56 INSECTS AND HUMAN WELFARE 



does not occur on the egg ])lant or potato, although it is the 

 common enemy of tobacco known as the bud- worm, and is 

 moreover a very important enemy of both corn and cotton, 

 two totally unrelated plants. On these latter it has been 

 called the corn ear-worm and the cotton boll-worm, but it is 

 identical and feeds on these several plants without much 

 apparent choice. 



Insects of this type point out clearly the fallacy of any 

 statement that related plants always have the same or re- 

 lated insect pests. That they quite generally have the same 

 enemies or nearly related ones with similar life history and 

 habits is, however, ordinarily quite true. 



How can this damage be abated or lessened is the natural 

 inquiry from the non-academic mind. We have seen that a 

 return to natural conditions would speedily reduce insect 

 injury and bring into play the forces of nature which would 

 maintain a more or less stable condition. Such a return 

 would not take place, however, if human influence were 

 simply removed; it is true that a stable condition would re- 

 sult, but it would be very different from that which existed 

 in the original flora and fauna. Indeed human ingenuity 

 could not again make things as they were, even if it were de- 

 sired to do so at the cost of discarding all agricultural prog- 

 ress. It is, however, possible by an additional disturbance 

 to approach in some respects to a natural biological associa- 

 tion without disturbing agriculture in the least degree. 



This partial return to the native environment can be 

 achieved to some extent by the introduction of parasitic in- 

 sects and other organisms, and this biological method of 

 combating imported insect pests has proved itself of value 

 in many cases. Up to the present time the importation, colo- 

 nization and distribution of such enemies has been accom- 

 plished in this country with the parasites of the gipsy moth 

 and to a less degree with those of certain other insect pests. 

 The method gives great future promise, but there are many 

 technical difficulties to be overcome. Its great advantage 

 lies in the fact that it insures permanent relief once it has 



