REPORT ON THE DISEASES OF SILKWORMS IN INDIA gj 



may now enquire if there are any special conditions that make 

 pebrine more difficult to control or in general more dangerous in 

 this than in other countries. 



There are three factors to be considered ; (1) the parasite, (2) the 

 worm or host and (3) the environment. The question of the parasite 

 may be dismissed in a few words. The organism is same in Europe, 

 India and Japan, and it runs the same course in the caterpillar. The 

 higher temperatures got in tropical and subtropical countries will 

 however tend to make its development more rapid than in cooler 

 countries. According to Vieil (1906), this is a decided advantage 

 and in the past prevented the complete sweeping out of the silk- 

 worms by pebrine in French Indo-China. According to this worker, 

 the rapid development of the parasite leads to the death of the 

 more highly diseased worms before spinning, or if they do spin 

 prevents pupation, so that the diseased worms are eliminated before 

 the time for laying eggs. In short the intensity of the disease lessens 

 the risk of hereditary infection. But as the life-cycle of the multi- 

 voltine worm is much more rapid than that of the univoltine worm 

 in temperate climates, I should have thought that this would tend 

 to more than outweigh the more rapid development of the 

 parasite. According to others, the rapid development of the worm 

 in the tropical countries prevents the life-history of the parasite 

 being completed and so the disease is less serious than in 

 temperate countries.* I think it is certain that the disease is 

 less devastating in the tropics than it wa's in Europe, and I believe 

 that this is to be explained by the rapidity with which the worm 

 goes through its life-cycle. There is less time for auto-infection to 

 spread the disease all through the body of the host. 



The silkworm of the tropics is nearly always multivoltine . Indeed 

 it has been shown in Madagascar by Fauchere (1913) that the uni- 

 voltine worm of the temperate zones becomes gradually multivoltine 

 in the tropics, and from this it is argued that the univoltine state 

 is an artificial one produced by transferring the silkworm from the 

 equable tropical climate to a climate of very variable temperatures 

 (European). The fact that in Bengal there is a univoltine worm 

 does not altogether disprove this contention, as the climate of Bengal 

 is not strictly tropical but has a considerable range of variability. 

 The multivoltine character of the Indian or tropical worm must 

 certainly have some effect on the question of disease. The Nistari 

 worm may be got to produce as many as 9 generations in a year 



* In 1913 it was said that pebrine in French Indo-China made much less havoc than it use d 

 to do in France and was decreasing. In Cambodia in 1914 it was said to be less serious and 

 showed no sign of wiping out the worms. In Madagascar in 1917 pebrine was said to be serious 

 partly on account of the carelessness of the native rearer, partly on account of the rapidity wiht 

 which one generation succeeds another. 



