- The Singing Cicadas
- 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.
-
- 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.
- --------------------------------------------------------------------------------
-
- gordon@earthlife.net
© Earth-Life Web Productions
Bringing Insects to the World http://www.earthlife.net/insects/
-
-
-
|
|