476 



fixed hibernation quarters. He considers that the general opinion 

 to the contrary is based upon theory without any well founded basis 

 and upon an artificial classification of the areas infested more or less 

 permanently or simply temporarily. It seems useless to attempt 

 to trace the cause of locust invasions to meteorological changes or 

 other conditions ; migration is apparently instinctive, and if con- 

 ditions are favourable, there is no Hmit to it. In 1919 the 

 presence of locusts in the flying stage was recorded on 28th 

 July in five provinces and many districts ; these swarms, though 

 decimated by natural enemies, had evidently passed the entire winter 

 in the Central Argentine zone, simply passing from one locahty to 

 another, taking short flights in irregular directions when conditions 

 were favourable. If there were a definite migratory instinct towards 

 Bolivia or the Chaco region in the winter season, there would not be so 

 many of these isolated and stationary swarms in such scattered districts 

 and so far from the Bolivian frontier. On the other hand, had Bolivia 

 contained an extraordinary number of locusts, it is remarkable that 

 three naturalists should have searched the region during the autumn 

 and winter months of 1917 without finding more than ten individuals. 

 It should be remembered that S. paranensis, contrary to the habits 

 of almost all the other Argentine locusts, passes the winter m the adult 

 stage. The zone within which it is possible for the species to hibernate 

 cannot in all probability be definitely determined, but in the author's 

 opinion it can be roughly defined as lying between parallels 25° north 

 and 32° south. This does not imply that there are no locusts in 

 Bolivia during the winter ; on the contrary there undoubtedly are 

 considerable numbers, and it is not denied that large invading swarms 

 sometimes migrate from that country, but it is not admitted that the 

 main focu§ from which all swarms appear is always to be found there. 

 The foci are variable and numerous, and the winter is passed wherever 

 the insect happens to be located, provided that the temperature is 

 suitable and there is sufficient sustenance in the neighbourhood. The 

 very obvious differences of opinion of authors who have discussed the 

 question of the migrations and permanent zones of the Argentine 

 locusts indicate the necessity for further investigations on the 

 subject. 



Certain recommendations are suggested for future mvestigations. 

 Observers should be stationed at intervals along the Bolivian frontier 

 to note any flights or settlement of swarms in that region. The exact 

 areas in which locusts hibernate throughout the country should be 

 determined over a number of years, so that control measures may be 

 concentrated on those areas. It would be of interest to determine, 

 if possible, the reason why the swarms cross certain regions of the 

 country only, e.g., the Misiones territory, and never visit, for example, 

 the south-east of the Province of Buenos Aires or the Puna region. 

 Similar plans of investigation should be followed in the neighbouring 

 repubhcs of Paraguay and Bolivia. It is suggested that a special 

 technical offi.ce should be established, with full authority, to study the 

 biology of the locust, its migrations, parasites, and the most modern 

 methods of dealing with it. 



This monograph concludes with a list of the species of Schistocerca 

 commonly accepted in 1910. 



