6 
SUCKING INSECTS, 
Under the second head is grouped the injury due to the gradual 
extraction or absorption of the juices of the plant, either from the 
bark, leaves, or fruit by such sucking insects as. plant-bugs, plant-lice, 
scale-insects, Thrips, and also plant feeding mites, as the red spider. 
These insects possess, instead of biting jaws, sucking beaks or bristles, 
which are thrust down through the outer lavers 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. 
It is evident that for this class of injury the application of external 
poisons, which penetrate little, if at all, into the plant cells, will be of 
trifling value, and, in fact, for all these insects it is necessary to use sub- 
stances which will act externally on the bodies of the 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 are deterrent or obnoxious substances which repel the insects. 
In the cases also, referred to above, where it is not desirable to use 
poisons for the biting insects, the use of caustic or smothering washes 
is always advisable. 
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, ete., and (2) insects affecting stored 
products, as various grain and flour pests. 
Three other groups, which inelude 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 inseets, and species living within fruits; (2) 
household pests, and (3) animal parasites. 
In brief, the classification of insects outlined above, based on mode 
of nourishment and indicating groups amenable to similar remedial 
treatment, simply stated, is as follows: 
I. External feeders: 
(a) Biting insects. 
(b) Sucking insects. 
lI. Internal feeders. 
IL]. Subterranean insects. 
IV. Insects atfeeting stored products. 
VY. Household pests. 
VI, Animal parasites, 


