306 THE PRACTICAL APPLICATION OF ECOLOGY 



ground afford an inexhaustible supply upon which the winged 

 swarms make relatively little impression. There appears to be 

 no doubt that migration is intimately connected with the 

 development of the genital products, as happens also in the 

 case of the nuptial flights of termites and of ants. With locusts 

 the flight acquires a regularity and duration of such a character 

 that it goes on so long as physiological causes impel it. It may 

 terminate or only be interrupted owing to unfavourable environ- 

 mental conditions, but physiological causes such as the exhaustion 

 of the fat-body by oxidation, and the rise of body temperature, 

 resulting from flight, accelerating the maturity of the sexual 

 products, appear to be of greater importance. It is further 

 noteworthy that the available evidence indicates that the 

 emigration is not concerned with the quest for suitable new 

 areas for egg-laying. The settling of swarms in places totally 

 unsuited either for feeding or oviposition has often been recorded 

 and is totally opposed to this, at one time, prevalent belief. 



There is obviously much that remains obscure in the phase 

 theory, and the various factors involved require deep and 

 searching investigation with respect to different species of locusts. 

 The theory, although an established fact, is still very largely 

 hypothetical as regards fundamental causes. It lends, however, 

 a new and essentially ecological interpretation of locust outbreaks. 

 By directing research along a defined course, it will co-ordinate 

 investigation, hitherto largely prosecuted blindly in the hope 

 of eventually alighting upon some solution of the problems 

 concerned. It opens up the possibility that mass transformation 

 of locusts into the gregarious phase may be foretold, while 

 discovery of the locations of the favoured breeding grounds may 

 lead to the destruction, by aeroplane dusting, of immense numbers 

 of potentially harmful individuals. Further, ecological study 

 opens up the possibility of altering the character of such breeding 

 grounds, either by cultivation or other means, and thereby 

 rendering them less potent sources of the invasion of other lands. 



The Species of True Locusts. The species of true migratory 

 locusts are relatively few in number. In the light of the phase 

 theory their number has been about halved, since forms hitherto 



