Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Order Hemiptera
Common names: bugs, leafhoppers, cicadas, aphids, lerps, scales
Overview
The Hemiptera are a large and frequently encountered order, members of which are extremely diverse in size, shape and colour. They include insects commonly known as bugs, leafhoppers, cicadas, aphids, lerps and scale insects. The most distinctive feature of hemipterans is their sharply pointed, tube-like mouthparts (proboscis or rostrum) that are used for piercing or sucking. Hemipterans usually have two pairs of wings; however, some groups may be wingless and others have only forewings. Hemipterans range in size from 1�110 mm in length and nymphs typically look like small, wingless adults although they may differ in colour and markings. The order is divided into four suborders:
1) Heteroptera (true bugs) that have the forewings are hardened at the base, membranous at the tips, and sitting flat over the abdomen, hiding the membranous hindwings; the head and proboscis can flex forward and some predatory species have raptorial forelegs.
2) Auchenorrhyncha (cicadas, spittlebugs, leafhoppers, planthoppers and treehoppers) that have the forewings uniform in texture and held like a tent over the abdomen; the head and proboscis are directed down and back and many have hind legs adapted for jumping.
3) Sternorrhyncha (psyllids, whiteflies, aphids, mealy bugs) that are usually small, soft bodied and generally wingless; the head and proboscis are directed down and back, and in some the legs are vestigial or absent. Many species cover themselves with wax to prevent their soft bodies from desiccating.
4) Coleorrhyncha (moss bugs), a small, rarely seen, group of flattened, mostly flightless bugs that are found amongst mosses and liverworts.
Distribution and diversity
Hemipterans occur in a wide range of terrestrial and freshwater habitats across the globe; they are widely distributed across Australia. The Coleorrhyncha consists of a single Gondwanan family (Peloridiidae). Approximately 80,000 hemipteran species are described worldwide. About 4,500 species are described for Australia, but the true size of the faun is estimated to be >11,500 species.
Life cycle
Sperm transfer is direct in hemipterans. Many species stridulate, producing sound to communicate between the sexes. Eggs are normally attached to vegetation, or embedded in plant tissue, litter or soil. Some species guard their eggs and scale insect females protect their eggs under the body. After hatching, nymphs typically grow quickly through 2�6 instars. In many species, the nymphs are gregarious, often aggregating in large numbers, especially in the first instar. In some species, such as cicadas (Cicadidae), the nymphs look very different from the adults as they are specialised for burrowing and can remain in the ground for several years. Nymphs moult 6�8 times, depending on the species, before they attain maturity. Many aphids are parthenogenetic during part of their life cycle.
Feeding
All species of Hemiptera feed on fluids � generally on plant fluids. Some are predators of other invertebrates or bloodsuckers of mammals and birds. The proboscis of hemipterans contains cutting blades and a two-channelled tube. They feed by cutting into plant or animal tissue, then sending saliva down one of the tubes to begin digestion. The liquid food is then sucked up the other tube. Typically, adults and nymphs feed on the same material. Some, such as male scale insects, do not feed as adults.
Ecology
Almost all hemipterans are terrestrial, although some species of Heteroptera inhabit freshwater, living either in the water or on its surface. Some also live in the littoral and intertidal zones. Most plant-feeding hemipterans are found on leaves, stems or bark of plants, others feed on the roots. Many Sternorrhyncha form protective waxy secretions or hard galls, particularly on the leaves and stems of Acacia and Eucalyptus. Herbivorous species range from being highly specific in host plant selection to widely polyphagous. Many species are well camouflaged, using colour, patterns, structures or behavioural traits to blend in with their surroundings. Some flash warning colours, release noxious chemicals or bite when threatened. Many hoppers (Auchenorrhyncha) have partnerships with ants in which the hoppers provide honeydew (a sugar-rich liquid excretion) to the ants and, in return, the ants provide protection from predators. Some hemipteran species are active or ambush predators, sucking internal fluids of prey, such as eggs, larvae or adults of other invertebrates; fish-killer bugs (Belostomatidae) have been known to eat small fish and tadpoles. Bed bugs (Cimicidae) and some assassin bugs (Reduviidae) are external parasites that suck the blood of mammals and birds. Hemiptera are important agricultural pests and are known to cause direct damage to crops and ornamental garden plants by herbivory, and indirectly, by transporting diseases, such as plant viruses. Predatory Hemiptera are used and encouraged in agricultural systems to control insect pests.
Hemiptera from Two People's Bay, Western Australia
Image credit: Photographer: Mark Harvey
� Western Australian Museum
Water Scorpion (Laccotrephes sp.) from southeastern Queensland, Australia
Image credit: Photographer: E.S. Volschenk
� Western Australian Museum
Lerps formed by a member of the Psylloidea
Once mature, the adults have devloped wings and leave the lerp
Image credit: � John Jennings
