Saturday, September 24, 2011

Citrus leafminer: the nature learned to control it

For the small bird Chiffchaff its larvae are a food of Gods

The citrus leafminer is an insect of scientific name Phyllocnistis citrella that in its larvaria phase lives as parasitic under cuticle of the leaves and tender shoots of  the citrus trees of any species, feeding on the vegetal cells to which empty perforating its cytoplasmic membrane and sucking its liquid content. Exceptionally, in the absence of leaves, also it can parasitize the green fruits.

 Citrus leafminer in underside of a leaf of mandarin tree very affected in the middle of July of year 2006. The plague was at the algid moment of its expansion. It is appraised as the caterpillar goes with well-taken care of of not breaking cuticle that serves to it as protection. It advances taking off it of the cells and after perforating the cellular membrane it absorbs all their content

This parasite is original of Southeast Asia, where it has coexisted with its guest, the citruses, during million years. Due to the height of the commerce and interchange of plants and animals at world-wide level at the end of century XX it began to expand towards Australia, Near East and Africa, arriving at the south of the Iberian Peninsula in August of 1993, being detected for the first time in Malaga. In the following months it went extending towards all the coastal subtropical and Mediterranean climate regions from the Mediterranean river basin where citruses are cultivated and in 1994 it arrived at the Island of Majorca. The Soller Valley, famous by its great plantations of excellent citruses, few months one became a very harmful plague, preventing the trees to renew its leaves when destroying the new buds.

Detail of the caterpillar of the citrus leafminer who is leaving behind himself a thread of defecations. In the other half of the leaf there is another leafminer.

 When the caterpillar reaches the adequate size after happening through four phases of growth, it realises the last dumb and it is transformed into pupa, whose mouth in the form of tube secretes threads of soothes to generally form the pupal camera closely together of the edge of the leaf. Finished their work of weaver, the threads of soothe are dried and dissuaded, which causes that the leaf bends on the pupal camera, thus being protected and outside the view of its predators. Days later the winged adult leaves and after the fertilization the female looks for tender buds and puts its transparent eggs on the future leaves that still are forming.

 Already empty pupal camera in September after the exit of the adult. The edge of the leaf is seen well that bent inside towards protecting the nymph while it was being metamorphosed.

The leaves very affected are become deformed, the eaten part is dried and the tree finishes coming off itself them. When the attack is very intense the citrus is not able to bring forth new leaves and must survive with old, that is to say, those that already it had before the beginning of the plague, which they hold without falling more time of the normal one so that the tree does not die drowned for want of leaves that are its lungs and their food factory through the energy of the sun. Four years after the beginning of the plague many trees practically were defoliated, realising the photosynthesis through the green crust of their more tender stems. They were condemned to a safe death in two or three years.

The fruit and vegetable agriculturists of Soller were scared before the virulence of the plague and looked for remedies in the Cooperative. Nobody knew nothing of this new disease of the citruses. At the outset they tried with classic insecticides, but they did not work, soon arrived from the USA the supposed specific pesticide for this parasite at a prohibitive price for the battered economy of subsistence of the majority of agriculturists. Thousands of former pesetas were spent without no result. The frustration and the sensation of impotence were very great, until the point that many market gardeners occurred by won and accepted to lose for always their magnificent orange trees, lemon trees, mandarin trees and grapefruits. They let then fumigate its citruses with useless pesticides with the conviction that in fact everything had been a assembly to remove the money to them, including the appearance and inexplicable sudden expansion of the plague, as if some multinational was behind everything. 

Tender leaves of the citrus Severina buxifolia attacked by the citrus leafminer. In my garden I could verify as the leafminer did not have any special preference by a determined species of citrus, it the same attacked but them all whenever they tried to bring forth new leaves. Aside from the orange trees, lemon trees, mandarin trees, clementin trees, grapefruits and the Severina of the photo, also affect to Fortunella margarita or Kumquat, the pamplemusa, the chironja of Puerto Rico, the citron " Buddha´s hand" , the Atalantia citroides, the citrangequat, the limequat and the calamondin.

 Leaves of the Australian citrus Microcitrus australasica half dry after partially being eaten by the leafminer of the citruses.

And then came the moment of master acting of nature. From the year 2000, about 6 years after its arrival to the island, the plague began to diminish inexplicably, every spring were less affected buds, many leaves managed to grow whole and the citruses little by little were covered again with splendid treetops of intensely green healthy leaves. What was happening? 

The scientists of the University of the Balearic Islands along with the technicians of the Council of Agriculture studied the strange phenomenon and discovered that a few native insects predators of other insects, as wasps Dacnusa sibirica and Diglyphus isaea, had proliferated exaggeratedly and they had specialized in feeding on the citrus leafminer. Without needing most expensive pesticides of the multinationals, the wisdom of the nature had managed to reduce to tolerable limits the plague of the leafminer. I was glad to much when reading this news and also by to have resisted the temptation to buy insecticides to multinationals. In my garden nonuse pesticides nor chemical fertilizers. I save much money and much work, the earth is very healthy flood of earthworms and I can directly be eaten the fruit of my trees to bites without needing peeling it nor washing it to clear no poison. The majority of " plagues" of my trees perfectly they are controlled by the own nature. 

A day about 7 years ago taking a walk by my garden a tiny small bird, Phylloscopus collybita, drew attention to me, that jumped of small branch in small branch on an old lemon tree and watched underneath each leaf. Of as much as soon as it found a small worm, it squashed a little with its smallest tip of insectivore and swallowed it as if outside delicious food. The bird overflowed joy and realised a species of dance with small jumps and movements of the tail whenever a worm swallowed. I was observing it during a good short while and it did not seem to bother my presence, so engrossed was with its big spread. When it was sated of worms went flying until the drinking trough of geeses, drank several times and it disappeared. Suspecting that it had been fed on leafminer larvae, I look under the leaves where the bird had been and indeed all cuticle had broken and the larva had disappeared.

After 17 years of the beginning of the plague today I have wanted to verify the state of the new buds of this year of the orange trees, lemon trees and mandarin trees and I have only been able to find two affected leaves. The intelligent action of the nature has been spectacular, a full success.

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