This order contains a large and diversified group of species with complex life histories, involving bisexual and parthenogenetic generations. All species are plant feeders and some transmit disease. Distinguishing characteristics include the attitude of the wings at rest; they are usually held roof-like over the body, with the inner margins overlapping slightly at the apex (Slide). In some groups one or both sexes may be wingless, or both winged and wingless individuals may occur in the same sex (Slide). Metamorphosis is simple.
Family Cicadidae. Cicadas are medium to very large (16-80 mm.) insects easily recognized by their characteristic shape (Slide). The immature stages are subterranean and feed on the sap of roots of various trees and shrubs. The periodical cicada, or 17-year locust Magicicada septendecim, usually appear in huge swarms every 13 or 17 years in the southeastern United States and at this time the ovipositing females may seriously damage twigs and branches of forest and shade trees by cutting slits in the bark for oviposition sites.
Family Cercopidae. Spittlebugs are small (<10 mm.), squat, frog-like insects resembling the leafhoppers, but differing in the spines on the hind tibiae. They are also closely related to the Cicadidae. The nymphs of many species surround themselves with a frothy, spittle-like mass (Slide). The pine and Saratoga spittlebugs are often serious plantation pests in eastern and southern North America.
Family Cicadellidae. Leafhoppers resemble spittlebugs, but have one or more rows of small spines extending the length of the hind tibiae in contrast to one or two stout spines in the cercopids. They are small, slender, active insects (Slide). Both nymphs and adults have the characteristic habit of running sideways. Leafhoppers are of great importance for their transmission of many plant diseases, such as phloem necrosis of elm.
Aphids are characterized by having a complex system of alternating generations including wingless, winged, parthenogenetic and sexual forms in a single life cycle (Slide). There are several important families in this group.
Family Adelgidae. Gall aphids, woolly aphids. The gall aphids are minute or very small wingless and winged insects with soft, fragile bodies (Slide). The body is often covered with waxy threads, and the wings are held roof-like over the body when at rest. The members of this group feed only on conifers, living on practically all portions of the tree, and often forming galls. The most destructive adelgid pest is the balsam woolly aphid, Adelges piceae, a European species accidentally introduced into North America. Infestations are characterized by a whitish flocculence on the trunk and branches (Slide), a gouty swollen condition at the tips of twigs (Slide), and/or an abnormal growth of dense brittle, brown sapwood called "rotholtz" on the main trunk of trees (Slide). The balsam woolly aphid has caused extensive destruction of fir (Abies) forests in many parts of North America (Slide).
Another common adelgid is the Cooley spruce gall aphid, Adelges cooleyi, which forms characteristic galls on spruce trees (Slide). The Cooley spruce gall aphid has a complex life cycle with generations alternating between spruce, where galls are formed, and Douglas-fir on which the aphid is free-living.
Family Aphididae. Aphids, plant lice, green flies. The aphids are a large group of small, soft-bodied, pear-shaped insects (Slide). Wax secretion is typically less than in adelgids, but most aphids secrete honeydew from the anus. Honeydew is a favorite food for ants which are often good indicators of the presence of aphids (Slide). A black smut-like fungus frequently grows on the honeydew. The life cycle of many aphids is complex. The typical aphid overwinters as an egg on the primary host; wingless, parthenogenetic females hatch in the spring and in a short time produce a similar generation (Slide). Several wingless parthenogenetic generations may follow, until a winged parthenogenetic generation gives rise to the sexual forms that produce the overwintering eggs. Probably no hardwood or coniferous tree species is exempt from aphids. Damage is variable, only occasionally serious, as in white pine plantations in northeastern North America.
Female scale insects are always wingless, extremely sluggish or completely fixed in position, with a hard epidermis or covered with a waxy secretion of variable thickness or with a definite round, oval or elongated shell (the scale). The waxy secretion is usually whitish and powdery or cotton-like. The various coverings protect them against natural enemies and chemical sprays. The males are small and delicate, wingless or with one pair of wings. The life cycle is relatively simple, usually completed on the same host. The female is responsible entirely for the injury to the plants. Many of the species excrete honeydew.
Family Coccidae. Soft scales. Female soft scales are soft, convex, spherical scales that usually colonize twigs and branches. The female produces abundant cotton-like wax, which entirely covers the body (Slide). Many species are phytophagous and are sometimes problems on ornamental trees, but rarely in forests. An exception is the beech scale, introduced from Europe, and responsible for the beech bark disease that has ravaged eastern beech forests (Slide)
Family Diaspididae. Armored scales are characterized by formation of a thick protective shell or scale above, and usually by a very thin layer beneath the body. No honeydew is excreted. The pine needle scale (Slide) and black pineleaf scale (Slide) are of considerable importance in forestry (Slide), particularly in dense, overstocked stands.
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