SOME NOTABLE INSTANCES OF THE DIS- 

 TRIBUTION OF INJURIOUS INSECTS 

 BY ARTIFICIAL MEANS 



,Ey FRED. V. THEOBALD, M.A. 



Vice-Principal of the Soutk-Eastem Agricultural College; President of the 



Association of Economic Biologists of Britain ; Foreign Member of 



the Association of Economic Entomologists, U.S.A. ; etc. 



One of the most noticeable phenomena amongst the insects 

 injurious to fruit, farm and garden crops, stores, man and his 

 domesticated animals, is the almost world-wide distribution ot 

 certain of these pests. That this distribution is not a natural 

 one we may safely infer from what we know of the general 

 range of insects. Some species spread over a very wide area 

 naturally, such as the Cotton Boll Worm {Heliothis obsoleta, 

 Fabricius), which is found in Europe, Africa, and America ; the 

 Army Worm {Leucania unipunda, Haworth), which is common 

 to both hemispheres ; and the Migratory Butterfly (Danais 

 archippus). Such instances are comparatively few in number. 

 In spite of these, we can say definitely that there is no insect 

 really cosmopolitan by nature. Just as with birds and other 

 animals, so with insects — each species has a definite area of 

 distribution. Many may increase this area by natural means, as 

 we see has taken place with the Mexican Boll Weevil {Antho- 

 \3tomus grandis, Boheman), and the Colorado Beetle {Doryphora 

 decemlineata, Say.), but only within certain limits. Hence when 

 we find some insects that attack plants, man, or animals almost 

 world-wide in distribution, we may be sure that their range is 

 due to some artificial cause or causes. On studying this subject 

 we can at once see how easy it is for certain pests to be carried 

 over the face of the earth by man's agency. 



\1 This distribution takes place by means of boats and trains 

 and all other ways of intercourse. The more rapid these means 

 of communication become, the more likely we are to see a 

 concomitant increase and spread of many injurious insects, 

 unless checked by stringent regulations. This dispersal has 



