36 THE REPORT OF THE No. 33 



as to which enemy is the most promising and which in the end may be the most 

 effective. What is needed in this respect is facts and these can only be secured 

 by experimentation, the methodical collection and proper weighing of field data 

 and good judgment in drawing conclusions. 



The policy has been followed of securing all natural enemies of the gipsy 

 moth that gave any promise of becoming successfully established in America, in 

 the hope that as great or possibly greater measure of control by natural enemies 

 can be secured than exists in the native home of the insect. 



Few will doubt the wisdom of this policy, and probably fewer would adopt 

 a different plan were they responsible for the management of the work. 



I have dwelt at some length on the problem of natural enemies as applied to 

 the gipsy moth work. Time has made it impossible to mention details. The 

 project is the largest of its kind that has ever been attempted, and the data that 

 has been obtained and the results thus far secured should be useful to all inter- 

 ested in the control of insects by natural means. The work thus far indicates 

 that enormous progress has been made along this line and demonstrates it to be 

 one of the promising and valuable fields that should be thoroughly investigated 

 by economic entomologists. 



A brief summary may be helpful: 



1. Natural enemies are a powerful means of controlling most insects. 



2. Insects imported from foreign lands leave their natural enemies behind 

 and under favourable conditions are capable of more rapid increase and destruc- 

 tiveness than is usual in their native environment. 



3. If the major factors favouring control of an insect are to be utilized it is 

 necessary to make a careful study of the fluctuations of the pest, and the damage 

 done in its native home, preferably before, rather than after, it becomes located 

 in a new country. 



4. Until such work has been thoroughly done so that the prime factors 

 which bring about the natural control of the insect in its native home have been 

 thoroughly determined, it is desirable to secure and colonize all neutral enemies 

 that give promise of assisting in the problem of control. 



5. While theoretical considerations may sometimes be of value, definite 

 facts are needed as a basis for securing the greatest benefit by natural enemies. 



THE ONION MAGGOT IN ALBERTA 



H. E. Gray, Entomological Branch, Dominion Department of 



Agriculture 



Previous to the season of 1922, the Onion Maggot, Hylemyia antiqua Meig., 

 had been reported from only a few localities in Alberta, including Edmonton, 

 Red Deer and Lacomb. The infestation in 1922 was general over the area south 

 of Calgary and somewhat localized to the north. The sudden increase over such 

 a large area caused considerable consternation among the gardeners, and the 

 heavy infestation late in the season of 1922 indicated that more trouble could be 

 expected in 1923. With these facts in mind, the study of the onion maggot was 

 made the major garden-insect problem at the Lethbridge Entomological Labor- 

 atory during the season of 1923. 



This season will long be remembered in Alberta not only as a wet year, but 

 as the year which broke a five years' drought. The rainfall for May, June and 

 July was well over the twenty-year average for these months, and some of the 



