6 
INJURY FROM SUCKING INSECTS. 
The sucking insects are those which injure plants by the gradual 
extraction of the juices, either from the bark, leaves, or fruit, and include 
the plant-bugs, plant-lice, scale insects, thrips, and plant feeding mites. 
These insects possess, instead of biting jaws, sucking beaks or bristles, 
which are thrust down through the outer layers of the bark or leaves 
into the soft, succulent tissues beneath and used to extract the plant 
juices, with a resulting injury not so noticeable as in the first group, 
but not less serious. 
For this class of insects the application of poisons, which penetrate 
little, if at all, into the plant cells, is of trifling value, and it is neces- 
sary to use substances which will act externally on the bodies of these 
insects, either as a caustic or to smother or stifle them by closing their 
breathing pores, or to fill the air about them with poisonous fumes. Of 
value also as repellants are various deterrent or obnoxious substances. 
Wherever it is not desirable to use poisons for biting insects, some of 
the means just enumerated will often be available. 
GROUPS SUBJECT TO SPECIAL TREATMENT. 
The general grouping outlined above relates to the species which 
live and feed upon the exterior of plants for some portions or all of 
their lives, and includes the great majority of the injurious species. 
Certain insects, however, owing to peculiarities of habit, inaccessibility, 
or other causes, require special methods of treatment. Of these, two 
groups properly come within the scope of this bulletin: (1) Those 
working beneath the soil, or subterranean insects, such as the white 
grubs, root-maggots, root-lice, etc., and (2) insects affecting stored 
products, as various grain and flour pests. 
Three other groups, which include species requiring very diverse 
methods of treatment, and therefore not coming within the limits of 
this bulletin, are (1) the internal feeders, such as wood, bark, and stem 
borers, leaf-miners, gall insects, and species living within fruits; (2) 
household pests, and (3) animal parasites. 
The classification of insects outlined above, based on mode of nour- 
ishment and indicating groups amenable to similar remedial treatment, 
simply stated, is as follows: 
I. External feeders: 
(a) Biting insects. 
(b) Sucking insects. 
Il. Internal feeders. 
Ill. Subterranean insects. 
IV. Insects affecting stored products. 
V. Household,pests. 
VI. Animal parasites. 
