110 



INSECTS INJURIOUS TO GRAPE VINES. 



every remedy required to be tested on a fair and sufficient scale, and more 

 than once. All this trouble and expense, however, has as yet been fruitless ; 

 no remedy has been found. 



" In the earlier part of its cycle for it has a cycle, as we shall presently explain 

 it appears under two distinct forms, both wingless, which differ, not mater- 

 ially, but sufficiently from each other, the one having tubercles on the back, 

 and the other being almost without them. The former is found exclusively 

 upon the roots, the latter on the leaves ; but they have been traced going from 

 oi' e to the other. They are so small that they can hardly be detected with the 

 naked eye, but under a lens are seen to be of a fleshy texture, and light yellowish 

 brown in colour. Under this form both larvae and females are found. 



"If we examine the root 

 and try to trace the insect, 

 its course of life seems to be 

 this : It fixes itself, like 

 the Coccidce, to the root by 

 inserting its sucker or beak 

 into the bark of the root, 

 and when once fixed it 

 remains there for the rest 

 of its life. While so fixed 

 she lays around her, in little 

 groups, a quantity of ellipti- 

 cal eggs, which are at first a 

 fine sulphur-yellow colour, 

 but afterwards take by 

 degrees a smoky-gray or 

 blackish hue, a point in 

 which it corresponds rather 

 with the Aphides than the 

 Coccidce. After about eight 

 days a larva comes out of 

 the egg, which resembles, 

 except in size, the mother 

 that laid it, but it is of a 

 greenish yellow colour. The 

 larva thus hatched is at first 

 restless and agile, but at the 



d e 



Fig. 46. PHYLLOXERA VASTATRIX, leaf form : 

 a, section of leaf gall ; b, c, larvas newly hatched ; 

 d, upper view ; e, under view; /, side view of the 

 mother gall louse. All the figures, except a, 

 greatly enlarged. 



end of three or four days it has chosen its place and fixes itself by its sucker and 

 remains on the spot. It undergoes three moults, separated from each other by 

 from three to five days. After about twenty days the female larva becomes adu]t 

 and lays about thirty eggs ; the number of 

 generations in a year is estimated at eight, 

 which gives a posterity of from twenty- 

 five millions to thirty millions during a 

 season for fach individual. That is the 

 course of life of the great majority of 

 Phylloxera, but a few undergo five moults 

 instead of three, which brings them to the 

 superior state of insects endowed with 

 flight. In this stage they have four wings, 

 of which the anterior pair are transparent, 

 but darkened as if with smoke at the end. 

 The winged female lays its eggs in the 

 down of the young leaves and buds, and Fig. 47. PHYLLOXERA VASTA- 

 the eggs that it lays are larger and in fewer THIX, wingless female ; a, upper 

 number than those of the apterous females surface ; b, under surface. Greatly 

 on the roots, and they are of two sizes, of enlarged. 



