HOMO MILITANS 



under the influence of changes in environmental conditions, could 

 manifest their presence and potency. 



A balanced survey of what the economic entomologist nowadays 

 has wrought to protect mankind falls outside the scope of this lecture, 

 and is also beyond my competence. However, let me illustrate by a 

 single example the range and importance of the work of this variety 

 of Homo militans. I have chosen the fight against locusts because this 

 has also shown the need for international cooperation. It is but nec- 

 essary to recall the biblical description of the 'eighth plague' in Exo- 

 dus 10 in order to realize that from olden times locust plagues have 

 been dreaded by many peoples as harbingers of famine and misery. 

 For centuries man's only defense has consisted in a hopeless and in- 

 effectual attempt to destroy the insects there where they settled down 

 in swarms. A new element in the war against this plague was intro- 

 duced in 1 92 1, when Uvarov formulated his phase theory of locust 

 development. This investigator established that the larvae of many 

 locust species frequently begin by developing into the so-called solitaria 

 phase, differing both in shape and in behaviour from the swarming 

 insect to such an extent that it was believed to represent a different 

 species. During this phase it causes little damage, and its migration is 

 limited. But when conditions cause a great many of these solitarias to 

 aggregate in a small region, they develop into the morphologically 

 distinct gregaria phase which is extremely voracious, and shows a 

 strong tendency to mass migration. 



International investigations have clearly demonstrated the great 

 significance of this developmental history for the problem of warfare 

 against locusts. Thus it has been established that the swarms of the 

 African locust, Locusta migratoria migratorioides, which in 1928- 193 7 rav- 

 aged no less than 10 million square miles in such distant parts as 

 British and French West Africa, the Belgian Congo, Sudan, Eritrea, 

 British East Africa, and Rhodesia, were all initiated by the solitaria 

 phase occurring within an area of only ten thousand square miles, in 

 the swamplands of the Niger in the French Sudan. 



The various investigations have clearly shown that the rational 

 means to prevent disasters in far removed regions consists in controll- 

 ing the development of the relatively harmless solitaria phase. Obvious- 

 ly, this requires international cooperation. During the Fifth Interna- 

 tional Locust Conference in Brussels, in 1938, it was therefore recom- 



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