Каминяр Дмитрий Генаддьевич : другие произведения.

I. Akimushkin. The cicadas, the aphids, the scale insects

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Homopterans [A. Bloch]
   Some systematics unites the bugs with cicadas, aphids, scale insects, leafhoppers and whiteflies into one suborder, the rhynchota or the hemipteroida. The others consider all of the abovementioned insects, except for the bugs, into a separate order of homopterans. This double meaning signifies, firstly, the fact that the front and hind wings of the homopterans are equally hard. Usually, if an insect has front and back pairs of wings, the front pair is harder than the hind one. Secondly, the mouth of the homopterans has changed into a sucking tube, with which they drink sap after piercing a plant.
   The ancient representatives of this order are known from the Permian period of the Palaeozoic epoch (280--255 MYA).
   Currently more than 30 thousand species of the homopteran insects is known to science.
   Who struggles to imagine the general appearance of a cicada, he can look at pictures or photos. Many of the cicadas have legs specialized for jumping. They can hop... Here in Russian literature an interesting shift in the names has occurred. Here is the tale of the academic M.S. Gilyarov (The author will start at the end to be closer to the subject of the discussion, and will finish with the start of the quote).
   'Not everyone knows that in the fable of I.A. Krylov 'The Dragonfly and the Ant' the word 'dragonfly' goes to the cicada, unfortunately. Dragonflies do not jump (while the cicadas have jumping legs), do not sing (the cicadas sing) and etc - every aspect of the fable that is connected to the dragonfly does not fit it, but fits the cicada. The thing is that Krylov used the plot and the imagery of the famous French fable author Lafontaine (and Lafontaine used the plots of the An-cient Greek fables of Aesop). In Lafontaine's homeland cicadas' song and the cicadas themselves are known to everyone, while on Russia's north, under Petersburg, they are practically absent. I.A. Krylov did not know entomology all that well and translated the word 'cigale' ('cicada') as 'dragonfly'.
   Now let us get back to the beginning of the curious tale:
   'In the tropics... their songs resemble the sound of a circular saw, and in South America and in India the sounds emitted by the cicadas are as loud as the piercing whistle of a train. Only the males emit the sounds, they on their undersides of the first segment of the abdomen have a pair of bulging plates - the cymbals... The sound is caused by the shift in the cymbals' bulge - according to the same principle, as the sounds emitted by a tin can with a bulging bottom, if that bottom is squeezed by fingers and released in turns... The cicadas' song is considered beautiful in many countries (in Indonesia, in France)'.
   Let us also add that the ancient Greeks too loved the cicadas' song (and the Romans hated it!) and that the aforementioned cymbals emit up to 600 waverings in a second!
   'Happy are cicadas lives, because they've got voiceless wives' (Xeno of Rhodes).
   He is not quite right, though: after the cicadas were examined by the means of modern technol-ogy, new data was received. And here is what is apparently going on:
   '...in 1959 G. Shtrubing reported his observations about the 19 species of European cicadas. Both genders sing in their cases, however the human ear lacks the necessary technological means to hear the females' singing' (Peter Richel).
   The female lays eggs under the bark of twigs or at the end of leaves. The larvae, as soon as they hatch from the eggs, fall down and dig underground (up to a meter in depth!). After becoming a nymph, i.e. a larva of advanced age that is about to become an adult cicada, they crawl upwards: to the entrance into the burrow. Here, if a flood threatens, if rains have come, they dig a side tunnel in the burrow; it branches off from the main tunnel of the burrow angling upwards.
   They wait for their upcoming metamorphosis into a cicada. How much, however, did they live as larvae underground waiting for this hour? A lot. The common Russian cicada lives as a subterranean larva for 4 years. That cannot be compared in any way to the longetivity of the North American 'seventeen-year-old' cicada (in Russian scientific literature it is often presented with the name of 'periodical'): it lives for 17 years underground! That is in the north and northeast of its habitat, in the south and south-west - only 13 years. But even such longetivity is a lot for a creature that, once it becomes an adult, becomes a sexually mature cicada instead of a larva, lives above ground for just a month or one and a half.
   The common Russian cicada that lives in the woodland on the south of our country is 10 cm in the wingspan, but in tropics there are cicadas with wingspans up to 18 cm!
   The cicadas cannot be compared with anything not just in longetivity (among insects), but also in the strength of their songs. Forget about the grasshoppers, locusts, crickets - the cicadas suppress them all with the volume of their 'music'.
   All cicadas only drink plant sap. They have plenty of sugar but little protein. No creature on Earth can live long without protein. In 1951 G. Muller examined 369 species of cicadas from 15 families. Every one of them, in the different segments of the abdomen, possessed myocetomas - 'gardens', inhabited by symbiotic bacteria and mushrooms. They feed on the sap that is delivered to them by the cicadas' blood. Working them over, the symbionts enrich the cicadas with protein.
   However an excess of sugar still remains. This the rhynchotes remove from the organism. Nature has invented several ways of doing this. The first is emitting excrements in a liquid shape, saturated with sugar - the 'honey dew'. Its drops settle on leaves, fall onto the ground. The ants have adapted to licking straight from the aphids' bottoms. They milk them like cows. The guard them, they let them out to graze... but details of this will be discussed at another time.
   The second method: the excess of sugars is transformed in the organism into wax-like substances. The skin glands excrete them onto the surface of the insect's body, creating something like a protective armor or long waxy threads. As to who carries this upon themselves will be discussed in a little while. And now let us talk about those, who live in the 'cuckoo's spit'.
   On the stem of field carnation, red campion, willow - upon very many species of plants people have seen, of course, bundles of foam. Our folklore calls them the 'cuckoo's spit' or the 'cuckoo's tears'. Indeed, they are very similar to spit.
   A bundle of foam... We will carefully move it aside with a twig and we will see a small instance, somewhat green in color. It hurries to hide in foam once again...
   Being protected from dryness that is not tolerated by the cicadas' larvae, from the malignant gazes of birds and carnivorous insects, they live in this foam for their entire childhood. Sticking their proboscis into a stem or a leaf of the plant, they suck and suck its sap. The excess of the liquid, discarded by the organism, is excreted through the anal opening. The excretions have plenty of mycine - a substance often found in fungi, it increases the viscosity of a liquid. Using the respiratory openings at the end of its abdomen like an air pump, the froghoppers (or rather their larvae!) foam up this liquid.
   Still, the method of production of this foal is not fully known yet, although many experienced scientists have studied it.
   'The grasses weep', say the Germans when in the middle of summer the froghoppers develop their abilities fully... 'The weeping trees', say on Madagascar, when a multitude of the treehoppers' larvae will settle on one tree: rain literally drips from its branches day and night. Living-stone (this happened in Africa) once did think so: the rain started. But there was no rain, he only settled for a rest under tree where many treehoppers lived.
   One examiner had estimated: in 30 minutes 60 Madagascar treehoppers have filled a bottle completely with their foam!
   In 1853 the American scientist Isa Fitch caught, on the leaves of a grapevine, a small insect. It was an aphid, but an aphid of a species unknown to him. This insect was not yet introduced to the annals of science either. Dr. Fitch called the aphid discovered by him 'leaf-destroying pemfigus'. It should have been named thusly, but there are exceptions even from the rules of zoo-logical priority rules: for some reason the pemfigus began to be called not the first, legal name, but another, given to it in France - 'devastating phylloxera'. (Still, the phylloxera has two more scientific names that the zoologists gave it in England and Germany.)
   In 1863 the phylloxera suddenly appeared in England, where it was brought from USA together with the grape vine, then in France, next to Avignon, and immediately the famous grape vines of this country began to die one after another. The phylloxera, settling on the roots, drained them dry from all sap and the vine died. Quickly, the phylloxera destroyed 6 million hectares of grape vines in France. The wine-makers were forced to by grapes from other countries to fulfill their obligations before their clients. In 1900 the government of France counted the losses, caused by the phylloxera: the acts that accused the phylloxera a huge number was demonstrated - ten milliards of golden franks!
   Meanwhile, the terrible aphid continued its destructive trek through Europe, sowing everywhere despair and ruin. In 1869 it already reigned in the suburbs of Geneva. From there it moved down the Rheine and was soon destroying the grapes around Bonn. Then it visited Austria and clearly had settled there.
   In 1881 phylloxera was discovered under Sukhumi, then on Kuban, in Moldavia. A countrywide alarm was sounded. Teams of volunteers (high school and college students) went off to battle phylloxera. They saturated the soil with sulfuric acid. They poured water onto the roots to drown the aphids.
   Meanwhile, in America, a more effective weapon was invented. The entomologist Charles Reilly had noticed: thousands of American phylloxeras fall victims to small ticks. He suggested bringing these ticks to Europe and releasing them onto the local grapes. It was done. It was the first in history test of a biological method of fighting agricultural pests.
   Reilly also established that the American sorts of grapes are less affected by phylloxera than the European ones. Vine roots began to be brought from America and the local sorts were adhered to them via graft to breed, or, put otherwise, the European vine was grafted onto the American roots and, apparently, saved. The phylloxera is no longer as terrible as during the first years of its terrible march.
   That is true. However, a fully effective method of fighting it has not been found yet. The thing is that the vine graft is not cheap, and the harvests decrease after it as well. It is important to watch and prevent the phylloxera to settle in those vine areas where it is still absence, for example, in Central Asia and on Crimea.
   The phylloxera is just one out of approximately 3000 species of aphid known to science. Who, supposedly, doesn't know them? They scurry, slow and tiny, on leaves, branches of different trees, grasses (sometimes covering them completely!).
   Unseen, they do their harmful business underground as well: they suck the sap from the roots. Both here and in the greenery of the plants the ants scurry around them, gathering the honey dew.
   But not all of the aphids emit sweet droplets that attract the ants. Those, that live in the galls (bulges on plants), and those, whose bodies are deeply covered with waxy 'fluff' are sufficiently protected from the excessive drying-out. The skin of the honey aphids are tender and evaporate plenty of water. Consequently, the aphids are forced to constantly replenish its supplies - i.e. to suck and suck the plant sap in a larger amount than it is needed for sustenance. The undigested and unassimilated excesses are cast out by the aphids - and that is the honey dew.
   The development cycle of the aphids is quite complex. It exists in many versions, but in general it happens thusly: only wingless females emerge from the eggs that survived a winter. Without any male assistance, without fertilization (parthenogenesis) they give birth to the offspring that develop in the mother's body (it is called ovovivipariosity).
   The young aphids grow quickly and also breed parthenogenetically. There may be up to 17 such generations during a summer, in some of which winged aphids may be born (so far still only the females!) that migrate to another plant. There, winged and wingless generations alternate once more. The latter breed on the same plant where they were born, the former fly to another.
   There are the so-called single plant aphids, whose lives, or rather their development cycles pass on plants of a single species. But there are also those that live on different trees and grasses (even on the ferns). At that, some aphids need to change the species of plant hosts, and others do not. Shtefan Keler has estimated that the peach aphids feed on plants from 69 different families.
   But then autumn arrives, and the winged males are finally born in one of the generations. They find the females, fertilize them, and here the females lay eggs. The latter spend the winter, and in the next spring everything begins anew (admittedly, there are aphid species where the females survive the winter, but never the males).
   'The scale insects are the only group of terrestrial animals that arrive at a completely immobile way of life' (academic M.S. Gilyarov).
   Such are some of the females of the scale insect species: after sticking their long proboscis into a plant, they never withdrew it. Their only business is to suck sap and also to breed: their entire bodies, de-facto, is 'an egg-filled sack'. There are no eyes, legs, antennae. From above this 'sack' is covered with a waxy shield that resembles a scale. This strange insect can be easily taken to be an outgrowth, a partially fallen-off piece of bark, simply a piece of garbage stuck there.
   The scale insects of a special group, that an also crawl, are called ensign scales. Both in their and in the scale insects' cases, the males do not resemble the females at all: they are winged, look like small gnats or midges; they fly, but do not eat for the rest of their brief lives.
   The scale insects are pests of very many agricultural plants, especially the citrines. However, some are bred with positive results, like the cochineal insect. In Mexico, where the cochineal has originally lived, entire cactus plantations are grown specifically to feed millions of these scale insects. The expensive carmine color is produced from them. Later, such plantations were established in India, in Africa, on Madeira, on Malta, on Canary Islands. Even on the south of France and in Spain. But lately the chemical dyes have seriously lowered the value of carmine made from cochineal. Still, in the scientific labs, carmine is still highly valued as a dye of certain cellular structures. The same goes for the art. The scale insects of other species also provide carmine. Some of them also produce wax-like products, valuable polish and the famous shellac - the best wire isolator in electric and radio technology.
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