Because of their ability to rapidly increase in numbers by asexual reproduction and telescopic development, they are a highly successful group of organisms from an ecological standpoint.

[7] Aphids, and the closely related adelgids and phylloxerans, probably evolved from a common ancestor some 280 million years ago, in the Early Permian period.

[12] It has been hypothesized that the ancestors of the Adelgidae lived on conifers while those of the Aphididae fed on the sap of Podocarpaceae or Araucariaceae that survived extinctions in the late Cretaceous.

[20] Phylloxera (Daktulosphaira vitifoliae) are insects which caused the Great French Wine Blight that devastated European viticulture in the 19th century.

[26][27][28] Lachninae Hormaphidinae Calaphidinae Chaitophorinae Eriosomatinae (woolly aphids) Anoeciinae Capitophorus, Pterocomma Macrosiphini Rhopalosiphina Aphidina (Aphis spp)

[31] When host plant quality becomes poor or conditions become crowded, some aphid species produce winged offspring (alates) that can disperse to other food sources.

[34][35] Xylem sap is under negative hydrostatic pressure and requires active sucking, suggesting an important role in aphid physiology.

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.

[38] 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.

[54] 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.

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.

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.

[66]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.

The aphids are forced upwards and start to produce winged forms, first females and later males, which fly off to the primary host, buckthorn.

Aphids attended by ants tend to increase the production of honeydew in smaller drops with a greater concentration of amino acids.

[71] Another ant-mimicking gall aphid, Paracletus cimiciformis (Eriosomatinae), has evolved a complex double strategy involving two morphs of the same clone and Tetramorium ants.

[73] Aphids harbour a vertically transmitted (from parent to its offspring) obligate symbiosis with Buchnera aphidicola, the primary symbiont, inside specialized cells, the bacteriocytes.

[75] The original association is estimated to have occurred in a common ancestor 280 to 160 million years ago and enabled aphids to exploit a new ecological niche, feeding on phloem-sap of vascular plants.

[105] 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[106] and the 2008 edition of the World Book Encyclopedia.

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.

The hind legs of soldiers are clawed, heavily sclerotized and the stylets are robust making it possible to rupture and crush small predators.

The honeydew secreted by the aphids is coated in a powdery wax to form "liquid marbles"[124] that the soldiers roll out of the gall through small orifices.

[125] Insecticide control of aphids is difficult, as they breed rapidly, so even small areas missed may enable the population to recover promptly.

Moericke found that aphids avoided landing on white coverings placed on soil and were repelled even more by shiny aluminium surfaces.

[132] 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.

[136] 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.

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.

As "Galla Chinensis", they are used in traditional Chinese medicine to treat coughs, diarrhea, night sweats, dysentery and to stop intestinal and uterine bleeding.