The Occurrence of Diseases of Adult Bees, II. 5 



Hennie (52) has repeatedly seen the female mites on the outside of 

 infested bees, where they have apparently migrated after mating. 

 The mites live but a short time away from their hosts or after the 

 death of the bees, usually not more than 24 hours. 



CAUSE OF SYMPTOMS. 



The manner m which these parasites injure their hosts and cause 

 the Isle of Wight disease is also not entirely clear (59, 3 If). In- 

 ability to fly, so common in advanced cases of the Isle of Wight 

 disease, may be produced by artificial stopping of the spiracles of 

 the thorax (59), so that "crawlers," so frequently found in badly 

 infested colonies, may result from mere mechanical shutting off of 

 the air which passes into the tracheal trunks. Mites are often so 

 numerous as to make the passage of air virtually impossible. The 

 muscles of flight are located immediately adjacent to the trachea? 

 which are invaded, and an infinite number of small tracheal 

 branches permeate this musculature (56) , so that it may be assumed 

 that the stoppage of these trunks would affect the aeration of the 

 flight muscles, and possibly also that of the head, before any other 

 portion of the bee's body would be affected by this mechanical stop- 

 page. This would seem adequate explanation of the lack of power to 

 fly so frequently seen in advanced stages of the Isle of Wight dis- 

 ease, but since the same symptom is seen in bees affected with 

 other diseases of adult bees, this makes the mechanical explanation 

 less certain. The so-called bee paralysis and Nosema disease, both 

 found in the United States, are not caused by this mite and the 

 tracheae of bees suffering from either of these diseases are clean. In 

 addition to the puncturing of the tracheal walls to suck the blood 

 of the host and the stopping of air circulation, there is believed to 

 be (59) some change in adjacent tissues. It is also assumed that 

 these parasites may produce some material which has a toxic effect 

 on the host, but this does not appear certain. The way in which the 

 symptoms of this disease are produced seems to be a question of 

 theoretical interest only, since, regardless of its method, this mite ob- 

 viously causes the Isle of Wight disease, and therefore the control 

 of the disease must rest on the elimination of the mites. 



SYMPTOMS. 



The symptom most commonly observed in a colony suffering from 

 a severe attack of the Isle of Wight disease is that many bees crawl 

 inactively on the ground in front of the hive, unable to fly. They are 

 frequently seen falling from the alighting board to the ground or 

 in cool weather gathered in little clusters on the ground in front of 

 the hive. Such bees usually fail to return to the hive and die of 

 hunger or exposure, probably usually of hunger, since active bees in 

 summer live without food for only a few hours. The wings are 

 sometimes carried in a position abnormal for walking bees, with the 

 front and hind wings neither hooked together nor lying flat on the 

 dorsal surface, often described as " dislocated.'' The badly infested 

 bees in the spring are usually heavily laden with feces, probably 

 because of their inability to fly during winter. _ Doubtless because 

 of this accumulation of feces, attention was first given the alimentary 

 tract as the probable location of the cause of the disease (29, J^6). 



