238 SOME ASPECTS OF ECOLOGY 



ment, however, to kill the surviving adults of every species, but 

 that duration proved insufficient for the complete extinction of 

 th<=^ larvae of Attagenus piceus, Tenebrio ohscurus and Trogoderma 

 tarsale. The last-mentioned species proved the most resistant 

 and suffered a mortality of only 30 per cent. These results are 

 not in accord with those carried out in the bell- jar experiments, 

 when complete mortality of the insects in all their stages occurred 

 within four days. The experiments prove, however, that 

 individuals of certain species of insects can withstand several 

 days' subjection to an almost complete vacuum. The treated 

 specimens, it may be added, were retained for two weeks after 

 the experiment and frequently examined to ascertain whether 

 recovery took place. 



Air Currents 



Within the last fifteen years or so some attention has been given 

 by Coad (1931) and others in America, and more recently by 

 Berland (1934) in France, to the carriage of insects by currents of 

 the upper air. By the adoption of trapping arrangements 

 attached to aeroplanes, small insects, including a good many 

 wingless forms, have been collected up to an altitude of at least 

 14,000 feet. Once such creatures become carried upwards by 

 convection or other movements it would appear that it is possible 

 for them to be transported long distances, since the upper air 

 currents are stated to be both strong and constant in direction. 

 Buxton (1935) in discussing the Samoan fauna, concludes that a 

 number of facts concerning the distribution of the insects can be 

 best explained on the supposition of their having reached the 

 islands via the upper air. It is obvious that when a more extended 

 study of insects occurring in the upper air has been undertaken 

 we may be in a position to be able to account for some of the 

 anomalies of insect distribution. It has also certain very obvious 

 economic implications regarding the entry of injurious species 

 into lands which they did not previously inhabit. Furthermore, 

 quarantine regulations naturally have to be considered in a new 

 light, and previously unaccountable cases of their inefficacy seem 

 now to be explained. The fortuitous transport of noxious 



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