Everything about Aphid totally explained
» "Aphid" is also the NATO reporting name for the Soviet/Russian Molniya R-60 air-to-air missile.
Aphids, also known as
plant lice, are small plant-feeding
insects, members of the superfamily
Aphidoidea. About 4,000 species of aphids are known, presently classified in 10 families, though historically there were many fewer, with most species 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 size from 1-10
mm long.
Important natural enemies include the predatory
lady beetles (
Coleoptera:
Coccinellidae),
hoverfly larvae (
Diptera:
Syrphidae), and lacewings (
Neuroptera:
Chrysopidae), and
entomopathogenic fungi like
Lecanicillium lecanii and the
Entomophthorales.
Aphids are distributed world-wide, but are most common in
temperate zones. It is possible for aphids to migrate great distances (mainly through passive dispersal riding on winds) depending on the weather patterns; for example, the lettuce aphid spread from
New Zealand to
Tasmania. They have also been spread by human transportation of infested plant materials.
Taxonomy
Aphids are in the
superfamily Aphidoidea in the homopterous division of the order
Hemiptera. Recent classification within the Hemiptera has reduced the old taxon "Homoptera" to two suborders:
Sternorrhyncha (aphids,
whiteflies,
scales,
psyllids...) and
Auchenorrhyncha (
cicadas,
leafhoppers,
treehoppers,
planthoppers...) with the suborder
Heteroptera containing a large group of insects known as the "
true bugs". More recent reclassifications have resulted in a substantial rearrangement of the constituent families with the Aphidoidea, with some old families reduced to subfamily rank (for example,
Eriosomatidae), and numerous old subfamilies elevated to family rank.
Anatomy
Aphids contain sucking mouthparts called
stylets. They have soft bodies; long, thin legs; two-jointed, two-clawed tarsi; and usually a pair of cornicles, abdominal tubes through which droplets of defensive fluid are exuded.
Aphids have two compound eyes and two ocular tubercles made up of three lenses, each of which is located behind and above the compound eyes. When host plant quality becomes poor or is crowded, female aphids will produce winged offspring that can disperse to other food sources.
Diet
Many, but far from all, aphids are monophagous (for example feeding only on 1 species of plant). Others, like
Myzus persicae feed on hundreds of plant species across many families.
Similarly to related families, aphids passively feed on
sap of
phloem vessels in plants. This sap being kept under high pressure, once a phloem vessel is punctured, it's forced into the food canal. As they feed, aphids often transmit
plant viruses to their food plants. These viruses can sometimes kill the plants.
Some species of
ants "farm" aphids, protecting them on the plant they eat, and eating the
honeydew that the aphids release from their
anus; this is a
mutualistic relationship. Aphid honeydew is rich in carbohydrates, of which the aphids ingest an excess, being phloem-feeders. Many aphids are host to
endosymbiont bacteria,
Buchnera, which live in specialized cells called
bacteriocytes inside the aphid. These bacteria synthesize some essential
amino acids that are absent in the phloem that the aphids eat.
Reproduction
Aphids are known for having unusual reproductive adaptations in some species. Many aphids undergo
cyclical parthenogenesis. In the spring and summer, only females are present in the population. 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, and give live birth to 1st instar nymphs (viviparous). Aphids typically live from 20-40 days and thus undergo multiple parthenogenetic, viviparous generations each summer. In
the fall, a change in
photoperiod and temperature cause females to parthenogenetically produce sexual females and males. The males are genetically identical to their mothers except they've lost one sex chromosome. Sexual females and males mate and females lay eggs that will develop outside of the mother. Thus in the fall aphids undergo sexual, oviparous reproduction. The aphids will overwinter as eggs and hatch out as females in the following spring.
Aphids have been known to have what is called
telescoping generations. The parthenogenetic, viviparous female aphid will have a daughter within her, who is already parthenogenetically producing her own daughter at the same time. This leads to the situation where the diet of a female aphid can have inter-generational effects on the body size and birth rate of aphids. In other words, what the aphid eats can directly change the size and fertility of the aphid's daughters and granddaughters (Nevo and Coll 2001, Jahn et al. 2005).
The following is the life cycle of the rose aphid (
Aphis rosae), and may be regarded as typical of the family, though exceptions occur in other species: Eggs produced in the autumn by fertilized females remain on the plant through the winter and hatching in the spring give rise to female individuals which may be winged or wingless. From these, females are born parthenogenetically: that's to say, without the intervention of males, and by a process that has been compared to internal budding, large numbers of young resembling their parents in every respect except size are produced, which themselves reproduce their kind in the same way. This process continues throughout the summer, generation after generation being produced until the number of descendants from a single individual of the spring-hatched brood may amount to many thousands. In the autumn winged males appear; union between the sexes takes place and the females lay the fertilized eggs which are destined to carry the species through the cold months of winter. If, however, the food-plant is grown in a glasshouse or greenhouse where protection against cold is afforded, the aphids may go on reproducing agamogenetically (asexually) without cessation for many years.
The young may be born by the oviparous or viviparous methods and either gamogenetically or agamogenetically, and may develop into winged forms or remain wingless, and males only appear in any number at the close of the season. Although the factors which determine these phenomena are not clearly understood, it's believed that the appearance of the males is connected with the increasing cold of autumn and the growing scarcity of food, and that the birth of winged females is similarly associated with decrease in the quantity or vitiation of the quality of the nourishment imbibed. Sometimes the winged females migrate from the plant they were born on to start fresh colonies on others often of quite a different kind. Thus the
apple aphid (
Aphis mali), after producing many generations of apterous females on its typical food-plant, gives rise to winged forms which fly away and settle upon grass or corn-stalks.
Some species of cabbage aphids (like
Brevicoryne brassicae) reproduce rapidly during the summer. They are all females, and can produce up to 41 generations of offspring. If none of these died, a female would have more than one and a half billion billion billion offspring (1.5 x 10
27) by the end of the season.
Evolution
Aphids probably first appeared around 280 million years ago, in the
Carboniferous period. They probably fed on plants like
Cordaitales or
Cycadophyta. The oldest known aphid
fossil is one of the species
Triassoaphis cubitus from the
Triassic. There were relatively few species of aphids at that time, and the number of species only considerably increased since the appearance of
angiosperms 160 millions of years ago. This is due to the fact that angiosperms provide an occasion for aphids to become specialized. Organs like the
cornicles didn't appear until the
Cretaceous.
Gallery
Image:Aphids on broccoli.jpg|left|thumb|Aphid infestation on broccoli plant.
Image:Aphids-on-lupine1.jpg|right|thumb|Lupine stalk infested with aphids
Image:Aphidoidea fight.jpg |2 aphids fighting
Image:Aphidoidea puceron Luc Viatour.jpg
Image:Aphid-sap.jpg |Yellow aphid feeding on plant sap.
Image:Aphid-sap2.jpg | Aphid- note defensive fluid excreted by the cornicles.
Image:Sa aphid colony highres dustfree.jpg |Cluster of aphids.
Image:Aphids 01.JPG |Aphids under attack on a thistle
Image:Aphid-colored.jpg |Aphid colors
Image:Aphid-attack.jpg |Lady beetle larva consuming an aphid
Image:Aphid_infestation.jpg|Aphid Infestation on Sunflower
Image:Aphids.jpg|Aphids on rose foliage
Image:Aphid-giving-birth.jpg|Aphid giving birth to live young
References
G. B. Buckton, British Aphides (Ray Soc. 1876-1883)
Nevo, E., and M. Coll. 2001. Effect of nitrogen fertilization on Aphis gossypii (Homoptera: Aphididae): variation in size, color, and reproduction. J. Econ. Entomol. 94: 27-32.
Jahn, GC, LP Almazan, and J Pacia. 2005. Effect of nitrogen fertilizer on the intrinsic rate of increase of the rusty plum aphid, Hysteroneura setariae (Thomas) (Homoptera: Aphididae) on rice (Oryza sativa L.). Environmental Entomology 34 (4): 938-943.(External Link
)
Further Information
Get more info on 'Aphid'.
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