An aphid is sap-sucking insect that can infest vegetables, fruit, flowers, woody plants, trees and even weeds. There are more than 200 hundred species of aphids, also called plant lice. Most are about 1/8 inch long. An aphid's body is pear-shaped and soft, and it has long legs and antennae. Some aphids have wings, but more do not. An aphid can be black, green, red, yellow or brown, according to the species, or it can look waxy or woolly due to substances it excretes over its body.
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Where You Might See an Aphid
You will rarely see one aphid by itself. This insect lives in clusters of tens or hundreds. The places you're most likely to see aphid clusters is on new shoots and leaves, but they also appear on roots, branches, twigs and flowers. Some aphid species infest only one type of plant, while others can appear on a wide range of plants.
Signs of an Aphid Infestation
Some types of aphid are the same color as the plants they infest, so you may notice signs of an aphid infestation before you see the aphids. Signs of an aphid infestation include distorted leaves and stems, and a clear, sticky coating called honeydew, which aphids excrete. A black sooty mold grows on honeydew.
Ants "farm" aphids, eating their sticky honeydew. They protect aphids from predators and move them to new plants. If you see a line of ants going up and down a plant or tree, it may be infested with aphids.
In areas that don't experience frosts, aphids appear year-round. In colder zones, infestations appear in spring and continue through the growing season. Aphids lay tiny, shiny black eggs. In cold areas, the eggs survive in nooks and crannies through winter and hatch out when temperatures rise in spring. In some aphid species, immature or adult aphids overwinter.
Aphid life cycles differ among types, but many female aphids reproduce asexually, with no need for a male. One female can produce five or six nymphs a day. An aphid nymph is an immature aphid. Aphid nymphs can mature into adults in eight to 12 days. When a plant becomes too crowded, winged aphids, which fly away to find new plants, are produced.
A severe aphid infestation causes poor growth and plant dieback.
Some Common Types of Aphid
An aphid is often named for the plant it infests. Some common aphids include the bean aphid, which is black; the cabbage aphid, which looks waxy; and the green peach aphid, which is green. The green peach aphid infests a wide range of crops including the annual vegetables spinach (Spinacia oleracea), carrot (Daucus carota var. sativus ), lettuce (Lactuca sativa) and corn (Zea mays). The bean aphid and green peach aphid also infest woody ornamental plants.
The potato aphid is another common aphid. The adults are green but the nymphs are orange-red. The potato aphid infests spinach and lettuce as well as potatoes (Solanum tuberosum).
The crapemyrtle aphid is light green, and the rose aphid is brown-gray. The woolly apple aphid is covered in a white coating like cotton wool, but the green apple aphid is bright green.
Aphids by State
Aphid types and populations vary across the United States. For example, in Minnesota, the green peach aphid, potato aphid and the cabbage aphid are common, while in Pennsylvania the rose aphid, green peach aphid, melon aphid and white pine aphid are often seen. In Utah, apple trees are commonly infested by the woolly apple aphid, the green apple aphid and rosy apple aphid.