67 
2. Barriers to progress may be opposed to the spread of the 
injurious species from place to place, or directed to preventing the 
individual insect from gaining access to its food or place of ovipo- 
sition. 
3. The capture of insects may be accomplished either directly, 
by hand, or indirectly, by lures and traps; and their destruction 
when captured may, of course, be effected in a great variety of 
ways, differing according to circumstances and convenience. 
4. Topical applications may be either destructive or repellant, 
intended to kill the insect or to drive it away. ‘The destructive 
agencies are either in the nature of internal or external poisons,— 
killing by contact or by their action after being taken into the 
alimentary canal. The internal poisons can rarely be used except 
for the orders previded with masticatory mouths, which therefore 
bite and chew their food before swallowing it; and they are not 
usually available against such insects as take their food by suction 
through a beak or proboscis. 
Under the above system of classification of remedial and preven- 
tive measures, we May now arrange, for convenient reference, the 
modes of resistance to the attacks of strawberry insects which have 
thus far been devised. 
1. Moprs or CuLTuRE. 
1 a. Grass lands should sometimes be cultivated for two or three 
years in some hoed crop, to expel the root-eating insects which 
devour not only the roots of grass, but also those of strawberries. 
pa measure is especially recommended against the various white 
grubs. 
1b. In the vicinity of towns where gas is manufactured, the 
lime used in purifying the gas becomes saturated with sulphur, and 
accumulates as a waste product, known as gas lime. In a fresh 
state this is destructive to both vegetable and animal life, but on 
exposure to the air it is eventually converted chiefly into the car- 
bonate and sulphate of lime, both valuable fertilizers for many soils. 
These facts suggest the following procedure to free the soil from 
noxious insects, preparatory to a change of crops. Ilirst treat the 
surface to a dressing of fresh gas lime late in summer or carly in 
autumn, and plow this under at once, and then apply a second 
dressing of the lime to the plowed surface. As the rain washes 
this into the soil, it will destroy the earth-inhabiting insects both 
in thas part of the soil turned over and for some distance beneath. 
The details of this procedure are still subjects for experiment, and 
neither the amount to be used, nor the length of time it 1s neces- 
sary to leave the fresh lime in the ground before planting, have as 
yet been definitely ascertained. The value of this application as a 
pane will also vary according to the character and history of 
the soil. 
