Diversity Cercopoidea

Cercopoidea (froghoppers and spittlebugs, Fig. 1) are characterized by the following combination of morphological characters: head with frontoclypeus inflated; median ocellus absent; ocelli on crown distant from margin; pronotum extended to scutellar suture; body clothed with fine setae; hind coxae conical, tibia without rows of setae but often with one or more conspicuous spines; male subgenital plate present. The super-family comprises four families Aphrophoridae, Cercopidae, Clastopteridae, and Macherotidae. The first Cercopoidea (Procercopidae) appear in the fossil record during the Lower Jurassic. These insects retained a median ocellus and apparently lacked the dense setal covering of modern cercopoids. Aphrophoridae and Cercopidae did not appear until the middle Cretaceous; Clastopteridae and Machaerotidae apparently arose during the Tertiary.

Approximately 2500 species and 330 genera of Cercopoidea have been described. The classification has not been revised in over 50 years, and the phylogenetic status of most cercopoid genera and higher taxa remains unknown. Cercopidae [Fig. 1(1)], the largest family, differs from Aphrophoridae [Fig. 1(3)], the next largest, in having the eyes slightly longer than wide and the posterior margin of the pronotum straight (instead of emarginate). The small families Machaerotidae and Clastopteridae differ from other Cercopoidea in having a well-developed appendix (distal membrane) on the forewing. Machaerotidae [Fig. 1(2)] differ from Clastopteridae [Fig. 1(4)] in having two or more r-m crossveins in the forewing and in lacking an outer fork on the radial vein of the hind wing.

Production of "spittle" is a unique characteristic of Cercopoidea [Fig. 1(5)]. Nymphs of Machaerotidae produce the froth during molts, while in other families nymphs live permanently surrounded by the froth. The lateral parts of nymphal abdominal segments are extended ventrally into lobes, which form an open or closed (in machaerotids) ventral cavity, filled with air. The nymphs introduce bubbles of air into their liquid excretion by bellowslike contractions of this device; periodically the tip of the abdomen is extended through the surface of spittle mass to channel air into the cavity. The same air supply is used for breathing via spiracles that open into the ventral cavity. The froth is stabilized by the action of the secretory products manufactured in the highly specialized Malpighian tubules of the nymphs and mixed into the main watery excreta. Wax secreted by plates of epidermal glands on the sixth through eighth abdominal terga (Batelli glands) may also help stabilize the froth.

The function of the spittle mass is not completely understood. It is usually assumed that it protects the insect from predators and desiccation. Cercopoid nymphs are sessile and live within the spittle mass (or, in Machaerotidae, inside fluid-filled tubes). In some species, nymphs tend to aggregate, forming large spittle masses containing hundreds of individual nymphs. Nymphs of Cercopidae apparently feed on roots, whereas aphrophorid and clastopterid nymphs occur on aboveground parts of their host plants. Nymphs of the Machaerotidae live immersed in liquid inside tubes cemented to the twigs of their host plants. The tubes are constructed from calcium carbonate and other salts secreted by the midgut and an organic matrix secreted by the Malpighian tubules. Adult cercopoids do not produce spittle and are free living. They cannot run, and often use only the front and middle legs to walk, dragging the extended hind legs. Consequently, they rely mostly on their strong jumping and flying abilities for movement.

Species of Cercopoidea are often restricted to particular habitats, but many if not most seem to be capable of utilizing a variety of host plants. Many species seem to prefer actinor-rhizal and other nitrogen-fixing hosts, presumably because the xylem sap of such plants contains more amino acids and is more nutritious. Cercopoidea is a predominantly tropical group, occurring mostly in wet and mesic habitats. Nevertheless, the genus Clastoptera, has radiated extensively in north temperate North America, and Aphrophora comprises numerous arboreal species throughout the Holarctic. Cerco-pidae are primarily grassland insects, feeding on grasses and other herbs. The family Aphrophoridae includes both grassfeeding and arboreal species. Machaerotidae and Clastop-teridae are primarily arboreal.

Members of the superfamily Cercopoidea occur worldwide. Cercopidae and Aphrophoridae are pantropical in distribution, with relatively depauperate faunas in the Holarctic. Machaerotidae are restricted to the Oriental and Australian regions. Clastopteridae are mostly New World animals, but one small genus, possibly misclassified, occurs in the oriental region. Most tribes are restricted to either the New or the Old World, and phyletic diversity seems to be highest in the oriental region. A few genera (e.g., Philaenus and Aphrophora) are widespread, partly as a result of human activities, but most are restricted to a single biogeographic realm.

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