DIAGNOSING BEE DISEASES IN THE APIARY 15 



of yellow than in affected larvae. Dissecting sick or recently dead 

 larvae and examining the contents of the digestive tract helps in 

 making a diagnosis after experience has been gained, 



CHANGES CAUSED BY DECAY AND DRYING 



The appearance of the dead larvae changes gradually during de- 

 cay and drying. The gray and the yellow colors deepen during 

 decay, but the depth of the color in scales varies considerably. Lar- 

 vae that die before the cells are sealed dry rapidly, and decay is 

 soon stopped; hence these scales are usually light colored. Larvae 

 that die after the cells are sealed usually become dark brown or 

 nearly black. Diagnosis of European foulbrood is more difficult 

 after the dead brood is decayed and dry. 



For a short time after death, larvae can be removed from the cells 

 without tearing the skin. Within a few days the skin and other 

 tissues become soft ; and the larvae settle against the lower wall of 

 the cells, and appear moist, melting, and flattened. At this stage 

 in decay, larvae are somewhat translucent and watery and cannot 

 be removed entire. Upon drying they become pasty, sometimes 

 ropy, and finally rubbery or brittle. Scales of European foulbrood 

 usually do not cling closely to the cell walls and are easy to remove. 



Larvae that die of European foulbrood in sealed cells may become 

 quite ropy and resemble larvae dead of American foulbrood. Since 

 the bees remove dead brood from open cells first, it sometimes hap- 

 pens after disease ceases to be active that the brood which died in 

 sealed cells is all that remains in the combs. When this happens it 

 may be difficult to tell whether American foulbrood, or European 

 foulbrood, or both of these diseases are present. 



ODOR OF DEAD BROOD 



The odors of European foulbrood cannot be accurately described 

 but must be learned by smelling of the dead brood. When there are 

 many decaying larvae in the combs an odor that is characteristic of 

 this disease can sometimes be detected. Usually the odor of recently 

 dead larvae is slight. A sour odor is sometimes present in partially 

 decayed larvae. Some larvae, particularly those that die after they 

 have straightened out and the cells are sealed, develop a putrid odor 

 resembling the odor of decayed meat. This odor is nearly always 

 present in larvae killed by European foulbrood which in other re- 

 spects resemble larvae killed by American foulbrood. After the 

 odors have been learned, the odor test helps considerably in dis- 

 tinguishing between European and American foulbrood when other 

 symptoms overlap, 



PARAFOULBROOD 

 CAUSE 



Parafoulbrood is caused by bacteria which resemble the bacteria 

 of European foulbrood. Worker, queen, and drone larvae and some- 

 times pupae are killed by the bacteria, which grow within the di- 

 gestive tract, but adult bees are not affected by this disease. The 

 spore stage of the bacterium found in affected brood is known as 

 Bacillus pa?*a-alvei. 



