THE CANADIAN ENTuMOLOGIST. 80 



when the shipments reacli their journey's end. This is doubtless the chief 

 means of the distribution of the codling moth which has been so destruc- 

 tive this summer. The larvfe of these, being inside the shipped apples or 

 pears, work their way out from cocoons in the corners or crevices of the 

 boxes or barrels, and, when the fruit has been distributed, these are over- 

 looked and so have a chance to come to maturity, and to emerge in due 

 time and establish themselves in the neighbouring orchards. 



Every farmer knows how easy it is to ship pea weevils in seed peas, 

 and so will readily understand that all beetles or moths that infest grain 

 of any sort, flour or meal could easily be distributed in a similar way. 

 That this is the chief means of the wide spreading of such insects there 

 is no doubt. 



In connection with commerce, we might also mention, in passing, 

 that it is very probable that great international exhibitions, such as those 

 held in Chicago and Paris, are important factors in the spread of insects, 

 but that any very serious pest has been introduced in this way does not 

 seem to have been proved. Provincial and other exhibitions or fairs also 

 act as distributors, but on a much more limited scale. 



Sufficient has now been said to show how very important commerce 

 is as a means of insect distribution. There still remain a few factors that 

 require to be taken into consideration. 



If we think over the question we shall find it but natural that in a 

 new country like Canada or the United States, where much land is being 

 brought under cultivation for the first time each year, insect spread should 

 be more noticeable than in older countries, where there are no virgin 

 lands to break up. By this opening up of new districts the balance be- 

 tween insect and plant life is broken. The plants that the insects lived 

 upon are destroyed, and, consequently, the latter are forced to adapt 

 themselves, wherever possible, to the new sources of food provided by the 

 farmer's crops, usually, of course, attacking plants of the same order as 

 those which they had been accustomed to feed upon. Thus a once harm- 

 less insect has gradually, or even suddenly in a few cases, changed into an 

 injurious one. This is what happened in the case of the Colorado beetle. 



It has, moreover, been found that foreign insects brought into North 

 America become, in most cases, more destructive, and increase more 

 rapidly, than in their native land. There are probably several reasons for 

 this. In the first place, the climate of much of this continent is very 

 favourable to insects. In the second place, our plants, when first attacked 



