ISLE OF WIGHT DISEASE IN HIVE BEES— ACARINE DISEASE. 215 



II. Morphology, development, and habit.s all point to the fact that this is a 

 parasitic organism which must have been related to the tracheal .sy.stem of some 

 host for an indefinite period. The habit is not new. If T. woodi has been a 

 parasite of bees for ages, it seems improbable that the disease phenomena which 

 accompany its presence, and such as we are now familiar with, could have escaped 

 notice. On the other hand, it may be that, although the parasitic relationship is 

 not new. the pathology is. But such is not very probable. 



It is true that, as far us bee records go, there have been in the past periods of 

 epizootic disease in bees from time to time, but there is no evidence that a con- 

 tinuous epizootic extending from sixteen to eighteen years has taken place. 



III. It may be suggested that earlier methods of bee-keeping, whereby destruction 

 of bees was annually resorted to, kept down this parasite. This would certainly 

 liave been the case, if the parasite were present, and the method should be applied 

 to all existing diseased stocks before winter. But surely the disease would then, as 

 now, have manifested itself constantly in the working season to a degree sufficient 

 to attract attention. And it must be remembered that modern methods of bee- 

 keeping are not confined to Great Britain and Ireland. 



IV. May it not be that Tarsonemua, owing to some unknown change in the 

 normal balance of inter-relations, is at present undergoing one of those periods of 

 undue increase such as occurs from time to time in various animal forms. We must 

 recognise that it may be a parasite of bees which normally does not attain such an 

 incidence as to attract special notice, and that in recent times there has been some 

 change in the " balance of nature " which has led to its excessive increase. Bee- 

 keeping has increased in Britain within the last twenty-five years ; can it be said 

 that, apart from the ravages of this disease, our Islands are overstocked ? This 

 again is unlikely. 



V. It has been suggested that British bees of the present time are of a deterior- 

 ated breed, and have lost resisting power, so that Tarsonemus, a relatively non- 

 pathogenic parasite ordinarily, is able to breed excessively. My provisional answer 

 is that other racial forms are similarly affected. For example, Egyptian, Dutch, 

 Punic, and Italian bees can be readily infected, and in these Tarsonemus multiplies 

 with disastrous results, as in British bees. But the question of the ability of a stock 

 to survive a prolonged period of Tarsonemus infection is not a simple one ; amongst 

 other factors, it involves the question of relative fertility of particular queens, as 

 well as that of individual tolerance of the parasite (p. 191). 



VI. Tarsonemus may be relatively new to hive bees and normal to some other 

 insect. 



There remains the possibility that Tarsonemus exists normally in some wild 

 insect — possibly a hymenopteron — related to the hive bee, and that invasion of the 

 bee is recently established. In such a case, the unknown normal host will remain a 

 potential reservoir of the parasite. 



TRANS. ROY. SOC. EDIN., VOL. LII, PART IV (NO. 29). 120 



