THEIR RELATION TO WEATHER 151 



drastic measures. Many years ago the breeders of silk- 

 worms in France found their caterpillars dying at such 

 a rate as to threaten the very existence of the industry. 

 It was a germ disease of course, but nothing was known 

 of such things at that time and it afforded an oppor- 

 tunity for Pasteur to win renown and to benefit his 

 fellows to a degree that few in that or any other country 

 have really appreciated. It gave a striking illustration 

 of what epidemic disease could do under favorable 

 conditions, and it is still suggestive as to possibilities 

 when we attempt to reverse the Pasteur objective. 



At the present time many bee-colonies are suffering 

 from what is known as "foul-brood," a disease or dis- 

 eases of micro-organic origin which carries off enormous 

 numbers of specimens annually. The character of the 

 organisms causing these diseases is now known and, 

 in a general way, the treatment to be adopted, so there 

 is nothing at all mysterious except the negligence of 

 the bee-keeper who permits the disease to develop un- 

 checked in so many instances. It is probably rare that 

 an insect once attacked by disease, recovers. In my 

 breeding experiences and in field observations I have 

 never known of such a case. I have often seen among 

 a brood that sickened, one or a very few individuals 

 that showed no trace of disease, that fed normally 

 and developed naturally ; but I have never seen such 

 a larva show signs of the sickness and then resume 

 growth; so in a general way these diseases may be con- 

 sidered as fatal when they once gain a foothold. 



We have now seen that, while in general there are 

 no conditions of climate where insects do not occur, 

 yet climatic conditions may and do in many cases 

 check not only the distribution but the numbers of 

 insects: that while many species are fitted to live under 

 widely varying conditions, others are adaptable within 



