BEES IN COLONIES AFFECTED BY EUROPEAN FOULBROOD 21 



tention of the honey stomachs by the retention of the colored sirup 

 therein. About half the bees in the hives were discolored in this 

 manner. After a day or so, however, this begin to disappear. Also 

 the number of cells showing the pink discoloration began to disappear. 

 Evidently the sirup had been moved up, worked over, and mixed with 

 other nectar or consumed. 



Later, some time after the heavy honey flow had started, shortly 

 after July 1, two more colonies were fed colored sirup, this time 

 infected with diseased larvae macerated therein. 



In these cases the discolored abdomens were noted about as before, 

 but the colored cells were less numerous and the color less striking. 

 The location of the colored cells was similar to that in the former ex- 

 periment ; that is, mainly in the brood area or just contiguous to it 

 and mostly above. The outside combs, containing considerable honey, 

 showed scarcely any of the colored cells. This time these colored 

 cells disappeared sooner, showing that the infected material must 

 have been much diluted quite soon after being taken up from the 

 feeding dishes. 



Figure 6 shows the method of plotting the location of diseased 

 larvse in the combs and also the location of the cells containing the 

 colored sugar sirup. As will be noted, a fairly large proportion of 

 these cells are located within the area of brood at the time of feed- 

 ing. It is interesting to note the tendency of diseased brood to form 

 concentric circles, showing the two series of larvae occurring between 

 the dates noted. The spreading was from two cells at first to quite a 

 large number at the last observation shown. 



AGE AT WHICH LARV^ ARE INFECTED 



In previous observations it was constantly noted that the larvae 

 affected by European foulbrood were regularly at least 4 days old, 

 the age at which the coiled larvae completely fill the bottom of the 

 cells. Occasionally a slightly younger and smaller larva would 

 become diseased, but this was not the common occurrence. Further- 

 more, in the cases where the colored sirup was fed the bees, within 

 24 to 36 hours quite a number of larvae averaging 4 days old could be 

 seen discolored from having been fed this sirup, while it was notice- 

 able that the younger larvae under 3 days old never showed the dis- 

 coloration. These colored larvae were examined in a smear under 

 a microscope, but the infecting organisms, being comparatively few 

 in number, had not increased sufficiently at that time to be apparent. 



The question now arises as to the age at which the larvae first are 

 fed nectar or infected material. There has been much controversy over 

 the subject of composition and source of the larval food, but as yet no 

 conclusive scientific evidence has been presented. Irrespective of 

 the question whether the food at various stages originates from 

 glands or is regurgitated, it is apparent from these observations that 



