THE OUTLOOK FOR THE FUTURE 101 



As is also clear from the foregoing chapters, scarcely any 

 two insects may be dealt with most satisfactorily in exactly 

 the same way. This at once imposes upon the entomologist, 

 the task of discovering with as great detail as possible, the 

 exact life history and economic relations of a vast series of 

 insects, in order that energy may not be lost in the misappli- 

 cation of control measures. The last few years have seen a 

 great improvement in our knowledge of this kind, which has 

 already borne fruit in the rapidly increasing efficiency of 

 practical work. We can be sure that the future will see con- 

 tinuous improvement along these lines. 



The now widespread custom of spraying plants for the 

 destruction of insects has been made far more efficient 

 through careful attention to the physical and chemical prop- 

 erties of the materials and their physiological effects upon 

 specific insects. In the same way fumigation with poisonous 

 gases has been made more dependable. Various more or less 

 fundamentally new methods of combating various insects are 

 also continually coming into general use, usually through 

 some ingenious application of physical or chemical knowledge 

 to specific insects whose habits or physiological requirements 

 at some stage of their life-cycle lay them open to attack. 

 Thus mosquito larvae may be eliminated by oiling the surface 

 of the water in which they are developing, and housefly larvae 

 may be prevented from completing their growth in manure, 

 by storing it in specially constructed pits. In the same way 

 the chinch-bug, cotton-boll weevil, alfalfa weevil, certain 

 grasshoppers, cutworms, and a great variety of other pests 

 are commonly controlled in rather unique fashion. In fact, 

 the most efficient means of combating many insects are not 

 at all conventional, even to the entomologist. 



The biological method of reducing the numbers of injurious 

 insects offers at the present time, the most promising field in 

 which to speculate concerning the future development of 

 entomological practice. Much has already been said of the 

 principles and details concerned in the introduction and fur- 

 thering of diseases and of predatory and parasitic enemies in 



