REPORT ON THE DISEASES OF SILKWORMS IN INDIA 41 



the infection may spread more rapidly in the caterpillar's body. 

 In this way the parasite seems to have rather the upper hand and 

 the caterpillar has not been able, so far as one can see, to cope 

 with the parasite very efficiently when present in large numbers— 

 so long as infection is slight the original balance seems to be main- 

 tained. *fv*j 



It is therefore very essential that we should determine what 

 factors, if any, are likely to help the caterpillar to resist this mass 

 attack. Now, it is a well known fact that immunity in men — who 

 are animals singularly susceptible to disease — and other mammals 

 varies according to individuals, according to the health of the 

 individual at the time of attack and also to countless and often very 

 minute variations in the environment — such as in temperature, 

 moisture, amount and kind of food, etc., etc. In absence of evidence 

 to the contrary we may presume that silkworms are similarly cons- 

 tituted. We may inquire first if it is possible to discover more 

 resistant races of caterpillars and by selecting from them or using 

 them in hybridizing experiments to evolve a highly resistant race, 

 and second what are the conditions under which silkworms are most 

 healthy and what can be done to secure these conditions and so- 

 raise their resistance by improving their surroundings. 



Personally I think the search for a resistant race, or at all events 

 a race more resistant than the local Indian ones, will not be crowned 

 with success. These races have been bred for many generations 

 under very trying circumstances, and it is reasonable to suppose 

 that the fittest and most resistant worms have survived and form 

 the present stock. . It is significant that all attempts at introducing 

 fresh stock have failed so far as one can find out from the records — 

 the foreign races have not been able to stand the climate and the 

 treatment meted out to them. That even European varieties can 

 be reared with care in the plains of India is true, but that does not 

 invalidate the above statement, for they could not survive one 

 season under the ordinary rearing conditions in the villages. That 

 introduced races fall especially a prey to pebrine I do not say — 

 it is indeed usually flacherie or some similar rot disease that carries 

 them off. In point of fact while I believe that worms vary very 

 greatly in their resistance to rot diseases, I think the evidence shows 

 that they are all more or less alike in their resistance to parasitic 

 diseases. It is claimed by Mukerji (1899) that the Chhotapolu is 

 more susceptible to pebrine than the Nistari and both more so than 

 the Barapolu, but Mukerji's evidence is far from convincing. 

 He also states that dark coloured or black caterpillars are more 

 vigorous than the ordinary races, citing Cleghorn's black Bara- 

 polu. An exactly similar worm seems to have been selected by- 



