28 REPORT ON THE DISEASES OF SILKWORMS IN INDIA 



results have been achieved by the Department of Sericulture. 

 In two villages, Malurpatna and Hyndargoppa, where the silk indus- 

 try was on the point of dying out completely owing to losses from 

 pebrine, the department demonstrated that by rearing examined 

 seed in one of the rearers' houses, which was thoroughly disinfected, 

 a perfectly satisfactory yield could be got. In both places the 

 industry has revived and the rearers, using examined seed, are 

 getting full crops where formerly they could get none. 



What are the common sources of infection ? The results of 

 our census of disease have led us to believe that theC^iereditary source 

 of infection is very much more important than the contaminative) 

 but the latter is far from being negligible. A number of experi- 

 ments were conducted to see what the percentage of infection 

 was in caterpillars reared from diseased moths' progeny, what the 

 percentage of infection was in caterpillars from disease-free stock 

 reared in highly infected surroundings and also, in infected sur- 

 roundings, what was the commonest source of infection. 



Hereditary infection. Percentage oj disease in diseased moths' 

 progeny, (jt will be readily understood that even if a moth is heavily 

 diseased its eggs may not be very heavily infected, or indeed may 

 not be infected at all?) In this way the examination results in dis- 

 eased moths' progeny vary very greatly. A laying may give as high 

 as 100 per cent, disease or disease may be completely absent — 

 although it must be admitted that these extreme cases are rare. 

 Still no definite percentage of disease can be given as constant. If 

 progeny from a diseased moth of the 1st generation diseased be taken 

 during different rearing periods, the percentage of disease is found 

 to range from about 10 per cent, to 32 per cent. (Exper. 1). If 

 •progeny from a diseased moth of the 2nd generation be taken during 

 different periods, the percentage of disease is found to range from 16 

 per cent, to 69 per cent. (Exper. 2) : in one case no disease at all was 

 got, but as already remarked this is so exceptional that it is not 

 included. If progeny from a diseased moth of the 3rd generation be 

 taken during different periods, the percentage of disease is found to 

 range from 49 per cent, to 96 per cent. (Exper. 3). Therefore it 

 would seem that the more generations of disease behind them the 

 higher percentage of infection up to a certain point. 



In order to find whether there was any seasonal difference that 

 might explain the differences in amount of disease between the 

 different generations, lots 1 and 2 of Experiment 1 and lots 3 and 4 

 of Experiment 2 may be compared, as may lot 3 of Experiment 1 

 and lot 5 of Experiment 2. These lots from different generations of 

 diseased moths' progeny had practically the same rearing periods^ 

 and yet it will be seen that in every case (the first generation shows. 



