358 Scientific Proceedings, Royal Dublin Society. 



especially hampered by the difficulty in obtaining diseased bees. We must 

 take this opportunity of thanking the Minister of Agriculture, Mr. Hogan, and 

 some of the officials of the Depai'tment of Agriculture for the interest they 

 have taken in our work and for the loan of some pamphlets. 



For the benefit of those not especially acquainted with the subject, the 

 following simple account is given : — 



In the higher organism, like man, the function of bringing oxygen for 

 respiration to the tissues and cells, as is well known, is carried out by the 

 blood, but among certain of the animal groups, one of which contains the 

 bees, there is found instead a separate sj'stem of air-tubes or tracheae which 

 ramify or branch over the tissues carrying oxygen to the cells. Any blockage 

 of these air-tul)es brings partial or total asphyxia to the tissues served by the 

 blocked tube, just as stoppage of a blood-vessel going to a part of the body 

 would produce a like change. 



Biologists have never ceased to wonder at the powers which exist in the 

 thoracic-wing muscles of insects; the rapidity with which these muscles are 

 able to operate, and their endurance are alike remarkable. The air-tubes or 

 tracheae which serve these thoracic muscles with oxygen are the seat of the 

 disease under discussion. The mite or acarid crawls in through the external 

 opening of the tube or stigma, and breeds rapidly within the lumen of the 

 trachea. In later stages the bees are unable to fly, and crawl about the hive 

 or on objects near by : now bees only defecate when in flight, and consequently 

 the "crawlers" retain their foecal matter. This naturally led the earlier 

 investigators to consider that they were dealing with some complaint of the 

 alimentary canal, and no one seems to have thought of a connexion between 

 the state of the gut and a cause of the inability to use the wings. Thus the 

 discoveiy of the acarids within the air-tubes has proved a remarkable one. 



Reference to the microphotographs will give a good idea of the disease. 

 In PI. XVIII, fig. 1, is a photo of the adult male mite; it has four ijairs of legs, 

 with the piercing organs, palps, and chelicerae between the first two pairs. These 

 mites are verj' slow walkers, and are una.l)le to Yva\ like many of the free 

 living acarids. In PL XIX, fig. 7, is a photo of the upper part of one of the 

 tlioraeic tracheae; there is a main stem below, which brandies to form a Y, from 

 the upper i^art of which smaller air-tubes branch off, and finally form exceed- 

 ingly fine twigs that carry air to the tissues. In PL XVIII, fig. 4, is another 

 tube showing a branching lower down. The end on the left below d connects 

 to the exterior by the air-pore or stigma. In PL XVIII, fig. 3, the lowermost 

 part of the thoracic trachea is shown. 



The mother mite crawls into the tracheal tube through the stigma, and 

 generally comes to rest just inside. In PL XVIII, fig. 2, is a clean tube 

 flattened under the cover-slip and photographed ; in fig. 3 is a tube which 

 shows the first stage of infection. The mother mite at ? has already laid two 

 eggs, V- and I- ; in PL XIX, fig. 5, the familj^ has increased, and the mites are 

 woi'king their way up the tube; while in fig. fi the infection is heavy, and 

 the female mites at ? have been breeding rapidly. Some time after the tube 

 or trachea becomes infected another fact may be noted : in PL XVIII, fig. 4, 

 is shown very clearly, at dd, a black smudge on the wall of the tube. This 

 smudge is caused by the mites, and eventually spreads in large patches and 

 areas, and finally the tube becomes blackened, as shown in PL XIX, fig. 8. 

 Such bees are doomed, and are unable to fly, or at all events to fly far. 



The mite is believed to feed by sucking the haemocoel or body cavity (or 

 blood) fluid of the bee which surrounds these tubes, so that the mites, by 

 pricking through the wall with their chelicerae are able to draw fluid for 



