g6 Mites Injurious to Domestic Animals. 



that the metabolic products of the mite may perhaps cause toxaemia 

 (see " Bee World," October, 1920 April, 1921, p. 59). White has 

 pointed out that pathological changes take place in the tubes 

 infested by them ; whilst the muscles concerned with flight also show 

 degenerative changes. The tracheal tubes of bees are normally pale, 



FIG. 79. 



Acarapis woodi. Female from above, x 405. 

 (After Hirst, Ann. Mag. Nat. Hist., June, 1921.) 



but in advanced cases of the disease they become brownish or 

 blackish, and this makes it easy to recognise the malady, for if the 

 tracheae of a bee are discoloured the mite is invariably present. This 

 change in the colour of the tracheal tubes is accompanied by hardness 

 and brittleness of their walls. White has shown that if one of the 

 thoracic stigmatal openings of a bee is closed with wax, the insect loses 



