196 INSECTS AND MAN 



existence in a diseased condition. This, however, is not 

 the only way in which " pebrine " is spread the excrement 

 of infected larvae is charged with parasitic spores, and, fall- 

 ing among the mulberry leaves on which healthy larvso are 

 feeding, these spores become scattered, and they are eventu- 

 ally devoured, thus setting up the disease in new hosts. 



With this double method of infection it is plain to see 

 that hundreds of thousands of caterpillars may be infected 

 in a short time. The fact that the eggs themselves may 

 be contaminated accounts for the rapid spread of the 

 disease to districts where it was previously unknown, for 

 it is in the egg stage that these insects are sold com- 

 mercially and conveyed from place to place. Thanks to 

 Pasteur's efforts, drastic measures were enforced, and 

 "pebrine" was practically banished. Of remedies there 

 were none, so the parent silkworm moths were sorted out 

 and put into separate breeding cages, a male and female 

 in each. After oviposition, the parents were killed, if not 

 already dead, and their bodies were macerated and examined 

 for Nosema bombycis ; if the parasites were found, the eggs 

 were all destroyed, only eggs from healthy parents being 

 allowed to hatch. Great credit is due to the proprietors 

 of the silkworm farms for so faithfully carrying out this 

 crusade at enormous expense to themselves, and, although 

 " pebrine " is now mainly of historical interest, it merits a 

 place of honour in every book on economic entomology, if 

 only as an example of what can be done in the way of 

 stamping out disease, if the findings of scientists are 

 efficiently discharged by those who alone can make them 

 effective farmers and gardeners. 



An allied disease, popularly known as the " Isle of Wight 

 bee disease," because it made its first appearance in that 

 island in 1904, has caused serious losses to bee-keepers in 

 this country. The causative agent is a parasite, Nosema apis. 

 Both parasite and disease have many points in common with 

 " p6brine," though hereditary infection is unknown. 



