40 VINES 
This group is represented by all the caterpillars, 
larve and borers, whether they work on the 
fruits, stems, foliage, or roots of the plant or 
inside its tissues. The second class includes 
small, usually soft-bodied, insects which obtain 
their food by piercing the outer tissues and 
sucking juices from the interior of the plant. 
As examples of this group, we have the various 
scales, the leaf-hoppers, aphides, and such minute 
insects. 
From this consideration of the kinds of insects 
and the sorts of injury they produce, we can 
arrive directly at the general methods of pre- 
vention or extermination. For the first group 
of insects, we need simply provide some poisonous 
‘substance in such form that they will devour it. 
Since in many cases they eat the leaf tissues, 
this is easily accomplished by covering the leaf 
surface with a poison, ordinarily an arsenical 
compound. Of course, where the insects are 
few they can be removed by hand or killed on 
the plant, but if there is any liability of their 
appearance in great numbers, spraying is by far 
the simpler and more efficient measure. 
The sucking insect, in feeding, pierces the epi- 
dermis with its boring mouth-parts, or proboscis, 
and would therefore be unaffected by any poison 
