78 THE CANADIAN ENTOMOLOGIST 



which may, indeed, never be solved. We know that itvS breeding 

 grounds once extended over a very wide area, much of this having 

 been classed as permanent by Riley and others who investigated the 

 plague at that time. At present, however, the insect seems to have 

 vanished completely. Indeed, there are some who would place it 

 with the Passenger Pigeon as an object of the past. It seems 

 almost incomprehensible, however, that such can be the case. 

 More probably the real permanent breeding grounds are more 

 restricted than was supposed, and the locust will yet be located 

 either by the discovery of its real haunts or by a new invasion fol- 

 lowing favourable weather conditions for breeding purposes. This, 

 however, is beside the question. What I wanted to point out was 

 that the Rocky Mountain Locust always invaded Western Canada 

 during a dry season, arriving in swarms from elsewhere in July or 

 August. As this was the time of oviposition. eggs were soon de- 

 posited in vast numbers, and, as a result, crops naturally suffered 

 much more the following year than they did on the insects' first ap- 

 pearance. While the locusts were able to breed for a season or so 

 in the invaded territory they seldom remained long. Frequently 

 an excess of moisture to what they had been accustomed to pro- 

 duced sickness from which many died, while others taking advan- 

 tage of sunny days and favourable breezes drifted to parts un- 

 known. 



In other words, dry weather had enabled them to overstep their 

 usual breeding grounds, only, however, to be driven out or killed 

 by a return to normal climatical conditions. The same dryness 

 which induced an invasion of Rocky Mountain locusts was also 

 instrumental in increasing the indigenous species of Orthoptera, so 

 that such kinds as the Lesser Migratory Locust {M. atlanis) be- 

 came almost as destructive as its close relative mentioned above, 

 while many other species were sufficiently numerous to aid material- 

 ly in the work of destruction. We have another example of an 

 insect's control by conditions of humidity alone in the Western 

 Wheat-stem Sawfly (Cephus sp.). In this instance a lack of 

 precipitation causes a dearth of the flowering stems of grasses in 

 which the larval life is passed, resulting in a decrease of the species 

 in proportion to prevalence of suitable grass stems for breeding 

 purposes. This, of course, relates to natural conditions before 



