CHAPTER VIII 

 How Insects Spread 



The 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 omice 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 debris 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 agency of man himself. 



The wa^^s 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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