28 CIRCULAR 3 9 2, U. S. DEPARTMENT OF AGRICULTURE 



die outside, When large numbers of infested bees crawl from the 

 hive at about the same time, the condition is known as mass crawling. 

 Bees often continue to work for weeks after they have become 

 infested by mites, and acarine disease may be well advanced in a 

 colony before, symptoms are noticeable. The most commonly rec- 

 ognized symptoms are crawling and the loss of ability to fly. Crawl- 

 ing may come on gradually when the disease spreads slowly within 

 the colony, or it may develop rapidly and result in mass crawling. 

 After mass crawling has occurred, the colony is freed of most of 

 the diseased bees and may appear to recover temporarily. Mass 

 crawling often folloATs a period of unfavorable weather. Crawling 

 is frequently accompanied by retention of feces, swollen abdomens, 

 and un jointed wings. 



Figure 18. — Acarine disease. Discolored trachea taken from the thorax of an infested 

 bee. The mites that cause acarine disease can be seen through the tracheal wall. Mag- 

 nified 75 times. (Photograph by J. Rennie.) 



DIAGNOSIS IN THE APIARY 



In healthy bees the tracheae are always pure white. In heavily 

 infested bees the tracheae become bronzed or blackened in irregular 

 spots. The presence of these spots is used as a symptom in diagnosis. 

 With the aid of a lens that magnifies 6 or 8 times, the dark-colored 

 spots can be distinguished. They may be few in number, or there 

 may be so many that the trachea appears black (fig. 18). 



In making examinations for acarine disease in the apiary it is best 

 to use crawlers. The tracheae of bees killed by other disorders often 



