924 MICROBIAL DISEASES OF INSECTS 



broths to which a little brood filtrate or egg suspension has been added. Gelatin, 

 no growth in plain or in brood-filtrate gelatin at temperatures at which it remains 

 solid. 



The more resistant spores of B. larva require 100 for eleven minutes to destroy 

 them, and when suspended in hone> require a half hour or more. Five per cent, 

 carbolic acid is resisted for months, i-iooo mercuric chloride for days, 10 per cent, 

 formalin for hours, and 20 per cent, formalin for thirty minutes, in each case at 

 room temperature. In fact, most destructive agencies are resisted by these spores. 

 Drying at room temperature has been resisted for nine years, and it is most likely 

 that they will remain viable and virulent for a very much longer period. Dry 

 spores exposed to direct sunlight are killed in from twenty-eight to forty-one 

 hours. Four to six weeks are required for destruction when suspended in honey 

 and exposed to the direct rays of the sun, but if shielded from direct sunlight, the 

 spores remain alive and virulent for more than a year. The destructive effects of 

 fermentation have been resisted for more than seven weeks at incubator and out- 

 door temperatures, and it is likely that a much longer period could have been 

 withstood. 



B. larva is pathogenic for the larval, prepupal, or early pupal stages of the brood 

 of honey bees. Adult bees, rabbits, guinea pigs, rats and humans are not suscepti- 

 ible to infection. 



METHODS OF INFECTION. Natural. American foul brood infec- 

 tion is transmitted primarily through the food of bees; possibly at 

 times to some extent through their water supply. Robbing from the 

 diseased colonies of the apiary, or from neighboring apiaries, is the 

 most likely mode by which the disease is transmitted in nature. The 

 placing of brood combs containing diseased brood with healthy colonies 

 will also result in the transmission of the disease. It is not likely that 

 infection ever occurs through the. medium of flowers. Queens and 

 drones have been presumably overestimated at times as possible sources 

 of infection. It has not been determined as yet whether American 

 foul brood is ever transmitted by them. The clothing or hands of 

 those about an apiary or handling the bees are not fruitful sources for 

 the transmission of the disease. The hive tool, if brought in direct 

 contact with dead larvae in testing for the presence of disease, might 

 serve to transmit infection, but during the usual manipulation it would 

 not. Other tools and bee supplies generally about an infected apiary 

 will not transmit the infection in the absence of robbing from those 

 sources. 



Artificial. American foul brood can be communicated by feeding 

 to a healthy colony the scales from combs which had contained brood 



