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antipodi
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Wed Apr 26, 2006 12:45 pm
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An Overview of Cicadas
In Australia you really know its summer when the deafening roar of this incredible insect starts...so here is some info on this endearing creature
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Introduction
The word Cicada derives directly from the Latin Cicada, in Greek they are called Tettix.
Insects are thought by some people to be quite similar to mankind and it was with this thought in mind that J.G.Myers in his lovely book "Insect Singers" wrote the following.
"It will not therefore surprise one to find the greatest musical artists of the insect world among its deepest drinkers."
Their sudden appearance in the hottest season of the year, their mysterious feeding habits, and above all their striking musical performances have attracted mankind's attention to the Cicadas for thousands of years.
Cicadas are members of the Hemiptera, then the Homoptera, the Homoptera is often considered an order in its own rite these days but in some books you will find it designated as a suborder of the Hemiptera. They are then members of the superfamily Cicadoidea, and the Family Cicadidae, or in the case of two unusual Australian species Family Tettigarctidae. There are about 1500 species of Cicada in the world, some of the largest are in the genera Pomponia and Tacua. Cicadas are mainly warm-temperate to tropical in habitat. There are 202 species in Australia compared with about 100 species in the Palaearctic and only one species in the UK. The British species is Melampsalta montana (was Cicadetta) which is widespread outside of the UK and occurs up to 61o north. It seems to prefer pines, though old larval skins exuviae have been found on grass stems and occasionally Bracken Pteridium aquilonia.
Generally speaking cicadas have life cycles that last from one to several years, most of this time is spent as a nymph under the ground feeding on the xylem fluids of plants by piercing their roots and sucking out the fluids. Some species take a very long time to develop and the periodical cicadas of the genus Magicicada of North America are well known because some of them have a 17 year life cycle.
Periodical Cicadas
There are 3 species of periodical cicada, each of which has two forms, a 17 year form and a 13 year form; they are M. septendecim, M. septendecula and M. cassini. Some authorities claim that the 13 year form of each species should be a species in its own rite, in this case they are named; M. tredecim, M. tredecassini and M. tredecula. Of the three species (called Decim, Cassini and Decula for short) Decim is the most common in the north of their range, Decula is rare all over and Cassini is commonest in the Mississippi valley. In addition to this, the 13 year broods tend to be centrally placed within the Cicadas distributional range and the 17 year forms are found more to the North, East and West. It is possible for populations to switch between the 13 and 17 year lifecycles for various reasons. Populations can be tracked depending on their emergence times and it is possible for populations to be reproductively isolated because of their different emergence years. Populations are designated broods depending on the timing of their cycle, there are therefore seventeen 17-year broods and thirteen 13-year broods, the 17-year broods are named in roman numerals I - XVII and the 13-year brood XVIII - XXX. An interesting fact arising from all this is that the respective 17 and 13 year broods of any one species only overlap once every 221 years, i.e. broods V and XXII emerged synchronously in 1897 and will not do so again until 2118. Periodical cicadas tend to emerge between late April and early June, both males and females congregate in choruses for the first couple of weeks to sing and mate, the females disperse to lay their eggs, the eggs take 6-8 weeks to hatch and like all cicadas head straight for the soil. It has been estimated that in some cases 98% of the hatching nymphs die in the first 2 years of life.
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Reproduction
Unlike most Homopterans, Cicadas tend to be both facing in the same direction during copulation. Copulation as not often been observed in many species, female Melampsalta leptomera a New Zealand grass laying species, has been observed to mate successively between egg laying bouts. Copularion takes about 1 hour in Cicadatra querula.
Egg Laying
The eggs are long this cylinders slightly pointed at one end. One female may lay 400–600 eggs in the periodical cicadas and 500-600 in Tibicen plebia. All known cicada eggs are inserted into plant material. Eggs are laid into what are called 'eggnests' each of which contains a small number of eggs and is cut into the plant material by the female using her ovipositor. The eggs turn salmon pink prior to hatching and the nymphs are normally a similar colour on hatching.
Females of Magicicada septendecim can be observed testing the tree they are on for suitability before laying eggs. First she grasps the twig with her forelegs measuring its size. Twigs between which are not between 3mm and 11mm in diametre are generally rejected. Secondly by dragging her proboscis over the twig and perhaps inserting it she is tasting the tree for secondary compounds such as those found in Pines or Black Cherry which will normally result in the tree being rejected. Thirdly by probing with her ovipositor she is testing how hard the wood is, thus by testing the tree and by observing the presence of other ovipositing females a female makes her decision whether or not to lay.
The eggs of cicadas are longer than broad and oval in shape. The females have a saw like ovipositor with which they dig a hole/crevice in some plant material. Normally this is either the plant species the larvae will be able to feed on, or a plant near to the larval food plant. The female takes some time to create her nest and in areas where cicada populations are high partially constructed and abandoned nests may be found in various stages of construction. Females lay several eggs per nest and some species line the nest with a sort of foam which hardens and gives added protection to the eggs. In Magicicada septendecim, which uses a number of host plants but prefers Box Elder, the female constructs the nest with two chambers. One chamber is made first and filled with eggs and then the second chamber is made and also filled with eggs. The result appears to be a 2 sided chamber filled with eggs, however if the female is disturbed during egg laying she will leave the nest partially finished. There is some evidence to suggest that females will abandon nest attempts on some tree species more regularly than on others, but the causes for this are not well understood.
Nymphs
Cicada nymphs are all very similar, the head is more conically produced (sticks out forwards more) than those of the adults and they possess a strong rostrum. The antennae are also longer and stouter than in the adults, being particularly large in the first instar. Ocelli are functionally absent and the prothorax is well developed in order to support the large fossorial forelegs. Later instars have conspicuous wingpads. The abdomen is fat and segmented. Nymphs are encased in a membrane on hatching, only the front legs are free, which they use to drag themselves out of the nest and then fall to the ground. They immediately bury themselves in search of a root on which to start feeding.
They feed on plant roots digging deeper into the soil and using larger roots in successive instars. Feeding, in both nymphs and adults, is done by penetrating the XYLEM not phloem as is the case with most sap sucking insects. This gives them a very watery, low sugar and high amino acid diet. The larvae build themselves cells to live in, often using the excess excreted moisture resulting from their feeding to cement the walls of their cells together. Generally cicada nymphs go through 5 instars.
When they are ready to emerge as adults the nymphs return to near the soil surface and construct a waiting cell. Mostly these cells are immediately below the surface but they may be as far as 30 to 60 cm down. These cells are often accompanied by a turret constructed of soil particles which are glued together and erected above the soil surface. In some place these may be 6 inches (15cm) high and occur at a density of 25 per square foot (30cm2). The exit hole can be at the base of the turret giving it a blind tower for a roof. They remain in this cell until the weather conditions are right for it to emerge. The nymph then climbs up some nearby vegetation and at a certain variable height emerges from his old skin into a beautiful flying and singing machine. The time from emergence to being able to fly is about 2-3 hours in larger species but can be as quick as 30 minutes in smaller ones. There is a tendency for species to emerge in the evening but some species emerge in broad daylight.
Adults
Adults feed on Xylem the same as the nymphs and this means that like other sap feeding insects they have excess fluids, mostly water as xylem fluid is low in sugars, to get rid of while feeding, this allows Diceroprocta apache a desert species found in Arizona USA to use evaporation as a cooling method, allowing it better survive the high temperatures experienced in this habitat.
Cicadas such as Magicicada septendecim exhibit a broad selection of host trees and it has been suggested, though not explained, that this is facilitated by the fact that the nymphs feed from the xylem rather than the phloem.
Cicadas have good eyesight and good hearing, most adult cicadas are wary animals and use their wings to escape the attention of us humans. A few species, such as the New Zealand Melampsalta leptomera, a species which feeds on Maram Grass use the more traditional homopteran response to a threat of dropping to the ground and feigning death. Larger species will shriek if picked up and the resulting vibration can be quite surprising.
Singing
Most male Cicadas sing (i.e. produce sound), this is primarily what brings them to our attention, in most cases, as far as I know the songs are sufficiently distinct to be of use in taxonomy. Cicadas nearly always sing from a position of rest, normally on a piece of vegetation but sometimes as in Okanagana palidula from a hole in the ground. Singing while in flight is extremely rare though it has bee recorded from few species. Cicadas usually sing in a sunny spot, and normally only on sunny days. In the past the reluctance of cicadas to sing on damp days was said to be because their singing membranes were wet an thus not working. This is now known not to be the case. Cicadas sing by using special muscles to buckle the 'timbals' (special ribbed chitinous membranes) located on the upper-side of their 1st abdominal segment. Cicadas make more than one sound, for instance male Fidicina mannifera from Peru make 4 different sounds; a disturbance sound, a call, a low amplitude song and their main song. In this species the males also engage in a stereotyped visual display called a 'parallel walk'. This involves two males first calling back and forth then lining up on a tree trunk, facing up the tree and then walking side-by-side up the trunk occasionally jostling one another for about 25 cm. This interesting action generally occurs between a territory holding male and an intruder. In most cases it is the intruder who flies away at the end of the 'parallel walk'
Predators
Many generalist insectivores feed heavily on emerging nymphs, which in periodical cicadas emerge in huge numbers in emergence years, every 13 or 17 years. This periodical life cycle makes it very difficult for predators or parasite to specialise on these species of cicadas because for most they are only available once in a number of generations and not in between. The only know specialist parasite of periodical cicadas is the fungus Massospora cicadina. This flooding of the market for short periods of time is an unusual method of dealing with predators called ' Predator Satiation ' basically this means that when the cicadas are around there are just too many of them for their predators to deal with and in this way some survive to breed, other insects such as mayflies, ants and termites also indulge in this mass synchronised emergence strategy. Ants are known to take a heavy toll of newly hatched nymphs.
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Antipodi
May one day man and Animals live together in harmony and peace
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