14 REPORT ON THE DISEASES OF SILKWORMS IN INDIA 



seriousness of the disease. Where no measures are taken to cope 

 with it, it causes great loss and it is undoubtedly a serious menace 

 to the success of sericulture in this country ; but it is this constant 

 and real lessening of the silk yield through pebrine that is to be 

 feared and guarded against rather than some problematical epidemic 

 of the future. 



History and life-history of the causal organism. The 



disease pebrine is caused by a protozoan parasite belonging to the 

 order Microsporidia of the subclass Neosporidia of the class Sporozoa. 

 The large class of the Sporozoa are without exception parasites, and 

 the order Microsporidia are pre-eminently parasites of Arthropods, 

 that is to say of Insects and Crustacea. The organisms belonging 

 to this order were first discovered during the investigations into the 

 terrible epidemic of pebrine that swept through the silk-rearing 

 districts of Europe and the Near East between 1850 and 1870. * It 

 is to Leydig and Balbiani that we owe the first really scientific 

 investigations of this group. These workers discovered parasites of 

 this order not only in silkworms, but in other caterpillars, in beetles, 

 in crane flies, in bees, in scale insects, in spiders and in water-fleas 

 (a small crustacean). More recently, members of this same order 

 have been described from the river crayfish and from some fish such as 

 the flounder and the stickleback, as well as from many other insects 

 than those named above. The Microsporidia are thus not by any 

 means a very small group of parasites, nor are they of very recent 

 discovery. They are characterized by the production of minute oval 

 spores of a somewhat peculiar construction. In the genus Nosema, 

 to which the pebrine organism belongs, each organism produces only 

 one spore, the other genera in the order producing more than one 

 spore per individual. Before proceeding to the description of 

 Nosema bombycis and its life-history, it may be mentioned that 

 another species in the same genus, Nosema apis, a well known 

 parasite of bees, was at one time supposed to cause the Isle 

 of Wight bee disease, but is now known not to be responsible 

 for this terrible pest causing only a mild form of sickness — 

 Nosema disease — with very low mortality (White, 1919). It is 

 an interesting point, however, that the only two insects really 

 domesticated by men should be infected by such closely related 

 parasites. 



In describing the life-history of Nosema bombycis I do not propose 

 to enter into any scientific details regarding its development. I 

 want merely to give a general outline which may be of use and of 

 interest to those engaged in sericulture in India. For details see 

 Stempell (1909) and Kudo (1916). 



The spore, which has been mentioned above, is the most suitable 



