INDIGENOUS PARASITES 



407 



at the experiment station with those represented by the average 

 for the State as a whole is given below. 



With increasing knowledge of host and parasite behaviour, 

 instances where analogous methods may appear to be applicable 

 will undoubtedly be multiplied. On the other hand, it is difficult 

 to prove that any observed effect is due to the method in question. 

 Also, such methods are not likely to prove effective unless they 

 be carried out by general agreement among cultivators over a 

 wide area ; under more restricted circumstances only a fraction 

 of the insect population would be affected, and no appreciable 

 result is likely to supervene. 



Direct Increase of a Parasite Population. It has been contended 

 on theoretical grounds that the alteration of the host-parasite 

 ratio in specific cases by the artificial quantitative breeding of 

 suitable parasites is an evident possibility. A species of parasite 

 whose behaviour appears to lend itself favourably to the application 

 of the idea is the Chalcid Trichogramma minutum Riley, one of 

 the best known of all egg-parasites. It has a wide geographical 

 range, while its hosts include over 50 species of Lepidoptera, 

 including such notable pests as the sugar cane borer {Diatrcca 

 saccharalis Fab.), the European corn-borer (Pyrausta nubilalis 

 Hub.), and the codling moth (Cydia pomonella L.). Early in 

 the season this parasite is relatively scarce, while its spread is 

 slow owing to its limited power of distribution, but it is maintained 

 that if intensive infestation can be induced at the right time 

 potential outbreaks of certain pests might be largely counteracted. 

 At the present day attention is being centred on this parasite in 

 many parts of the world, and it promises to be the first species of 



