I have been seeing large aphid populations on crape myrtles. Aphids are soft-bodied, slow-moving insects that reproduce rapidly. Their color can vary from green to brown to red to black. They may be winged or wingless, but wingless forms are most common in Oklahoma. They have piercing-sucking mouthparts and feed by sucking sap from plant tissues.
The life cycle of a typical aphid species may produce several wingless generations in the spring, followed by a generation of winged forms. The winged forms can fly to other plants where many more wingless summer generations can be produced. Aphid populations can increase rapidly in extremely short periods of time. During warm weather some species can complete a generation in less than two weeks.
Many aphids prefer to feed on young, succulent growth. Some feed in sheltered locations, such as inside leaves that they have caused to curl or become distorted. Aphids attack trees and shrubs of all kinds, but do not usually seriously injure them. New plant growth may become distorted or stunted before predators and parasites decimate the aphid population. Aphids and other plant sap sucking insects excrete large amounts of honeydew, a sticky substance often seen on leaves, pavement, automobiles and other surfaces below the infested foliage. Honeydew consists mainly of excess sugars ingested by the insects and passed through the body. Ants are often attracted to the sugary honeydew and occasionally tend the aphids much like people tend cattle: some ants even carry the aphids to new plant parts to establish more colonies.
Sometimes a black fungus called sooty mold will grow on the honeydew deposited on foliage below aphid colonies. This fungus can detract from the plant's appearance and reduce the amount of light reaching the leaves, thus reducing photosynthesis.