Aphids cluster sometimes by the hundreds on stems and underneath leaves sucking the sap from the leaf causing it to curl up and wither. Aphids are about 1/4" long, either wingless or winged and can be green, yellow, brown, pink, gray, or black. Sometimes they are covered in a fluffy white wax as in the woolly apple aphid.
Aphids have many generations a year. Young aphids are called nymphs. They molt, shedding their skins about four times before becoming adults. There is no pupal stage. Some species mate and produce eggs in fall or winter, which provides them a more hardy stage to survive harsh weather. Most species over winter as fertilized eggs glued to stems or other parts of plants. Nymphs which hatch from these eggs become wingless females known as stem mothers. They mature in 7 — 10 days and then are ready to produce live young. Each is capable of producing 40 — 60 offspring.
In some cases, these eggs are laid on an alternative host, usually a perennial plant, for winter survival. All offspring are females which soon mature and begin to reproduce in the same manner. This pattern continues for as long as conditions are favorable.
Periodically, some or all of the young develop wings and migrate to other plants. Some species always settle on the same type of plant; others have one or more alternate hosts. With the return of autumn's shorter days and cooler temperatures, a generation appears which includes both males and females. After matting, these females lay the fertilized eggs which over winter and eventually hatch into stem mothers the following spring.
Aphids can transmit viruses to the plant.
Beneficial insects, such as lady beetles and lacewings, will begin to appear on plants with moderate to heavy aphid infestations. These beneficial insects may eat large numbers of aphids but the reproductive capability of aphids is so great that the impact of the natural enemies may not be enough keep these insects at or below acceptable levels.
Aphids can be controlled with horticultural oil in winter that destroy aphid eggs on deciduous fruit trees and bushes. They can also be dislodged with a strong blast of water directly on them or by using insecticidal soap.
Aphids are in the order Homoptera, Family Aphididae.