaphis plantaginea
') reproduction, but contributes to the development of aphids with wings, which can transmit the virus more easily to new host plants. Additionally, symbiotic bacteria that live inside of the aphids can also alter aphid reproductive strategies based on the exposure to environmental stressors. In the autumn, host-alternating (heteroecious) aphid species produce a special winged generation that flies to different host plants for the sexual part of the life cycle. Flightless female and male sexual forms are produced and lay eggs. Some species such as ''Aphis fabae'' (black bean aphid), ''Metopolophium dirhodum'' (rose-grain aphid), ''Myzus persicae'' (peach-potato aphid), and ''Rhopalosiphum padi'' (bird cherry-oat aphid) are serious pests. They overwinter on primary hosts on trees or bushes; in summer, they migrate to their secondary host on a herbaceous plant, often a crop, then the gynoparae return to the tree in autumn. Another example is the soybean aphid (''Aphis glycines''). As fall approaches, the soybean plants begin to senesce from the bottom upwards. The aphids are forced upwards and start to produce winged forms, first females and later males, which fly off to the primary host, buckthorn. Here they mate and overwinter as eggs.


Ecology


Ant mutualism

Some species of
ant Ants are eusocial Eusociality (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...

ant
s farm aphids, protecting them on the plants where they are feeding, and consuming the honeydew the aphids release from the Rectum, terminations of their Gastrointestinal tract, alimentary canals. This is a Mutualism (biology), mutualistic relationship, with these dairying ants milking the aphids by stroking them with their antenna (biology), antennae. Although mutualistic, the feeding behaviour of aphids is altered by ant attendance. Aphids attended by ants tend to increase the production of honeydew in smaller drops with a greater concentration of amino acids. 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'') manage large herds of aphids that feed on roots of plants in the ant colony. Queens 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. An interesting variation in ant–aphid relationships involves Lycaenidae, lycaenid butterflies and ''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, since the caterpillars produce a pheromone which deceives the ants into treating them like ants, and carrying the caterpillars into their nest. Once there, the ants feed the caterpillars, which in return produce honeydew for the ants. When the caterpillars reach full size, they crawl to the colony entrance and form Cocoon (silk), cocoons. After two weeks, the adult butterflies emerge and take flight. At this point, the ants attack the butterflies, but the butterflies have a sticky wool-like substance on their wings that disables the ants' jaws, allowing the butterflies to fly away without being harmed. Some bees in coniferous forests collect aphid honeydew to make Honey#Honeydew honey, forest honey. Another ant mimicry, ant-mimicking gall aphid, ''Paracletus cimiciformis'' (Eriosomatinae), has evolved a complex double strategy involving two morphs of the same clone and ''Tetramorium'' ants. Aphids of the round morph cause the ants to farm them, as with many other aphids. The flat morph aphids are aggressive mimicry, aggressive mimics with a "wolf in sheep's clothing" strategy: they have hydrocarbons in their cuticle that mimic those of the ants, and the ants carry them into the brood chamber of the ants' nest and raise them like ant larvae. Once there, the flat morph aphids behave like predators, drinking the body fluids of ant larvae.


Bacterial endosymbiosis

Endosymbiosis with micro-organisms is common in insects, with more than 10% of insect species relying on intracellular bacteria for their development and survival. Aphids harbour a vertically transmitted (from parent to its offspring) obligate symbiosis with ''Buchnera aphidicola'', the primary symbiont, inside specialized cells, the bacteriocytes. Five of the bacteria genes have been transferred to the aphid nucleus. The original association may is estimated to have occurred in a common ancestor and enabled aphids to exploit a new ecological niche, feeding on phloem-sap of vascular plants. ''B. aphidicola'' provides its host with essential amino acids, which are present in low concentrations in plant sap. The metabolites from endosymbionts are also excreted in honeydew. The stable intracellular conditions, as well as the bottleneck effect experienced during the transmission of a few bacteria from the mother to each nymph, increase the probability of transmission of mutations and gene deletions. As a result, the size of the ''B. aphidicola'' genome is greatly reduced, compared to its putative ancestor. Despite the apparent loss of transcription factors in the reduced genome, gene expression is highly regulated, as shown by the ten-fold variation in expression levels between different genes under normal conditions. ''Buchnera aphidicola'' gene transcription, although not well understood, is thought to be regulated by a small number of global transcriptional regulators and/or through nutrient supplies from the aphid host. Some aphid colonies also harbour secondary or facultative (optional extra) bacterial symbionts. These are vertically transmitted, and sometimes also horizontally (from one lineage to another and possibly from one species to another). So far, the role of only some of the secondary symbionts has been described; ''Regiella insecticola'' plays a role in defining the host-plant range, ''Hamiltonella defensa'' provides resistance to parasitoids but only when it is in turn infected by the bacteriophage APSE, and ''Serratia symbiotica'' prevents the deleterious effects of heat.


Predators

Aphids are eaten by many bird and insect predators. In a study on a farm in North Carolina, six species of Passerine, passerine bird consumed nearly a million aphids per day between them, the top predators being the American goldfinch, with aphids forming 83% of its diet, and the vesper sparrow. Insects that attack aphids include the adults and larvae of predatory ladybirds,
hoverfly Hover flies, also called flower flies or syrphid flies, make up the insect family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is ...

hoverfly
larvae, parasitic wasps, aphid midge larvae, "aphid lions" (the larvae of green lacewings), and arachnids such as spiders. Among ladybirds, ''Myzia oblongoguttata'' is a dietary specialist which only feeds on conifer aphids, whereas ''Adalia bipunctata'' and ''Coccinella septempunctata'' are generalists, feeding on large numbers of species. The eggs are laid in batches, each female laying several hundred. Female hoverflies lay several thousand eggs. The adults feed on pollen and nectar but the larvae feed voraciously on aphids; ''Eupeodes corollae'' adjusts the number of eggs laid to the size of the aphid colony. Aphids are often infected by bacteria, viruses, and fungi. They are affected by the weather, such as precipitation (meteorology), precipitation, temperature and wind. Fungi that attack aphids include ''Neozygites fresenii'', ''Entomophthora'', ''Beauveria bassiana'', ''Metarhizium anisopliae'', and entomopathogenic fungi such as ''Lecanicillium lecanii''. Aphids brush against the microscopic spores. These stick to the aphid, germinate, and penetrate the aphid's skin. The fungus grows in the aphid's hemolymph. After about three 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 one that killed the aphid, but a secondary infection. Aphids can be easily killed by unfavourable weather, such as late spring freezes. Excessive heat kills the symbiotic bacteria that some aphids depend on, which makes the aphids infertile. Rain prevents winged aphids from dispersing, and knocks aphids off plants and thus kills them from the impact or by starvation, but cannot be relied on for aphid control.


Anti-predator defences

Most aphids have little protection from predators. Some species 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. For example, Alexander's horned aphids are a type of soldier aphid that has a hard exoskeleton and pincer (biology), pincer-like mouthparts. A woolly aphid, ''Colophina clematis'', has first instar "soldier" larvae that protect the aphid colony, killing larvae of ladybirds, hoverflies and the flower bug ''Anthocoris nemoralis'' by climbing on them and inserting their stylets. Although aphids cannot fly for most of their life cycle, they can escape predators and accidental ingestion by herbivores by dropping off the plant onto the ground. Others species use the soil as a permanent protection, feeding on the vascular systems of roots and remaining underground all their lives. They are often attended by ants, for the honeydew they produce and are carried from plant to plant by the ants through their tunnels. Some species of aphid, known as "woolly aphids" (Eriosomatinae), excrete a "fluffy wax coating" for protection. The cabbage aphid, ''Brevicoryne brassicae'', sequesters secondary metabolites from its host, stores them and releases chemicals that produce a violent chemical reaction and strong mustard oil smell to repel predators. Peptides produced by aphids, Thaumatins, are thought to provide them with resistance to some fungi. 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'' and the 2008 edition of the ''World Book Encyclopedia''. In fact, honeydew secretions are produced from the anus of the aphid, while cornicles mostly produce defensive chemicals such as waxes. There also is evidence of cornicle wax Kairomone, attracting aphid predators in some cases. Some clones of ''Aphis craccivora'' are sufficiently toxic to the invasive and dominant predatory ladybird ''Harmonia axyridis'' to suppress it locally, favouring other ladybird species; the toxicity is in this case narrowly specific to the dominant predator species.


Parasitoids

Aphids are abundant and widespread, and serve as hosts to a large number of parasitoids, many of them being very small (c. long) parasitoid wasps. One species, ''Aphis ruborum'', for example, is host to at least 12 species of parasitoid wasps. Parasitoids have been investigated intensively as biological control agents, and many are used commercially for this purpose.


Plant-aphid interactions

Plants mount local and systemic defenses against aphid attack. Young leaves in some plants contain chemicals that discourage attack while the older leaves have lost this resistance, while in other plant species, resistance is acquired by older tissues and the young shoots are vulnerable. Volatile products from interplanted onions have been shown to prevent aphid attack on adjacent potato plants by encouraging the production of terpenoids, a benefit exploited in the traditional practice of companion planting, while plants neighboring infested plants showed increased root growth at the expense of the extension of aerial parts. The wild potato, ''Solanum, Solanum berthaultii'', produces an aphid alarm pheromone, (E)-β-farnesene, as an allomone, a pheromone to ward off attack; it effectively repels the aphid ''Myzus persicae'' at a range of up to 3 millimetres. ''S. berthaultii'' and other wild potato species have a further anti-aphid defence in the form of glandular hairs which, when broken by aphids, discharge a sticky liquid that can immobilise some 30% of the aphids infesting a plant. 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 vigor in the plant, and aphid saliva is toxic to plants. Aphids frequently transmit
plant virus Plant viruses are virus A virus is a submicroscopic infectious agent In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processe ...

plant virus
es to their hosts, such as to potatoes, cereals, sugarbeets, and citrus , citrus plants. The green peach aphid, ''Myzus persicae'', is a vector for more than 110 plant viruses. Cotton aphids (''Aphis gossypii'') often infect sugarcane, papaya and peanuts with viruses. In plants which produce the phytoestrogen coumestrol, such as alfalfa, damage by aphids is linked with higher concentrations of coumestrol. The coating of plants with honeydew can contribute to the spread of fungi which can damage plants. Honeydew produced by aphids has been observed to reduce the effectiveness of fungicides as well. 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 an uninfested plant. However, this does not appear to be supported by observational evidence.


Sociality

Some aphids show some of the traits of eusociality, joining insects such as ants, bees, and termites. However, there are differences between these sexual social insects and the clonal aphids, which are all descended from a single female parthenogenetically and share an identical genome. About fifty species of aphid, scattered among the closely related, host-alternating lineages Eriosomatinae and Hormaphidinae, have some type of defensive morph. These are gall-creating species, with the colony living and feeding inside a gall that they form in the host's tissues. Among the clonal population of these aphids, there may be several distinct morphs and this lays the foundation for a possible specialization of function, in this case, a defensive caste. The soldier morphs are mostly first and second instars with the third instar being involved in ''Eriosoma moriokense'' and only in ''Smythurodes betae'' are adult soldiers known. The hind legs of soldiers are clawed, heavily sclerotized and the stylets are robust making it possible to rupture and crush small predators. The larval soldiers are altruistic individuals, unable to advance to breeding adults but acting permanently in the interests of the colony. Another requirement for the development of sociality is provided by the gall, a colonial home to be defended by the soldiers. The soldiers of gall-forming aphids also carry out the job of cleaning the gall. The honeydew secreted by the aphids is coated in a powdery wax to form "liquid marbles" that the soldiers roll out of the gall through small orifices. Aphids that form closed galls use the plant's vascular system for their plumbing: the inner surfaces of the galls are highly absorbent and wastes are absorbed and carried away by the plant.


Interactions with humans


Pest status

About 5000 species of aphid have been described and of these, some 450 species have colonized food and fiber crops. As direct feeders on plant sap, they damage crops and reduce yields, but they have a greater impact by being vector (disease), vectors of plant viruses. The transmission of these viruses depends on the movements of aphids between different parts of a plant, between nearby plants, and further afield. In this respect, the probing behavior of an aphid tasting a host is more damaging than lengthy aphid feeding and reproduction by stay-put individuals. The movement of aphids influences the timing of virus epidemics. Aphids, especially during large outbreaks, have been known to trigger allergic inhalant reactions in sensitive humans. Dispersal can be by walking or flight, appetitive dispersal, or by migration. Winged aphids are weak fliers, lose their wings after a few days and only fly by day. Dispersal by flight is affected by the impact, air currents, gravity, precipitation, and other factors, or dispersal may be accidental, caused by the movement of plant materials, animals, farm machinery, vehicles, or aircraft.


Control

Insecticide control of aphids is difficult, as they breed rapidly, so even small areas missed may enable the population to recover promptly. Aphids may occupy the undersides of leaves where spray misses them, while systemic insecticides do not move satisfactorily into flower petals. Finally, some aphid species are insecticide resistance, resistant to common insecticide classes including carbamates, organophosphates, and pyrethroids. For small backyard infestations, spraying plants thoroughly with a strong water jet every few days may be sufficient protection. An insecticidal soap solution can be an effective household remedy to control aphids, but it only kills aphids on contact and has no residual effect. Soap spray may damage plants, especially at higher concentrations or at temperatures above ; some plant species are sensitive to soap sprays. Aphid populations can be sampled using yellow-pan or Volker Moericke, Moericke traps. These are yellow containers with water that attract aphids. Aphids respond positively to green and their attraction to yellow may not be a true colour preference but related to brightness. Their visual receptors peak in sensitivity from 440 to 480 nm and are insensitive in the red region. Moericke found that aphids avoided landing on white coverings placed on soil and were repelled even more by shiny aluminium surfaces. Integrated pest management of various species of aphids can be achieved using biological insecticides based on fungi such as ''Lecanicillium lecanii'', ''Beauveria bassiana'' or ''Isaria fumosorosea''. Fungi are the main pathogens of aphids; Entomophthorales can quickly cut aphid numbers in nature. Aphids may also be Biological pest control, controlled by the release of natural enemies, in particular lady beetles and parasitoid wasps. However, since adult lady beetles tend to fly away within 48 hours after release, without laying eggs, repeated applications of large numbers of lady beetles are needed to be effective. For example, one large, heavily infested rose bush may take two applications of 1500 beetles each. The ability to produce allomones such as farnesene to repel and disperse aphids and to attract their predators has been experimentally transferred to transgenic ''Arabidopsis thaliana'' plants using an Eβf synthase gene in the hope that the approach could protect transgenic crops. Eβ farnesene has however found to be ineffective in crop situations although stabler synthetic forms help improve the effectiveness of control using fungal spores and insecticides through increased uptake caused by movements of aphids.


In human culture

Aphids are familiar to farmers and gardeners, mainly as pests. Peter Marren and Richard Mabey record that Gilbert White described an invading "army" of black aphids that arrived in his village of Selborne, Hampshire, England, in August 1774 in "great clouds", covering every plant, while in the unusually hot summer of 1783, White found that honeydew was so abundant as to "deface and destroy the beauties of my garden", though he thought the aphids were consuming rather than producing it. Infestation of the Chinese sumac (''Rhus chinensis'') by Chinese sumac aphids (''Schlechtendalia chinensis'') can create "Chinese galls" which are valued as a commercial product. As "Galla Chinensis", they are used in traditional Chinese medicine to treat coughs, diarrhea, diarrhoea, night sweats, dysentery and to stop intestinal and uterine bleeding. Chinese galls are also an important source of tannins.


See also

* Aeroplankton * Economic entomology * Pineapple gall


Notes


References


External links


Aphids of southeastern U.S. woody ornamentals

''Acyrthosiphon pisum''
MetaPathogen – facts, life cycle, life cycle image

Agricultural Research Service
Insect Olfaction of Plant Odour: Colorado Potato Beetle and Aphid Studies


Center for Invasive Species Research On the University of Florida / Institute of Food and Agricultural Sciences ''Featured Creatures'' website:
''Aphis gossypii'', melon or cotton aphid














{{Authority control Aphids, Agricultural pest insects Insect pests of temperate forests Insect pests of ornamental plants Insect vectors of plant pathogens Sternorrhyncha Extant Permian first appearances Insects in culture