36 TECHNICAL BULLETIN 14 9, U. S. DEPT. OF AGKICULTUEB 



coating. Later on the spore walls became thicker and roughened 

 while changes of a chemical nature result in hardening of the gelatin- 

 ous covering. This additional protection in old spores from the 

 digestive fluids of the bee may explain the ability of old spores to 

 attack bees and the complete lack of this ability in young spores. 

 After germination, the digestive fluids of bees appear to have no 

 injurious effects upon the young mycelium. 



Two other cultures of A. ockraceus, isolated from bees but differing 

 in morphological and cultural characteristics from this form, failed 

 to parasitize bees or brood I'egardless of the age of the spores. 



A few species of Aspergillus, among them A. versicolor, A. terreus, 

 A. cwndidus, A. sydowi, A. svZphureus, and A. clavatus, isolated from 

 beehives or bees, failed to infect bees in cages. Colonies of bees, 

 therefore, were not tested with these organisms. The mycelium of 

 these species was superficial on bees, and the characteristic mum- 

 mification, common in mycosis, was absent. If these species ever 

 attack bees, it would appear that special conditions are necessary. 



The Penicillia appear to have only a purely saprophytic relation 

 to bees. The resemblance of bees mummified by any of a number of 

 species of Penicillium to those dead of mycosis may be explained by 

 the rapid saprophytic growth within the bee immediately after death. 



The frequency with which the Penicillia occur on bees may be ac- 

 counted for, at least in part, by their ubiquitous nature and by the 

 fact that the spores are not quickly killed by the intestinal fluids. 

 Viable spores in large numbers are usually present on the brood 

 combs and equipment within the hive. When Penicillium spores 

 gain entrance to the alimentary canal before death, they may grow 

 saprophytically within the bee after death. 



The only damage to bees for which the Penicillia are responsible 

 is caused by their saprophytic growth within the hive. Since the 

 conditions of moisture and temperature within strong, well-managed 

 colonies rarely permit the growth of fungi on the combs, damage is 

 generally limited to poorly ventilated hives, weak colonies, and 

 combs in unoccupied hives. 



Mucors have been found to occur commonly on bees, but the experi- 

 mental evidence thus far obtained indicates that ordinarily they are 

 not patliogenic. Sporangiospores may swell considerably or even 

 bud once or twice in a yeastlike manner within the ventriculus with- 

 out seriously injuring the bee. It was found by cultures from the 

 ventriculus and rectum of inoculated bees that sporangiospores of 

 most of the Mucors investigated were soon killed by the intestinal 

 fluids of adult bees. Inoculated bees that later died of starvation 

 were not attacked by the Mucor after death. 



It appears, however, that, under certain conditions which as yet 

 have been only partially determined, bees are parasitized by one or 

 more species of Mucor. In the inoculation experiments with Mucor 

 hiemalis an occasional bee died of infection. This species has often 

 been isolated from mycelium found vegetating in sick bees and from 

 dead bees. 



The results of investigations with this Mucor will be given in 

 another paper. 



Inocidations with other filamentous fungi that commonly occur on 

 bees have always given negative results; consequently the writer is 



