THE CANADIAN KNTOMOhOGIST. 85 



PRACTICAL AND POPULAR ENTOMOLOGY.— NO. 19. 

 How Insects are Distributed.' 



BY L. CAESAR, ONTARIO AGRICULTURAL COLLECiE, GUELPH. 



We are all aware that there are many insects in our country to-day 

 that were unknown here a few years ago. Even middle-aged men and 

 women of our farming community can well remember the time when there 

 were no Colorado beetles (potato bugs), no cabbage butterflies, no pea 

 weevils, and no San Jose' Scale to worry their minds. The fact is that 

 the majority of our worst insect pests are not native, but have been intro- 

 duced either from Europe or the United States, many of the latter coming 

 originally from European or other foreign sources. The following very 

 incomplete list of imported insects will make this point clear : Codling 

 moth, cabbage butterfly, currant worm, Hessian fly, wheat midge, clover 

 weevil, both kinds of asparagus beetles, Colorado beetle, horn fly, Buffalo 

 carpet beetle, house cockroach, most of our plant lice or aphides, white fly, 

 oyster-shell aifd San Jose' scales, and most of our granary pests and meal 

 worms, as they are commonly called. 



Of these injurious insects more than three-quarters have come to us 

 from Europe through the United States, though one of the worst, the San 

 Jose Scale, has been traced back to China. But even in the case of the 

 European importations, it fs probable that many of them had their 

 original home in the still earlier civilized portion of the continents of Asia 

 and Africa, whence they spread to Europe and now have come to us. 



How, then, has this world-wide distribution of insects been brought 

 about? To answer this fully is impossible, but some of the chief means 

 have been observed. There is no doubt that trans-oceanic insects have 

 been brought to us through the channel of commerce. On nursery 

 stock, especially before the days of compulsory fumigation, were carried 

 from country to country, scale insects. Aphides (both in~ the egg and in 

 later stages)^ borers and other orchard insects or their eggs. On green- 

 house plants were carried the particular insects that trouble the floricul- 

 turist, such as the red spider, mealy bugs, different kinds of Aphides, 

 thrips, etc. In grain and various kinds of seeds and nuts, and in flour or 

 meal, came the various granary and meal pest^. On cattle, swine and 

 sheep were brought the different kinds of flies, lice and ticks that infest 

 these animals. In packed fruit were brought the eggs, larvae, cocoons or 

 adults of many of the fruit-destroying or other pests that frequent the 



March, 1907. 



