CHAPTER VIII 
How Insects SPREAD 
Tue spread of insects is brought about by a great variety of agencies, 
some of which are within human control, while others are not. It is 
the purpose of this chapter to point out a few of the former as well as 
the latter, and to emphasize the value of taking precautions to prevent 
the spread of noxious species. With many serious pests an ounce of 
prevention is worth a good many pounds of cure. 
Certainly the power of flight possessed by most insects is normally 
their principal means of dispersal to new feeding grounds. Unfor- 
tunately this is a matter usually quite beyond human control. Never- 
theless, as will be seen later, there are barriers even to powers of flight, 
and some of our most injurious pests, which are capable also of sustained 
flight, would never have reached this country at all, or the section where 
they are now a menace, had it not been for other means of dispersal 
entirely within the control of man. 
Strong winds, streams, ocean currents carrying débris or drift 
infested with insects, birds which are known occasionally to bear 
minute forms on their feet — all these are occasional means of the 
dispersal of insects and their introduction into new localities. 
But if we were to reckon up the hundred pests that are working 
greatest havoc with our farms and orchards to-day, we should find that 
at least half of them, if not three fifths, had been introduced, directly 
or indirectly, through the ageney of man himself. 
The ways in which this comes about are many. When shrubs or 
trees are imported from foreign countries, they are likely to be infested 
with pests new to this continent. The insect thus imported is apt to 
get a foothold and to develop into a pest of the first magnitude. It was 
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