290 I'X'OXOMR' EXT0MOL0(JY IN MOrAMinQUE. 



mologists, has rightly maintained that " life history work is the 

 basis of all economic entomology." While this statement has 

 never been challenged, the interpretation of the expression " life 

 history " has often been very varied. What I mean is that, in 

 many instances, " life cycle " has been considered synonymous 

 witli " life history." 



In order successfully to combat an injurious insect it is, of 

 course, essential that we should know what are the different 

 stages it passes through in its development, and at what time 

 during the season these stages occur, so as to find out its weakest 

 stage, when it will be most successfully destroyed by the applica- 

 tion of insecticides or other methods of control. Valuable as are 

 the data gained by such an investigation, they are not sufficient 

 to allow us to control the insect in the most effective and most 

 economical manner, and I take this opportunity to make a plea 

 for breaking away from the old time-honoured methods of insect 

 control and seeking for new ones. Tlie methods thus far 

 employed, and first introduced and worked out in detail by the 

 pioneers in economic entomology of the United States Depart- 

 ment of Agriculture, have undoubtedly saved millions of pounds' 

 worth of crops, and agriculture owes them a debt which it can 

 never repay. Nevertheless, our present methods are artificial, 

 expensive and cumbersome. In Nature we find that it is onl}' 

 under very exceptional conditions that the wild vegetation is 

 destroyed to such an enormous extent as we find taking place 

 year after year with our cultivated crops, and, even if this 

 happens during one season, the balance is quickly restored. The 

 reason is not far to seek. Nature has provided an extremely 

 complex system of balancing factors, influencing the abundance 

 of the various species of plants and animals. There are climatic 

 conditions, such as alternate heat and cold, abundance, intensity, 

 ])eriodicity of rainfall, even in the case of some insects, the 

 presence or absence of sunshine, humidity and texture of soil, 

 atmospheric movements, all of which may have an influence at 

 times on the development of certain insects. Besides, there is 

 another complex of parasites, primary, secondary, tertiary, even 

 quarternary, predaceous enemies, each and every one of them 

 forming, as it were, a cog in the complicated machinerj'. 'As an 

 example, I may mention the sugar cane leaf hopper (PcrhinsieUa 

 sdccharina), in Hawaii, where the parasite complex comprises 

 some forty species of insects alone, not mentioning insect-eating 

 birds and destructive fungus diseases. Interference with the 

 normal development of any one of these forty will, in its tum, 

 affect the abundance of the thirty-nine others, and thus ultimately 

 that of the host. Now, each of our insects, injurious or otherwise, 

 is the centre of a similar complex — in most cases as yet unknown 

 to us — and it should be possible by interfering intelligently with 

 one or more members of this complex so to influence the original 

 host as to redi;ce its injvu-iousness considerably, thus counter- 

 balancing the factor of abnormally abundant food supply intro- 

 duced bv the agriculturist. In our ignorance we have concen- 



