OUTLINES OF ENTOMOLOGY. 109 



Among the excessively injurious species of Aphides may be men- 

 tioned the Grape Phylloxera (P. vastatnx, Plan.) which has caused such 

 wholesale destruction of the vineyards in France and other European 

 countries, and prevents the cultivation of many choice varieties of grapes 

 in this country. This species occurs in two forms, one inhabiting 

 warty galls on the foliage, but the most destructive form occurring on 

 the roots, which it causes to decay. This species and its allies do not 

 produce the young alive, but always by means of eggs. Another root- 

 louse, belonging in another family, is the Woolly louse of the apple 

 ( Scliizoneura lanigera, Hausm.) This also sometimes appears above 

 ground on the trunk of the tree, and is one of the species that clothes 

 itself in a cottony or woolly excretion. . 



The Hop Aphis fPJiorodon humuttj often occasions great loss in 

 hop-yards, and Dr. Riley has made the intercBting discovery that in 

 autumn the winged migrant form resorts to plum trees and there pro- 

 duces the sexed individuals whose eggs hibernate on the plum, on the 

 leaves of which the first spring generations feed, becoming winged 

 early in summer and again returning to the hop-yards. The largest 

 species are found on the hickory and sycamore trees. These belong 

 to the genus Lachnus, and when thickly congregated on the trunks 

 and branches are a most repulsive sight. Some species, especially 

 those of the genus PempMgus, cause very singular galls on trees of the 

 poplar and willow family. As nearly all aphids are more or less injuri- 

 ous, it is out of the question to attempt here to give a list, even of 

 those that are serious pests. 



In the family Coccidep^ are grouped the Scale-insects or Bark- 

 lice, the Mealy-bugs and a few similar forms, which rival the members 

 of the preceding family in rapidity of increase, in injurious effect upon 

 the plants attacked and in the difficulty with which they are eradicated 

 or even kept in check. In these insects only the males undergo trans- 

 formation, protected by a small larval scale. They acquire wings, two 

 in number, very transparent and with only one or two veins. The 

 antennte are long, and, under the microscope, are seen to be many- 

 jointed and hairy or plumy. The mouth parts are undeveloped, and in 

 their place we find a second pair of eyes. The females never acquire 

 wings, and most of the species become fixed in one spot very shortly 

 after hatching, the long but extremely tine beak penetrating to the sap- 

 wood of the tree or shrub infested and slowly imbibing the sap required 

 to perfect the growth and development of the insect. Immediately 

 upon becoming fixed the surface of the body exudes a waxy substance 

 that very soon forms, together with the motled skins, a complete shell 

 or scale over the body. After being visited by the winged male, the 



