1921] The Age of Insects 39 



These are but a few of the many illustrations that I might have 

 drawn from the great field of appHed entomology but they will perhaps 

 serve to illustrate its many phases. ; 



Insect Friends. 



Entomologists lay so much stress upon the damage caused by in- 

 sects that it is small wonder that the public is inclined to look upon 

 insects as pests and nothing else. It was that eminent British Ento- 

 mologist, Sir John Lubbock, I believe, who brought the opposite point 

 of view to our attention forcibly by reminding us that he could make 

 the world a place unfit for human habitation in less than a year's time 

 if he had the power to remove certain insects from the world. Which 

 is simply another way of saying that while we suffer much from the 

 attacks of injurious insects we owe much to insects which are our 

 friends and help to keep injurious insects in control. 



Entomologists are having these matters forced upon their atten- 

 tion but apparently the general public misses the significance of the 

 outbreaks of certain species of insects. The army worm is a case in 

 point. Normally this insect is present every year but not in sufficient 

 numbers to cause any appreciable loss to the farmer. Occasionally, 

 however, the army worm becomes locally or generally abundant and 

 causes wide spread destruction and alarm. Even a better illustration 

 is offered by the soy bean worm. A year or two ago this insect 

 threatened the destruction of the soy bean crop of this and adjoining 

 states causing hundreds of thousands of dollar's worth of damage. 

 Yet this insect is not even mentioned in standard textbooks of ento- 

 mology and had never been a serious pest before. Why these sudden 

 outbreaks of insect pests? The reply is that these destructive out- 

 breaks represent what happens when the control exercised by their 

 enemies is for any reason released. In other words it represents the 

 condition that would prevail but for our insect friends. 



"The following analysis of a typical outbreak of the armj^ worm 

 will show what usually happens. As is usual during such outbreaks, 

 large numbers of Tachina flies were to be found in the fields laying 

 eggs on the worms. With the intention of making a more careful 

 study of these parasites 491 larvae were brought back and placed in 

 cages. The following data gleaned from the records of these cages are 

 presented as being of some interest. Of the 491 larvae, 442 were in- 

 fested with the eggs of the dipterous parasite, leaving only 49 larvae. 



