September 20, 191 7] 



NATURE 



47 



teen species of "locust" on the earth, but the 

 memoir lists 112 of the family Acridiidae (called 

 Locustidae). Allowing for this, the memoir pro- 

 vides an excellent summary of habits, life- 

 histories, remedies, and international co-opera- 

 tion. 



It is curious that human ingenuity has not 

 succeeded in controlling locusts, or even in 

 understanding why an insect, normally wide- 

 spread in small numbers, becomes enormously 

 abundant, packs into swarms, and migrates over 

 really enormous distances. One reason is that 

 no single observer in his lifetime can get a long 

 enough experience to be able to estimate the 

 value of the different factors that govern these 

 outbreaks ; they are probably so diverse that a 

 very minute knowledge of local conditions is 

 required, and in any one locality there may not 

 be sufficient outbreaks during a single working 

 lifetime. So we still know very little of the con- 

 ditions producing outbreaks, or the means of 

 anticipating them and preparing for them. The 

 methods in use are most diverse and as a rule 

 extremely simple. In India troops have been 

 turned out to fire volleys of blank cartridge to 

 divert a swarm ; while in Morocco cultures of 

 Coccobacillus acridiorum have been used with suc- 

 cess. These two represent the extremes of sim- 

 plicity and of scientific achievement; but a 

 perusal of this memoir shows that the locust 

 problem still remains and looks like doing so. 

 As the author says, " II existe toujours une ques- 

 tion des sauterelles," and in the main the pest 

 must be fought in every country with simple, 

 homely methods devised to suit the local circum- 

 stances : the arsenic-treacle method succeeds in 

 South Africa, but not in India; the method of 

 "mopping up " hoppers in Bombay with a bam- 

 boo frame and bag is useless elsewhere; and 

 there is no one method that stands out definitely ! 

 as likely to be valuable. 



To the economic entomologist, who is prob- 

 ably a member of an agricultural department, 

 locusts present a serious problem, calling for 

 whatever ingenuity he possesses. In 1903 there 

 broke out in Bombay a plague of locusts of 

 unknown habits, which actually flew about for 

 eight months before laying eggs, and then sud- 

 denly the entomologist was called on for a means 

 of dealing with hoppers about to hatch from 

 eggs laid over 150,000 square miles of country. 

 Such occasions are crises in the life of the en- 

 tomologist, and we commend Prof. Trinchieri's 

 summary as a welcome source of inspiration when 

 faced with an outbreak. 



In his last section the author discusses shortly 

 the value of international co-operation, a matter 

 that has been prominent since the Phytopatholo- 

 gical Conference was held in Rome. Sixteen 

 countries have answered in the affirmative the 

 institute's query as to their willingness to co- 

 operate against locusts. The value of such 

 co-operation lies in the intelligence mutually 

 given as to the occurrence of locusts, and this 

 would be most valuable. It is useless discussing 

 NO. 2499, VOL. 100] 



this at present. Locusts do not respect interna- 

 tional boundaries or join the Entente; but it is 

 a part of the valuable work done by the institute 

 that we should have these memoirs and be pre- 

 •pared for international co-operation when other 

 circumstances render it possible. H. M.-L. 



BIRD MIGRATION IN CENTRAL SWITZER- 

 LAND IN RELATION TO METEOROLOGICAL 



CONDITIONS.' 

 T^HE relation of bird migration to meteorological 

 -*• conditions has been considered, of late years, 

 an important part of the study of the movements 

 of birds, and various theories have been 

 advanced to explain their interrelations. In 

 the memoir before us Dr. Bretscher deals 

 very fully with the arrival in spring and 

 departure in autumn of the summer visitors to 

 Central Switzerland. In relation to these he 

 treats of bird migration and atmospheric pressure, 

 wind, atmospheric precipitation, temperature, etc., 

 and under each heading he has tables of statistics 

 in support of the statements in the text. By 

 tables 1 and 15 he shows that the position of 

 barometric depressions within the area has, as 

 we should expect, no influence on the arrival of 

 the summer migrants and their departure in 

 autumn. In tables 3 and 4 he discusses the in- 

 fluence of direction and strength of the wind, and 

 concludes that, in Central Switzerland, migration 

 proceeds irrespective of the direction of the wind, 

 and that, unless the force be so great as to be a 

 hindrance, the influence of this, too, may be re- 

 garded as a negligible quantity. The fourth 

 section deals with atmospheric precipitation in 

 relation to bird migration ; as the author tells us 

 in Switzerland even keen ornithologists stay at 

 home in wet weather, we are not surprised to find 

 that they have few direct records of migration in 

 rain, snow, or fog, and he himself says, further 

 observations on this subject are wanted. 



What strikes one as being the most interesting 

 of any of the sections are those on spring and 

 autumn migration in relation to temperature. 

 Dr. Bretscher gives many interesting tables show- 

 ing the number of observations on the movements 

 of each species under each degree of temperature 

 Centigrade. These indicate the maximum and 

 minimum between which migration takes place, 

 the gradual increase to the most favourable 

 migration temperature, and the decrease after this 

 is reached. Here we see that birds migrate be- 

 tween certain temperatures, which vary according 

 to the species; thus, the blackbird and song- 

 thrush perform their migrations at a lower 

 temperature than the insect-eating warblers. 

 Another aspect is presented on table 9, namely, 

 the duration of the migration period in relation to 

 the average temperature, and the author here 

 comes to the conclusion that the two are not 

 correlated ; thus the warmest average temperature 

 does not necessarily coincide with the shortest 



1 " Der Vogelzuj; im schweizerischen Mittelland inseiiiemZusantimfnhang 

 mit den W!tteruiigsverhaltni«xen." Voii Dr. K. Brettcher. Noiiveaux 

 mimoiies de la Socirftc- Helv^tique des Sciences naturelles, vol. li., mem. 3. 



