Aphids are small sap-sucking
insects and members of the
superfamily Aphidoidea. Common names include greenfly and blackfly,
[a] but the insects can also be brown or pink, and the group includes the fluffy white
woolly aphids. A typical life cycle involves flightless females giving living birth to female
nymphs 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 colonise 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 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, colonising many plant groups. About 5,000 species of aphid have been described, all included in the family Aphididae. Around 400 of these are found on food and fibre crops, and many are serious pests of
forestry, as well as an annoyance for
gardeners. So-called dairying
ants have a
mutualistic relationship with aphids, tending them for their
honeydew, and protecting them from
Aphids are among the most destructive insect pests on cultivated plants in temperate regions. Not only do they weaken the plant by sucking sap, but they act as
plant viruses and disfigure ornamental plants with deposits of honeydew and the subsequent growth of
sooty moulds. Because of their ability to rapidly increase in numbers by
asexual reproduction, they are a highly successful group of organisms from a zoological 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
aphid midge larvae,
lacewing larvae, and
Biological pest control as part of an
integrated pest management strategy is possible but difficult to achieve except in enclosed environments such as glasshouses.