928 MICROBIAL DISEASES OF INSECTS 



Dying larvae diseased with European foul brood frequently show 

 the segments of the body marked off less distinctly than living healthy 

 larvae. 



CAUSAL ORGANISM. B. pluton, the organism of European foul brood, is a small, 

 non-spore-forming organism, sharply pointed at one or both ends, about i/i long and 

 less than o.5ju in breadth, on the average; occurs frequently in pairs; single individuals 

 vary very markedly in size and shape. 



This organism has never been cultivated, but sections of larvae in various stages 

 of the disease show B. pluton to be the first invader of healthy larvae. B. pluton 

 gains entrance to the larva by way of the mouth. The growth and multiplication of 

 the parasite take place within the stomach and do not, during the life of the larva 

 get beyond the peritrophic membrane. The tissues therefore, are not invaded by it. 

 The secondary invaders in European foul brood, B. ahei, Strept. apis, Bad. eury- 

 dice, and B. orpheus, rarely, if ever, invade the tissues until the larva is dead or nearly 

 so. In American foul brood, practically speaking, there are no secondary invaders, 

 either during the life of the infected larva, or during the decay of the remains. 



Experimentally, B. pluton suspended in water, was killed at approximately 63 

 in ten minutes, but when suspended in honey, 79 for ten minutes had to be ap- 

 plied. Dried, B. pluton remained alive and virulent for approximately a year. In 

 the dry state direct sunlight was not destructive until after twenty-one to thirty-one 

 hours, but when suspended in water, only five to six hours were required for de- 

 struction, and when suspended in honey exposure for from three to four hours was 

 fatal. 



In the presence of fermentative processes in a 10 per cent sugar solution B. 

 pluton was destroyed in from three to five days at incubator temperature and in 

 from eleven to twenty-one days at room temperature. In a fermenting honey 

 solution outdoors, it was still alive and virulent after one month; in undiluted 

 honey at room temperature B. pluton ceased to be virulent in from three to seven 

 months. Mixed with pollen, this bacillus remained alive and virulent for more than 

 seven months at room temperature and for more than ten months at refrigerator 

 temperature. Putrefactive processes were destructive to B. pluton in from seven to 

 thirteen days at incubator temperature, in from twenty-one to thirty-five days at 

 room temperature, while at outdoor temperature it remained alive and virulent 

 for more than forty days, the maximum time not being determined. 



B. pluton was destroyed by 0.5 per cent carbolic acid solution in from eight to 

 eighteen days; i.o per cent required only five hours to four days, while 2 and 4 per 

 cent solutions required less than six hours. 



Neither man, the common experimental animals, nor insects other than honey 

 bees, so far as is known, are susceptible to infection with the European foul brood 

 bacillus. 



METHODS OF INFECTION % AND CONTROL. These are essentially the 

 same as those for American foulbrood. 



