570 



INSECTA. 



Pemphigus tcrebintlii by Derbes. Here the sexual animals are succeeded by 

 apterous asexual animals, which produce the galls, and the descendants of which 

 are the winged asexual generations which are dispersed and pass through the 

 winter. The reproduction of Chermes and Phylloxera is different, in that in 

 place of^the viviparous generations there is a special oviparous sexual form, which 

 also produces eggs capable of developing parthenogenetically. The apterous 

 females of the fir-tree lice pass the winter at the base of the young buds, 

 increase in size in spring in the same place, undergo several moults, and lay a 

 number of eggs. The young, when hatched, pierce the swollen pointed leaves 

 of the young shoots and produce galls. They develop later into winged females. 

 In Phylloxera quercus, besides the two generations, there is another genera- 

 tion, which appears in autumn and consists of very small movable males and 

 females (without suctorial proboscis or alimentary canal). These animals arise 

 from two kinds of eggs which are laid on the roots. The female, after copula- 

 tion, lays only a single egg. It is the same with the famous vine-lice (PA. 

 vastatrix), the larvae of which pass the winter on the roots of the vine 



(fig. 473). The principal enemies 

 of the Aphides are the larvae of 

 the Ichneumonidce (Aphidius}, 

 SyrpJiidce, Coccinellce and Heine- 

 robidce. 



a. Leaf -lice, s. st. ScJiizoneura 

 lanigera Hartg., on apple trees. 

 Lachnus pini L., L. jiifjlandis 

 L., L.fagi L., Aphis brassicce 

 L., A. rosce L. 



5. Bark-lice. Chermes dbictis 

 L., Ch. laricis Hartg., Phyl- 

 loxera quercus v. Heyd., on oak 

 leaves. Ph. vastatrix, vine- 

 lice, with winged and apterous 

 generations. 



Fam. Psyllidae (Psyllodes}, 

 leaf -fleas. Antennae long, with 

 ten joints. In the fully -developed 

 stage always winged. The hind 

 legs serve for springing. Their puncture often occasions deformities of flowers 

 and leaves. Psylla alni L., Livia juncoruin Latr. 



Sub-order 3. Homoptera-Cicadaria. Both pairs of wings are, as 

 a rule, membranous. Sometimes the front' pair is coriaceous, not 

 transparent and coloured. They lie, when at rest, obliquely on the 

 body. The head is relatively large, and often prolonged into pro- 

 cesses. The rostrum always arises low down, and apparently between 

 the front legs ; it has three joints. In many species the hind legs 

 are springing legs, with which the animal jumps before flight. The 

 females have an ovipositor, and often lay the eggs beneath the bark 

 and in the twigs of plants. The larvre of larger species may live 

 several years (fig. 474). 



FIG. 473. Phylloxera vastatrix. a, Wingless root-louse 

 seen from the back, b, from the ventral surface. 

 c. Winged form. 



