Introduction to the Auchenorrhyncha

The term Auchenorrhyncha refers to a group of insects within the Hemiptera (true bugs) that includes the leafhoppers (Cicadellidae), planthoppers (Delphacidae, Cixiidae, Tettigometridae and Issidae), froghoppers (Aphrophoridae and Cercopidae), treehoppers (Membracidae) and cicadas (Cicadidae). They are found in a wide range of habitats and can be very numerous in some of them, for example grasslands.

The Auchenorrhyncha are distinguished from other Hemiptera by having a uniform forewing structure that is either membranous or hardened but never divided into two sections as in the Heteroptera, mouthparts that emanate from the base of the head, three tarsal segments (compared to one or two segments in aphids and related groups) and three antennal segments. They feed exclusively on plant sap which they extract with their sucking mouthparts and there are nearly 400 species in the British Isles. Some species will be familiar to the general naturalist; the ‘spittle’ masses (often referred to as ‘cuckoo-spit’) created by the immature stages (nymphs) of froghoppers are a familiar sight in spring on a variety of plants and the strikingly coloured red and green ‘Rhododendron leafhopper’ Graphocephala fennahi is well known to gardeners in southern Britain where it can reach alarmingly high densities on Rhododendrons, although it does them little harm. The attention of visitors to marshes and fens is often drawn by two of our largest and most brightly coloured leafhoppers; the green and blue Cicadella viridis and the yellow and black striped Evacanthus interruptus.


Graphocephala fennahi	Cicadella viridis female (l) and male (r)	Evacanthus interruptus

Life cycles

The Auchenorrhyncha are hemimetabolous insects, meaning that their life cycle lacks a pupal phase between the immature and adult stages, unlike the majority of other insects such as beetles, butterflies, moths, flies, ants, bees and wasps. Instead, their immature stages (usually referred to as nymphs rather than larvae) look like smaller wingless versions of the adults. Typically, they go through five nymphal ‘instars’, each progressively larger than the previous one and requiring them to moult their skin in order to grow. Eggs are usually laid directly into the tissue of their chosen plant, just under the surface of the leaf or in the stem. Most species take four to six weeks, depending upon the weather, to progress from the first instar to the adult stage.

The vast majority of species complete either one or two generations each year; a few are able to complete several generations a year when the weather is particularly favourable, whilst most cicadas take several years to reach maturity. A few species over-winter as adults, but most pass the winter either as eggs or nymphs.

Feeding and host plant preferences

The Auchenorrhyncha feed by extracting the contents of their host plant’s tissues. Although the majority of species tap into the transport system and extract fluids from the phloem, some of the larger species, such as cicadas, members of the Cicadellinae (e.g. Cicadella viridis) and the froghoppers (Aphrophoridae) feed on xylem sap. The fact that this resource is under considerable negative pressure means that these insects require powerful muscles to pump it out, explaining their characteristically bulbous faces.

Members of the Typhlocybinae (a sub-family of the Cicadellidae) extract the contents of mesophyll cells. Extensive feeding by this group produces a characteristic stippling on the leaves of their host-plants which often reveals their presence.

Feeding signs of Eupteryx urticae on stinging nettle.

Different species vary considerably in terms of the number of plant species they feed on. The Common Froghopper Philaenus spumarius is one of the most generalist insect herbivores known, having been recorded feeding on at least one hundred different plant species. At the other end of the spectrum, there are many specialist species that feed on only one species of plant. In fact, the more we study these insects, the more we tend to find that they are more specialised in their feeding habits than we previously thought.

A very wide range of plant groups is exploited by these insects, although some families are favoured more than others. Grasses, sedges and to a lesser extent rushes support many species, including all of the Delphacidae in Britain and many Cicadellidae. A wide range of deciduous tree species are exploited, with particularly rich assemblages on oaks, birches, poplars and willows. The majority of the Typhlocybinae feed on trees, although there are a few genera on herbaceous plants or grasses and sedges. Some species of cicadellids feed on grasses and other low-growing plants as nymphs and then migrate up into the tree canopy when they become adult. Certain groups show clear ecological differentiation between genera in terms of the plant groups that they exploit. Thus, within the froghoppers or spittlebugs (Aphrophoridae), Philaenus spumarius is a generalist on herbaceous plants, Neophilaenus species feed on grasses and rushes, while Aphrophora species are mostly found on trees.

None of the Auchenorrhyncha in this country cause serious problems for agriculture, although minor cosmetic damage sometimes occurs to garden plants such as roses and horticultural crops such as potatoes and tomatoes. Further afield however, especially in tropical countries, the group includes some of the world’s most serious agricultural pests on rice, maize, cotton and many other crops. Some species transmit viruses between plants which can cause as much or more damage than the direct extraction of sap by feeding.


Left: The Common Froghopper Philaenus spumarius, a generalist on many herbaceous plants. Middle: Eupteryx florida, a typhlocybine species feeding on a range of herbaceous plants in the Lamiaceae. Right: Alebra albostriella, a typhlocybine species feeding only on pedunculate oak.

Locomotion

As the name suggests, leafhoppers and planthoppers are conspicous by being able to jump strongly. Froghoppers in particular have very powerful hindlegs and are able to jump higher than fleas relative to their size.

Many Auchenorrhyncha species, particularly delphacids, can have different wing forms as adults and may be either long-winged (macropterous) or short-winged (brachypterous). Fully-winged individuals are capable of flight and can travel large distances. The proportion of these forms in any given population varies considerably, based on the species concerned and the population density. For species that tend to be short-winged, ecological pressures such as overcrowding or poor habitat quality will cause nymphs to develop into long-winged forms, allowing dispersal and colonisation of new areas.

Eurybregma nigrolineata (brachypterous form)

Eurybregma nigrolineata (macropterous form)

Communication

Auchenorrhyncha are unusual in that the sexes communicate with each other using species-specific acoustic signals produced by a unique structure on the side of the abdomen called the ‘tymbal’ organ. Taxonomists have used detailed analyses of the composition of these signals to distinguish between closely-related species that may appear identical in other respects. In most cases, these calls take the form of vibrations, inaudible to the human ear, sent through the plant.

On the other hand, cicadas communicate through the air, males producing some of the loudest ‘songs’ of all insects, as visitors to Mediterranean countries in summer can testify. Only one cicada is known from Britain, the ‘New Forest Cicada’ Cicadetta montana, but regrettably this species is now feared to be extinct.

Predators

Auchenorrhyncha are very abundant in many habitats and provide a food source for numerous other animals. Their main predators are probably spiders, birds and a range of insects. The Wasp Spider Argiope bruennichi is now a common species in grasslands throughout much of southern Britain and spins large orb webs which frequently capture jumping and flying arthropods such as Auchenorrhyncha. Other generalist predators include damselbugs (Hemiptera, Nabidae), a number of plant bugs (Hemiptera, Miridae), predatory flies such as robberflies (Diptera, Asilidae) and ants.

A number of solitary wasps (Hymenoptera, Crabronidae) are interesting specialist predators which stock their nest burrows solely with Auchenorrhyncha. Gorytes and Argogorytes species prey on froghoppers, while Mimesa species collect leafhoppers.


A solitary wasp in the genus Gorytes with the froghopper Aphrophora alni	The damselbug Nabis flavomarginatus with the leafhopper Cicadella viridis.	The Hornet Robberfly Asilus crabroniformis with the planthopper Javesella pellucida

Parasites and Parasitoids

There are a variety of parasites and parasitoids of Auchenorrhyncha, including pipunculid flies, dryinid wasps, stylops and mites. Specimens parasitized by dryinid wasps (Hymenoptera, Dryinidae) are frequently encountered in the field and are easily recognized by the sacculi emerging from the abdomen. These wasps are external parasitoids of both adults and nymphs and the forelegs of females bear hooks (chelae). These are used to grip the host which is stung and temporarily paralysed before an egg is inserted between the thoracic and abdominal segments. Upon hatching the larva forms a cyst through which it derives nutrition from the host and as it grows the late instar larva is visible within a sac projecting from the abdomen. The end of larval development coincides with the death of the host and the fully-grown larva emerges to pupate in the soil.

Nymph of Errastunus ocellaris with Dryinid larva

The larvae of pipunculid flies (Diptera, Pipunculidae) and stylops (Stresispera) develop within the body of their hosts and are also regarded as parasitoids, since they usually bring about its death.

It is also not unusual to find Auchenorrhyncha which are parasitized by very small red mites (Arachnida, Acari). These are not usually detrimental to the survival of the host unless they affect particularly small species or are present in large numbers.

The presence of parasites can cause marked changes to the form of the genitalia and hence has important implications for identification. In some cases it may not be possible to use the genitalia of infested specimens for species determination.

Dicranotropis hamata female with a parastic mite