REPORT ON THE DISEASES OP SILKWORMS IN INDIA 43 



some particular degree — the object of the crossing having been 

 of course to produce a vigorous worm that produced better silk 

 than the Nistari. It is outside the scope of this investigation to 

 go into the question of hybridizing, but it seems to have been under- 

 taken in the most light-hearted fashion without any preliminary 

 inquiry into the various characters of the worms and the ways in 

 which they were inherited — on the whole a rather haphazard 

 business. Now as we shall see later, the Nistari does seem to be 

 resistant to rot diseases and is in general a very sturdy worm, but no 

 experiments seem to have been conducted to see how far this was 

 true and to what extent this was a heritable factor. Similarly 

 with the richness of silk, which it was desired to get from the foreign 

 worm, no work was done to see in how far this depended on climate, 

 food, etc., rather than on some factor in the germ cell of the foreign 

 worm. So far as I can see the results have not been more satis- 

 factory than one would have expected from the methods employed. 

 The best hybrids are a little better than the best Nistari at certain 

 periods of the year, but they seem to be gradually deteriorating. 

 In connection with this the observations of Grangeon (1917) 

 are of the utmost importance. He decided that it was impossible 

 to combine hardiness with richness in silk. He found that on first 

 crossing Nistari with European or Madagascar worms, worms which 

 gave a very good yield of silk were got, but in the succeeding genera- 

 tions the - richness becomes less marked and the worms finally 

 divided up into two classes — a small resistant worm and a large 

 worm with less resistance which died out. From this it would seem 

 a,s if the attempt to increase the resistance of worms by hybridizing 

 was not likely to be a success. It may further be noted that almost 

 certainly the quantity and perhaps also the quality of silk in a 

 cocoon has more to do with climate than anything else (Coutagne, 

 1902). Much work on tropical sericulture has been done in Mada- 

 gascar and the opinion of Fauchere (1913) is all in favour of this 

 view. His contention is that silkworms are to be regarded as of 

 tropical or sub-tropical origin and that the multivoltine condition 

 is the normal one, the univoltine condition being artificially induced 

 by rearing in climates of very variable temperature, but that very 

 hot and moist climates do not allow of production of first quality 

 silk. 



Before undertaking any selection or hybridizing work, whether 

 to improve resistance or to increase the yield of silk, the work that 

 has already been done on sericulture in the tropics should be very 

 carefully considered and then preliminary work should be under- 

 taken to determine what is due to environment such as climate, 

 food, etc., and what to actually inherited characters. When the 

 ground has been thus somewhat cleared it will be seen whether any- 



