HOMOPTERAN

Newly emerged adult cicada (Tibicen pruinosa). any member of the order Homoptera, a large group of sucking insects. The members exhibit considerable diversity in body size and number more than 32,000 species. All of the Homoptera are plant feeders, with mouthparts adapted for sucking plant sap from a wide assortment of trees and wild and cultivated plants. Many homopterans cause injuries or destruction to plants, including fruit trees and grain crops; others are vectors of plant diseases, but a few provide secretions or other products that are beneficial and have commercial value. Most members of the Homoptera fall into one of two large groups; the Auchenorrhyncha, which consists of the cicadas (see photograph), treehoppers, froghoppers or spittlebugs, leafhoppers, and planthoppers or fulgorids; and the Sternorrhyncha, which includes aphids or plant lice, phylloxerans, coccids, scales, whiteflies, and mealybugs. Newly emerged adult cicada (Tibicen pruinosa). a member of the insect order Homoptera, which includes some 32,000 species of sucking insects. Homopterans are divided into two main suborders: the Auchenorrhyncha include the cicadas (see photograph), spittlebugs, treehoppers, leafhoppers, and planthoppers; the Sternorrhyncha include the aphids, scale insects, white flies, and mealybugs. A third suborder, Coleorrhyncha, consists of a single family of primitive forms. Homopterans all feed on plant juices, frequently causing considerable damage. They are worldwide in distribution. The evolutionary history of Homoptera is a matter of debate, as is their correct taxonomic classification. Homopteran fossils dating back to the Late Permian Epoch (258 to 245 million years ago) have been found. Most homopterans are between 4 and 12 mm (0.16 and 0.5 inch) in length, although certain cicadas (family Cicadidae) and the lanternfly (Lanternaria phosphorea; see ) can reach 8 cm (3.1 inches). At the other extreme, male scale insects may only reach 0.5 mm. In all homopterans the beak, or proboscis, is adapted for piercing plants and sucking their juices; consisting of the mandibles and maxillae with extensible stylets, the beak is firmly attached to the ventral margin of the head. The first pair of wings may be pigmented or transparent, and they occasionally have waxy surfaces. The hindwings are always membranous. When closed, the forewings sit over the back like a peaked roof. One pair of compound eyes is typical, but some male scale insects have three pairs. Visual sensitivity varies in the order, being greatest in leafhoppers and treehoppers, less important in cicadas and aphids, and almost nonexistent in the mealybugs and scale insects. Most homopterans live on plant sap, which contains much water. In order to obtain sufficient nutrients they must process large amounts of sap. There is a filter chamber in the gut that traps excess water and excretes it, along with some sugars and waste, as a substance known as honeydew. This is attractive to other insects, such as ants, that subsist on sweetened nutrients. Some ants farm certain species of aphids, carrying them to their food plants and feeding on the exuded honeydew. Most species of homopterans have specific types of plants on which they feed. These preferences determine the habitats in which various species are found; some may occur only on white oaks in deciduous forests, others on rabbitbrush in deserts or on blueberry bushes in bogs. The moisture in the microhabitat is also important, and the nymphs of many species feed on the undersides of leaves where the stomata, through which transpiration occurs in plants, maintain a slightly higher relative humidity. Many aphids lead a subterranean existence, feeding on the roots of plants. Young cicadas and some immature leafhoppers are other underground root feeders. Homopterans are the object of many predaceous and parasitic insects. Ladybird beetles feed on aphids and scale insects; an adult ladybird can consume several thousand aphids in a period of a few months. Aphidlion larvae and flower flies also feed on aphids. Dryinid wasps parasitize various leafhoppers and treehoppers, the larvae developing within the host insect. The cicada-killer wasp (Sphecius speciosus) paralyzes a cicada by stinging it, places it at the bottom of a burrow, and lays her eggs on it; then she covers the burrow. The larvae hatch and grow on the cicada until they emerge as adults the following year. Most homopterans reproduce sexually, and the females lay eggs. Metamorphosis is typically gradual; immature stages lack wings but otherwise resemble the adults. Most homopterans have a short life cycle and produce at least one generation per year. Eggs are generally laid on (among Sternorrhyncha) or in (Auchenorrhyncha) the preferred food plant, so that the newly hatched young have food immediately available. Some leafhoppers (e.g., Gyponana mali) overwinter as eggs inside the twigs of various trees. Others, such as Empoasca recurvata, hibernate in the adult form. Most leafhoppers have only one generation a year. White flies (Aleyrodidae), common pests of citrus trees and in greenhouses, produce several generations per year in warm climates. The aphids are soft-bodied insects that generally form dense populations. They usually overwinter as eggs that hatch into females. These females reproduce parthenogenetically and give birth to living female young. Late in the season they produce males also. Mating occurs, and new eggs are laid that overwinter and repeat the cycle. Scale insects also depart from the usual reproductive pattern. Most overwinter as eggs under the scale covering of the female. The newly hatched are active crawlers and wander off in search of food. Within a few days they molt their legs and antennae and secrete a hard scale. Thereafter females increase in size but do not change their form. In the males, however, the last preadult stage develops wings, and after the final molt the male can fly in search of females. The best-known homopterans are the periodical cicadas, especially the 13- and 17-year forms. Early in the spring the orange-winged adults mate, following which the female, using her powerful ovipositor, lays her eggs within the wood of deciduous trees. After several weeks the young hatch, drop to the ground, and dig into the soil. They spend the next 13 or 17 years underground, feeding on sap from the roots of trees. After the proper number of years the mature nymph emerges from the soil, climbs a tree, and attaches itself firmly to the bark. A split appears in the skin of the back and the adult slowly crawls out. Many homopterans cause economically significant damage to crops and ornamental plants. Plants may be harmed directly by feeding methods. Some leafhoppers (Cicadellidae) secrete a salivary substance that causes the destruction of chlorophyll and death of the leaf. Spittlebugs, or froghoppers (Cercopidae), may stunt a crop severely by intensive feeding. Cicadas damage fruit-bearing trees when they make slits in the twigs for egg deposition. Many homopterans are carriers of bacterial and viral plant diseases. On the positive side, some of the wax-secreting insects are commercially important. The female Indian lac insect, Laccifer lacca, secretes great amounts of lac that coat the twig she rests on; this coating may be over one inch in thickness. The lac is melted off the twigs, refined, and used to prepare shellac and varnish. Additional reading Z.P. Metcalf and Virginia Wade, A Bibliography of the Homoptera (Auchenorhyncha), 2 vol. (1942), General Catalogue of the Homoptera, 8 vol. in 48 (195471), Fulgoridae of Eastern North America (1923), taxonomic treatment with keys to families and excellent illustrations; K.C. Doering, Synopsis of the Family Cercopidae (Homoptera) in North America, J. Kans. Ent. Soc., 3:5364, 81108 (1930), a synoptic treatment of all known North American cercopids; P.B. Lawson, The Cicadidae of Kansas, Kans. Univ. Sci. Bull., 12: 309376 (1920), taxonomic and distributional discussion of Kansas cicadas; P.W. Oman, The Nearctic Leafhoppers (Homoptera: Cicadellidae): A Generic Classification and Check List (1949); H. Osborn, The Membracidae of Ohio (1940), taxonomy of treehoppers of Ohio and proximity; D.L. Crawford, Monograph of the Jumping Plant Lice or Psyllidae of the New World (1914), a taxonomy of jumping plant lice of North America; G.F. Ferris, Atlas of the Scale Insects of North America, 7 vol. in 6 (193755, reissued 1973), a comprehensive study of genera and species, excellent illustrations; A.D. MacGillivray, The Coccidae (1921), synoptic treatment of scale insects; F.C. Hottes and T.H. Frison, The Plant Lice or Aphididae of Illinois (1931), aphid taxonomy; J.W. Evans, A Natural Classification of Leafhoppers (Jassoidea, Homoptera), 3 pt. (194647), a taxonomy of leafhoppers with emphasis on higher categories. Dwight Moore DeLong