Aphids are the most common insects found on trees, shrubs, and garden ornamental plants. Over 350 different aphid species occur in the state but most can feed on only a few species of plants. |
Aphids are small insects and few exceed 1/8-inch when full grown. They tend to have an oval body form and a pair of pipe-like cornicles usually can be seen protruding from the back of the body. Colors are widely variable among the different aphid species - ranging from very pale yellow to dark, nearly black. Most have shades of green or orange and a few species are even bright red. Upon close inspection, many aphids can be seen to have intricate body patterning.
Colonies of aphids often consist of a mixture of winged and wingless forms. The great majority of aphids usually develop into the wingless form to remain and reproduce on the plant. More winged forms tend to be produced when colonies get overcrowded, plants decline in quality, or environmental cues favor dispersal to new plants.
Essentially all aphids, regardless of their form, are females. Males, if they do occur, are present in late summer during only one of the many generations that are produced during a growing season. The normal habit of aphids is for a female to give live birth to a genetically identical daughter aphid through asexual reproduction called parthenogenesis. The newly born aphid can develop rapidly, typically becoming full-grown in about 10 to14 days. Adults usually can produce three to five young per day over the course of their lifetime, which may extend to about a month but is usually shortened by natural enemy activities.
Aphids are usually found feeding on the growing tips and undersides of leaves, where they congregate in large numbers. Open by the time they are noticed, the aphid colony has formed a dense cover on new leaves and stems. Though they weaken the plant, the most serious damage is inflicted by the viral and bacterial diseases they transmit. The most common symptom of aphid damage is curled, puckered and discoloured leaves. sometimes coupled with wilting. In addition, aphids exude honeydew, a sticky substance that encourages growth of sooty molds. This further damages the plant by shading the leaf surface and in severe infestations, feeding, disease and mold can combine to kill the plant. Physical and Cultural Controls
On shrubs and garden plants, aphids can sometimes be managed by simply washing them off of plants with a forceful jet of water. Hosing plants can lethally injure aphids and very few surviving aphids that are knocked to the ground can successfully find their way back onto their host plant.
Some flowers that are perennial, but dieback to the ground in fall, have problems with aphids in the spring. Columbine, lupines and perennial asters are examples. With these plants the eggs of the aphids are laid on the stems in fall, near the point where new shoots will emerge the following spring. Spring problems with these aphids can be prevented by removing the old top growth that contains the eggs before plants emerge in spring.
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