   #copyright

Aphid

2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and
Fish

          "Aphid" is also the NATO reporting name for the Soviet/Russian
          Molniya R-60 air-to-air missile.

                                iAphids
                       Scientific classification

   Kingdom:     Animalia
   Phylum:      Arthropoda
   Class:       Insecta
   Order:       Hemiptera
   Suborder:    Sternorryncha
   Superfamily: Aphidoidea

                                  Families

   There are 10 families:
     * Adelgidae - adelgids, conifer aphids, Adelges cooleyi, Hemlock
       Wolly Adelgid, Adelges piceae
     * Anoeciidae
     * Aphididae
     * Drepanosiphidae
     * Homomasagymibutae
     * Greenideidae
     * Hormaphididae
     * Lachnidae
     * Mindaridae
     * Pemphigidae
     * Phloeomyzidae
     * Phylloxeridae
     * Thelaxidae

   Aphids, also known as greenfly, blackfly or plant lice, are minute
   plant-feeding insects in the superfamily Aphidoidea in the homopterous
   division of the order Hemiptera. Recent classification within the
   Hemiptera has changed the old term 'Homoptera' to two suborders:
   Sternorryncha (aphids, whiteflies, scales, psyllids...) and
   Auchenorryncha (cicadas, leafhoppers, treehoppers, planthoppers...)
   with the suborder: Heteroptera containing a large group of insects
   known as the 'true-bugs'; gnat bugs, pond skaters, shore bugs, toad
   bugs, water boatmen, backswimmers, etc.

   About 4,000 species of aphids are known, classified in 10 families; of
   these, 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 ladybugs ( 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 they 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 spreading from New
   Zealand to Tasmania. They have also been spread by human transportation
   of infested plant materials.

Anatomy

   SEM image
   Enlarge
   SEM image

   The most typical organ of aphids is their piercing-sucking mouthparts
   called stylets. They have soft bodies, long, thin legs, two-jointed,
   two-clawed tarsi, and usually a pair of abdominal tubes through which a
   waxy secretion is exuded. These tubes were formerly supposed to secrete
   the sweet substance known as " honeydew" so much sought after by ants;
   but this is now known to come from the alimentary canal. Both winged
   and wingless forms of both sexes occur; the wings when present are two
   pairs, lacy, transparent and only have one prominent longitudinal vein.
   Aphids also have a proboscis originating between and behind the
   forelegs. Aphids' antennae are composed of two thick basal segments and
   a flagellum with as many as four segments. The last of these four
   segments is divided into a proximal part and a thinner distal part
   (called process terminalis).

   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.
   They have two tarsal segments. The fifth abdominal segment bears a pair
   of tubes on the dorsal surface named siphunculi (cornicles), which are
   upright and point backward. A cauda is usually present below and
   between them on the last abdominal segment.

Diet

   Aphid life stages. (Aphis pomi)
   Enlarge
   Aphid life stages. (Aphis pomi)

   Many, but far from all, aphids are monophagous (i.e. 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 is forced into the food canal. Aphids
   actively 'drink' (suck) from xylem vessels when thirsty. 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 secrete; this is a
   mutualistic relationship. Aphid honeydew is rich in carbohydrates (like
   melezitose), 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 synthesizes some essential amino acids that
   are absent in the phloem that the aphids eat.

Reproduction

   Ant tending aphids
   Enlarge
   Ant tending aphids

   Apart from their importance from the economic standpoint, aphids are
   chiefly remarkable for the phenomena connected with the propagation of
   the species. For part or all of their life, most aphids are often found
   to be parthenogenetic. Aphids have been known to have what is called
   telescoping generations. With telescoping generations the female aphid
   will have a daughter within her who is already parthenogenetically
   producing its own daughter at the same time. This leads to the bizarre
   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 grand-daughters (Nevo and Coll 2001, Jahn et al.
   2005).

   At different times of the year, they can be viviparous or oviparous.
   During spring and summer, aphids are often parthenogenetic and
   viviparous and then give birth sexually during autumn. Therefore aphids
   are said to undergo cyclical parthenogenesis or to have a holocyclical
   life circle.

   Male and female aphids mate in autumn. Sexual females, but also asexual
   ones, have two sex chromosomes while sexual males only have one.

   The following brief summary of what takes place in the plant-louse of
   the rose ( Aphis rosae), 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 is 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. Likewise, in warm and tropical areas
   or during the growing season, aphids reproduce asexually without
   interruption. Since the young can become adults and reproduce within a
   few days, this process leads to the build-up of very large populations
   responsible for severe damage to crops and important economic losses;
   such populations often require pest control.
   P-14 lady beetle consuming an aphid
   Enlarge
   P-14 lady beetle consuming an aphid
   Aphids feeding on a rose bud, in the background lady beetle can be seen
   Enlarge
   Aphids feeding on a rose bud, in the background lady beetle can be seen

   Not the least interesting features connected with this strange
   life-history are the facts that 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 that the
   males only appear in any number at the close of the season. Although
   the factors which determine these phenomena are not clearly understood,
   it is 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 (host
   plant alternancy). 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.
   Aphid infestation on broccoli plant. Note that most of the aphids one
   sees in a plant infestation are juveniles.
   Enlarge
   Aphid infestation on broccoli plant. Note that most of the aphids one
   sees in a plant infestation are juveniles.

   Another widespread aphid in the Phylloxeridae family is Daktulosphairia
   vitifoliae (still frequently called by its former name Phylloxera
   vitifoliae), the famous Phylloxera which causes enormous loss by
   attacking the leaves and roots of grape vines. Its life-history is
   similar to that of Aphis rosae described above. In the autumn a single
   fertile egg is laid by apterous females in a crevice of the bark of the
   vine where it is protected during the winter. From this egg in the
   spring emerges an apterous female who makes a gall in the new leaf and
   lays therein a large number of eggs. Some of the apterous young that
   are hatched from these form fresh galls and continue to multiply in the
   leaves, others descend to the root of the plant, becoming what are
   known as root-forms. These, like the parent form of spring, reproduce
   parthenogenetically, giving rise to generation after generation of
   egg-laying individuals. In the course of the summer, from some of these
   eggs are hatched females which acquire wings and lay eggs from which
   wingless males and females are born. From the union of the sexes comes
   the fertile egg from which the parent form of spring is hatched.

   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 no aphids had died during the summer,
   there would be more than one and a half billion billion billion aphids
   (1.5 x 10^27) by the end of the season.

Evolution

   Aphids probably first appeared 280 million years ago, in the
   Carboniferous period. They probably fed on non-flowering 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.

   Aphids have not always looked like they do nowadays. Organs like the
   cauda or the siphunculi were not evolved until the Cretaceous.

Gallery

   Yellow aphid feeding on plant sap.

   Colony of Aphids.

   Aphid colors

   Lady beetle larva consuming an aphid
   Retrieved from " http://en.wikipedia.org/wiki/Aphid"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
