AC AD AS— PLANT-LICE 201 



rare males do not appear till the autumn, and are mostly much smaller than the 

 females, at times attaining only a fifth of their size. After their appearance the 

 females deposit the eggs, which remain in the bark through the winter, from 

 which the young emerge in the spring. These latter cast their skins several times, 

 and grow up, either depositing eggs, or bringing forth live young, and that to the 

 tenth generation and more without males. The earlier generations invariably 

 consist of wingless insects, and not till the end of summer are there any capable 

 of flying and settling on other plants. In consequence of their rapid increase, 

 these insects often become highly injurious. In spring they collect round the 

 opening buds, later on attacking the young shoots, which they frequently cover in 

 such numbers that the leaves curl and wither. Many kinds by their bite cause 

 plants to twist, and turn up the leaves and stalks, and thereby bring about other 

 changes, perhaps for the protection of the young. Although no indigenous 

 tree is entirely free from them, and many, such as willows, harbour from eight 

 to ten species, these pests exercise but little influence on forest-trees. They are 

 much more harmful to fruit-trees, and also to herbaceous plants, peas, beans, 

 and corn, especially where their propagation is assisted by dry oppressive air or by 

 manuring, which forces the young shoots too fast. In hothouses defective 

 ventilation similarly assists in their increase. 



Among those living on rose-bushes, is the rose-aphis (Aphis rosce), which is 

 green on green shoots, though red on red ones, the males being distinguished by a 

 double row of black dots on each side. It migrates from roses to the scabious and 

 thistle, and frequently harbours the pupae of an ichneumon-fly. On the under side 

 of the leaves of plum-trees A. pruni is often found in such numbers that the 

 leaves, overspread with honey-dew, are blackish ; and trees so overrun bear no fruit. 

 This insect is light green, powdered with white all over, and, if winged, has three 

 green longitudinal stripes on the abdomen. Beneath the bark of apple-trees, 

 and there only, flourishes the blood-aphis (Schizoneura lanigera), which leaves a 

 blood-red spot when crushed. The insect is yellow, covered all over with whitish 

 flakes, and is the most injurious of all species: it is found in the injured parts of 

 young trees, as well as in the cankers and fractures of old trees. The females 

 appearing late in the autumn deposit their eggs at the foot of the apple - tree 

 stems, whence the young ascend the trunk and damage it, by preventing the 

 healing of wounds due to pruning and accident, so that the trees die oft* in 

 consequence. On young fir - shoots are often found plug-shaped galls, in which 

 are the larvae of Chermes abietis. This species is reddish brown powdered with 

 white, lighter on the antennae and legs, and white-winged. In hollows at the roots 

 of firs, whence they come to the surface over-night, live the larvae of Rhizobius 

 pini, which are brown, with a white woolly covering. The larva returns to its 

 haunt in the morning, and often leaves its skin as meal-dew on the leaves. 



In another family, the Coccidce, there is a great difference between 

 the males and females. The males have two or four wings with only 

 a double vein, and are without a beak, and they undergo complete metamorphosis, 

 occasionally even sheltering in a cocoon ; whereas the females are without wings, 

 but have beaks, and undergo no metamorphosis. The beak serves to attach them 

 by suction to the bark, leaves, and other parts of the plant, so that they can deposit 



