ARTIFICIAL USB OF CHECKS. 67 



will see ways in which he can turn his knowledg-e to good use either in 

 preventing the occurrence of such pests or in checking them. 



A subject that has unfortunately attracted general attention is the 

 fascinating one of using one insect to destroy another. "We know that 

 there are parasites, predators and the like which destroy insect life ; the 

 inference is that we should be able to check all our pests by their means. 

 Entomologists have devoted great attention to this point, with an almost 

 complete record of failure. In one instance, under very peculiar condi- 

 tions, success was attained, a ladybird beetle being introduced to 

 destroy a virulent insect pest. The particular conditions in this case 

 were that the pest was newlij introduced, had no enemies in the locality 

 to which it was introduced, and could be traced to the country whence it 

 came. It was not difficult to obtain from that country the beetle that 

 there preyed on it, and liberate it where it could find its accustomed 

 prey, which was the only insect it recognised ; it utterly destroyed the 

 pest, partly because it had no other food and partly because it had no 

 enemies in that place. Evidently this could be repeated with some 

 chance of success, but only in the case of newly introduced pests. Our 

 pests in India are probably of long standing ; they have enemies here, but 

 the fluctuations in the balance of life occasionally enable them to be 

 destructive. No parasite, no enemy will entirely destroy an insect that 

 is established throughout India, and there is no advantage to be gained 

 by introducing fresh parasites. There is also no ground for believing that 

 in the near future we shall be able to artificially employ fungoid and 

 bacterial diseases in the destruction of insect pests ; they appear to 

 require special climatic conditions {e.g., very moist heat), and this places 

 the matter beyond our control. 



What is of extreme practical importance is to encourage, not 

 particular parasites that are already doing their utmost under conditions 

 beyond our control, but birds which will destroy any insect that becomes 

 too numerous. Birds are the fluctuating check on insect life, the safety 

 valve as it were ; they congregate where they lind insects, regardless of 

 their species or habits, and constantly consume the superfluous and 

 superabundant insect life. We can encourage birds by planting trees, by 

 letting them take a not too excessive toll from the fields ; and every' 

 insectivorous kind means a large diminution in our pests. We cannot 

 as yet equally encourage other beneficial organisms, but must rely on our 

 own efforts to check the superabundant insect life that destroys oui' crops. 



