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Homoptera (True bugs - Order: Hemiptera)

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A photograph of a cicada nymph.

Some species of cicada have 13 or 17 year cycles. The nymphs live underground, when the adults finally emerge, they all do so at the same time.
Photograph: USDA

The second sub-order of the Hemiptera is a rather mixed bag of insects which look quite different from the Heteroptera but they all have certain features to do with their mouthparts in common. The homopterans include cicadas, aphids and scale insects.

Entomologists regard homopterans as being of two types:

The Auchenorrhyncha

Among the Auchenorrhyncha, the cicadas are generally large (at least 15mm long) and have two pairs of membraneous wings held above the body like a tent. The adults feed by inserting their beaks into twigs or branches on trees, but the young larvae live underground. In Britain, there is probably only one species of cicada, found in the south of England.

Cicadas in the genus Magicicada in north America are known as periodic cicadas - they have very long lifecycles. There are four species of 13-year cicadas and three 17-year cicadas. The nymphs of the 17-year cicadas live underground for 17 years, feeding on roots. During this time their development is slow, and they only go through seven instars. When the adults finally emerge, they all do so at the same time, which results in millions of adult cicadas suddenly appearing together - an awe-inspiring sight!

The adults produce a species-specific sound using two membranes called tymbals, and when they emerge after 13 or 17 years the noise is deafening. The adults mate very quickly and the females lay their eggs which drop to the ground, and when the nymphs hatch they burrow underground - where they stay for another 17 years!

It has been suggested that the length of time these periodic cicadas live in the immature stage may be related to the life-cycle of their potential predators during evolution. Thirteen and seventeen are both prime numbers (whole numbers that are only divisible by themselves and by one) and it would be difficult for a predator to regulate its lifecycle to co-evolve with the 13 or 17-year cicadas.

Froghoppers are also known as spittle bugs or cuckoo-spit insects, and they belong to the family Cercopidae. In some cases their nymphs live underground, but the nymphs that are found in cuckoo-spit produce the frothy protective material to stop themselves from drying up and being eaten by predators.

The leafhoppers (Cicadellidae) are found on leaves and resemble narrow froghoppers. Like the froghoppers they can jump to avoid danger, and they also fly readily. Some leafhoppers produce honeydew. The candy-striped leafhopper Graphocephala Fennahi is an American leafhopper that has become naturalised in Britain and other European countries, and is found on rhododendron.

The remainder of the Auchenorrhyncha belong to the superfamily Fulgoroidea, the planthoppers, the largest family of which (the Delphacidae) contains over 70 British species.

The Sternorrhyncha

The psyllids (superfamily Psylloidea) are small or very small insects that look like mini cicadas. They are also known as jumping plant lice, and many of them deform leaves or cause plants to form galls.

There are more than 4,000 species in the superfamily Aphidoidea and these are the insects known as aphids, plant lice, greenfly and blackfly. They have the ability to reproduce at a fast rate and as they feed on the sap of young shoots and leaves this makes them serious pests. Most aphids are 2-3mm long and they are mainly green or brown in colour. Many species have wingless forms and those with wings usually hold them tentlike above the body.

A photograph of an ant tending a large number of aphids (blackfly)

Ants 'farm' aphids and protect them from predators such a ladybirds. In return the ants collect sugary honeydew from the aphids.

Their lifecycle through the year starts with an overwintering phase as eggs, somewhere on the host plant. In the spring, wingless females emerge which can reproduce by parthenogenesis - i.e. without sexual reproduction. They give birth to numerous live young nymphs every day. These nymphs are slightly different from the mother, and some of them will have wings.

Throughout the summer there are a number of generations of these parthenogenetic females, the winged forms alternating with wingless ones. The winged form is responsible for spreading the species from plant to plant. As autumn approaches, the females start to give birth to males as well as females, and after mating the females lay the eggs which overwinter, to hatch as females the following spring.

Among the other members of the Sternorrhyncha is a group of atypical insects in the superfamily Coccoidea, known as scale insects and mealybugs. There are around 170 species in Britain. The females of many species in this group are wingless and even legless: they remain motionless, attached to their foodplant by their beak. They are covered by a hard waxy scale.

The males look more like insects; they are usually winged, with the hindwings reduced to halteres, as in the Diptera. However, the males are rarely seen, so what we know about these creatures is based mostly on our knowledge of the females.

Like the aphids, the scale insects produce many young in a generation, and parthenogenesis and viviparity (giving birth to live nymphs rather than laying eggs) is commonplace. The newborn nymphs are mobile, but lose their legs after their first moult.

Scale insects can be serious pests, capable of killing whole trees. They are easily transported from place to place on plant material and they have spread around the world. An example of biological control of these pests is the Fluted Scale (Icerya purchasi) which was introduced to America from Australia. It was controlled by releasing large numbers of the predator ladybird beetle Rodolia cardinalis.

Essential reading from the Amateur Entomologists' Society

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