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PHYLLOXERA (Gr. 4suXXov, leaf, and Er...

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Originally appearing in Volume V21, Page 547 of the 1911 Encyclopedia Britannica.
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PHYLLOXERA (Gr. 4suXXov, See also:leaf, and Erlpbs, dry)  , a genus of See also:insects belonging to the See also:family of Aphidae, or Plant-lice, in the Homopterous See also:section of the See also:order See also:Hemiptera . It is chiefly known from the causal relation of one of its See also:species to the most serious of See also:vine-diseases . The name was first given in 1834 to a plant-See also:louse which was observed to "dry up the leaves" of oaks in See also:Provence . About twenty-seven species are now known, all characterized by length not exceeding •o6 of an See also:inch, See also:flat wings, three articulations in the antennae, one or two articulations in the tarses, with digitules, but without cornicles on the See also:abdomen . The following full description of the only species which attacks the vine, the See also:Phylloxera vastatrix, or See also:grape-louse, is reprinted from the See also:article VINE in the 9th edition of this See also:encyclopaedia . " The symptoms of the disease, by means of which an infected spot may be readily recognized, are as follows: The vines are stunted and See also:bear few leaves, and those small ones . When the disease reaches an advanced See also:stage the leaves are discoloured, yellow or reddish, with their edges turned back, and withered . The grapes are arrested in their growth and their skin is wrinkled . If the roots are examined numerous fusiform swellings are found upon the smaller rootlets . These are at first yellowish in See also:colour and fleshy; but as they grow older they become.rotten and assume a See also:brown or See also:black colour . If the roots on which these swellings occur be examined with a See also:lens, a number of See also:minute insects of a yellowish-brown colour are observed ; these are the See also:root-forms (radi- cola) of Phylloxera (fig . I); they are about •8 mm. See also:long, of an See also:oval outline and with a swollen See also:body .

No distinction between See also:

head, See also:thorax and abdomen can be observed . The head bears small red eyes and a pair of three-jointed antennae, the first two See also:joints being See also:short and thick, the third more elongated, with the end cut off obliquely and Fm . I.—Root-inhabiting See also:Form slightly hollowed out . Under-(Radicola) of Phylloxera, with See also:pro- See also:neath, between the legs, lies the boscis inserted into See also:tissue of root rostrum, which reaches back to of vine. the abdomen . The See also:insect is fixed by this rostrum, which is inserted into the root of the vine for the purpose of sucking the See also:sap . The abdomen consists of seven segments, and these as well as the anterior segments bear four rows of small tubercles on their dorsal See also:surface . These root-dwelling insects are See also:females, which See also:lay parthenogenetic eggs . The insect is fixed by its See also:proboscis, but moves its abdomen about and See also:lays See also:thirty to See also:forty yellow eggs in small clusters . After the See also:lapse of six, eight or twelve days, according to the temperature, the larvae See also:hatch out of the eggs . These are See also:light yellow in colour and in See also:appearance resemble their See also:mother, but with relatively larger appendages . They move actively about for a few days and then, having selected a convenient See also:place on the See also:young roots, insert their proboscis and become stationary . They See also:moult five times, becoming with each See also:change of skin darker in colour; in about three See also:weeks they become adult and capable of laying parthenogenetic eggs .

In this way the insect increases with appalling rapidity: it has been calculated that a single mother which See also:

dies after laying her eggs in See also:March would have over 25,000,000 descendants by See also:October . If, however, the insect were content with this method of See also:reproduction the disease could be isolated by surrounding the infected patches with a deep ditch full of some such substance as See also:coal-See also:tar, which would prevent the insects spreading on to the roots of healthy vines . The fertility of the parthenogenetically produced insects would also diminish after a certain number of generations had been produced . As the summer wears on a second form of insect appears amongst the root-dwellers, though hatched from the same eggs as the form described above . These are the See also:nymphs, destined to acquire wings; their body is more slender in outline, and at first they bear well-marked tubercles . After several moults the rudiments of two pairs of wings appear, and then the insect creeps up to the surface of the See also:earth, and on to the vine . Here it undergoes its fifth and last moult, and appears as a wined See also:female, capable of reproducing parthenogenetically . The winged form has a slender body with distinct head (fig . 2) . The eyes are well See also:developed,with numerous facets; the antennae have three joints, the terminal one shaped like that of the root-dwellers . The wings are transparent, with few nervures, and are well adapted for See also:flight . The anterior pair reach far beyond the end of the abdomen; the posterior are narrower and not so long .

These winged forms are about I mm. long . They See also:

fly about from See also:July till October, living upon the sap of the vine, which is sucked up by the rostrum from the leaves or buds . They lay their parthenogenetically produced eggs in the angles of the See also:veins of the leaves, in the buds, or, if the See also:season is already far advanced, in the bark . In very See also:damp or See also:cold See also:weather the insect remains in the ground near the surface, and deposits its eggs there . The eggs are very few in number and of two sizes, small and large (fig . 3, b and c) . From the larger a female (fig . 4) is hatched in eight or ten days, and simultaneously, for the first See also:time in the See also:life-See also:history of the Phylloxera, a male (fig . 3) appears from the smaller See also:egg . Neither male nor female has wings; the rostrum is replaced by a functionless tubercle; and there is no alimentary See also:canal .

End of Article: PHYLLOXERA (Gr. 4suXXov, leaf, and Erlpbs, dry)
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