Membracidae: Wonder of terrestrial biodiversity.
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Species Gigantorhobdus enderleine
..............................Illustrated Identification Key to Assassin Bug Subfamilies & Tribes. Hemiptera: Reduviidae
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TREEHOPPER bugs are members of the family Membracidae, a group of insects related to the cicadas and the leafhoppers. About 3,200 species of treehoppers in over 400 genera are known. They are found on all continents except Antarctica; only three species are known from Europe. Individual treehoppers usually live for only a few months.
Treehoppers pierce plant stems with their beaks, and feed upon sap. The immatures can frequently be found on herbaceous shrubs and grasses, whereas the adults more often frequent hardwood tree species. Excess sap becomes concentrated as honeydew, which often attracts ants. Some species have a well-developed ant mutualism, and these species are normally gregarious, as well, which attracts more ants. The ants provide protection from predators. Treehoppers mimic thorns to prevent predators from spotting them.
Others have formed mutualisms with wasps, such as Parachartergus apicalis. Even geckos form mutualistic relations with treehoppers, with whom they communicate by small vibrations of the abdomen.
Eggs are laid by the female with her saw-like ovipositor in slits cut into the cambium or live tissue of stems, though some species lay eggs on top of leaves or stems. The eggs may be parasitised by wasps, such as the tiny fairyflies (Mymaridae) and Trichogrammatidae. The females of some membracid species sit over their eggs to protect them from predators and parasites, and may buzz their wings at intruders. The females of some gregarious species work together to protect each other's eggs. In at least one species, Publilia modesta, mothers serve to attract ants when nymphs are too small to produce much honeydew. Some other species make feeding slits for the nymphs.
Like the adults, the nymphs also feed upon sap, and unlike adults, have an extensible anal tube that appears designed to deposit honeydew away from their bodies. The tube appears to be longer in solitary species rarely attended by ants. It is important for sap-feeding bugs to dispose of honeydew, as otherwise it can become infected with sooty moulds. Indeed, one of the evident benefits of ants for Publilia concava nymphs is that the ants remove the honeydew and reduce such fungal growth.
Most species are innocuous to humans, although a few are considered minor pests, such as Umbonia crassicornis (a thorn bug), the three-cornered alfalfa hopper (Spissistilus festinus), and the buffalo treehopper (Stictocephala bisonia), which has been introduced to Europe. The cowbug Oxyrachis tarandus has been recorded as a pest of Withania somnifera in India.
The diverse morphological, behavioral, ecological, and distributional patterns among treehoppers make them an ideal group for exploring evolutionary relationships and the connections among form, function, genetics, the environment, and biogeography. The use of treehoppers as model organisms in evolutionary biology is ever increasing as evidenced by research in such areas as sympatric evolution, acoustic communication, host plant associations, biogeography, behavior, and evo-devo biology.
Recent phylogenetic studies are helping to unravel patterns in behavior and biogeography. For example, morphology-based analyses suggest that all Old World membracids (17 tribes) arose from two separate colonizations from the New World. These accidental colonizations set the stage for tantalizing “natural” experiments in evolution, running over millions of years, wherein treehopper lineages on opposite sides of the planet would radiate into parallel niches. This grand experiment, both spatially and temporally, brings to mind countless questions about key morphological and life history traits that may be addressed by comparing various attributes among Old and New World treehopper faunas.