I ^° THE STUDY OF INSECTS. 
(My'sus per'si-cae). The last three are almost invariably 
attended by ants. 
The Plant-lice of the genus Lachnus (Lach'nus) are 
usually found on the limbs of trees and shrubs. To this 
genus belong our largest Aphids, some of 
them measuring one-fourth inch in length. 
Figure 199 represents one of these enlarged. 
Fig. I w.-Lachnus. Some species of plant-lice live both on 
the roots and on the leaves of plants. One 
of these is the Grape Phylloxera, Phylloxera vastatrix (Phyl- 
lox-e'ra vas-ta'trix), which is the most important enemy of 
the grape. The presence of this insect is manifested by the 
vines in two ways: first, in the case of certain species of 
grapes, there appear upon the lower surface of the leaves 
fleshy swellings, which are more or less wrinkled and hairy; 
these are hollow galls, opening upon the upper surface of 
the leaf, and containing a wingless agamic plant-louse and 
her eggs; second, when the fibrous roots of a sickly vine are 
examined, we find, if the disease is due to this insect, that 
the minute fibres have become swollen and knotty; or, if 
the disease is far advanced, they may be entirely decayed. 
Upon these root-swellings we also find an agamic, wingless, 
egg-laying plant - louse, the author of the mischief. The 
insects found upon the roots differ slightly from those found 
within the galls, but their specific identity is now generally 
accepted. 
Owing to the great injury which this species has done to 
the vineyards of France, hundreds of memoirs have been 
published regarding it. But as yet no satisfactory means of 
destroying it has been discovered. The difficulty lies in the 
fact that the insecticide must be one that can penetrate the 
ground to the depth of three or four feet, reaching all the 
fibrous roots infested by the insect. It must be a substance 
that can be cheaply applied on a large scale, and it must 
also be something that will kill the insect without injury to 
