CLIMATE AND WEATHER 257 



The technique of the latter, it may be added, has greatly improved 

 in recent years, and is dealt with in the recent books by Chapman 

 (1931) and Shelford (1929). It will, therefore, become evident 

 that two parallel lines of inquiry are desirable, one applicable to 

 actual field conditions and the other to be prosecuted in the 

 laboratory. Taken in conjunction, they are more likely to advance 

 knowledge than if laboratory experimentation be pursued without 

 reference to field conditions ; in other words, the latter provide 

 the real problems which are to be taken to the laboratory for 

 analysis. 



Climate and Weather in Relation to Seasonal Prevalence. The 

 relations of climate and weather to seasonal and periodic behaviour 

 of insects afford more difficult problems than those governing the 

 general distribution of those animals. In certain parts of the 

 tropics the climate is extremely uniform throughout the year, 

 with relatively small fluctuations of temperature around either 

 the daily or the annual mean. Under such conditions seasonal or 

 periodic behaviour of insects is but little pronounced. True 

 dormancy, for example, is almost a non-existent phenomenon, 

 and insects are able to pass through uninterrupted cycles of 

 development and activity from year to year. In other parts of 

 the tropics, where there are sharply contrasted dry and wet 

 seasons, the former with a prevailing high temperature and the 

 latter with a cooler temperature, these changes are directly 

 reflected upon the insect life. The incidence of special dry and 

 wet season forms, for example, is well known in Lepidoptera, but 

 the most marked phenomenon is the tendency of the life-cycle in 

 most insects to be interrupted during the dry season. Heat and 

 drought, often accompanied by leaf-fall, are prejudicial to insect 

 life in general, and it is at this period activity becomes arrested 

 and a condition of aestivation is entered upon. In temperate and 

 cold regions the most prejudicial period is the winter, when insect 

 activities attain their minimum and the phase of hibernation 

 supervenes. Hibernation and aestivation, in the true sense of 

 those terms, are so deeply impressed upon the species, as the result 

 of environmental influences affecting many thousands of 

 generations, that these phases have become definite rhythms 



R.A. ENTOMOLOGY. 9 



