214 DR JOHN RENNIE ON 



Reviewing the main features of T. ivoodi, it appears that there are good grounds 

 for regarding this as a species of specialised structure in relation to the particular 

 habitat in which it lives. 



Biological Considerations. 



I now propose briefly to consider the biological problem presented by T. ivoodi 

 in relation to Isle of Wight disease. 



For the final acceptance of the thesis that T. woodi is exclusively responsible 

 for the condition known as Isle of Wight disease, careful consideration must be 

 paid to the biological aspect of the problem. 



I. Although the numbers of bees examined from outside Great Britain in relation 

 to those from within have been comparatively few, yet considerable numbers have 

 been tested. Through the assistance of the Ministry of Agriculture, bees arriving 

 in this country accompanying queens from Italy have been obtained in a number of 

 cases for examination. 



In all, several hundreds of bees were obtained from this source. These, along 

 with others obtained direct from Italy, were searched for the presence of Tarsonenius. 

 The result of these examinations was that the bees were found entirely -free from 

 the parasite. The evidence is so far satisfactory that it may be accepted that 

 Tarsonemus is not being introduced to this country in Italian bees. Smaller 

 numbers of Dutch bees so imported have also yielded on examination a similar 

 result. Bees in limited numbers have also been obtained from Switzerland and from 

 North America, all of which were also free from this parasite. The evidence is not 

 complete by any means, but, as far as it goes, it is of one kind. Since this disease 

 has never been clearly demonstrated to exist outside the British Isles, nor certainlj'^ 

 any epizootic approaching in any way the dimensions of Isle of Wight disease in the 

 British Isles, and further, since all such evidence as we possess points to a causal 

 relation between Tarsonemus and Isle of Wight disease in bees, this coincidence in 

 distribution is noteworthy. If a geographical distribution limited to Britain should 

 be established in the hive bee — and to do this is a mere matter of time and favour- 

 able opportunity — in my opinion it would point to a relatively recent invasion of the 

 bee, although the opposite finding would not be against such a view. 



It may be noted that Zander (1911), who has paid particular attention to 

 the recording of pests found in hives and upon hive begs in Germany, makes no 

 reference to Acarids of any kind. In the course of our investigations we have found 

 in hives or upon combs, dead or live bees, at least five different species, including 

 one other species of Tarsonemus* These mites will be dealt with in a subsequent 

 publication. 



* In C. H. Acad. Paris, t. 62, 1866, M. Emil Duchemin records the occurrence of a microscopic Acarus on 

 diBeased liivo bees. He gives no description nor figure. This is clearly not an endoparasite, since M. Duchemin 

 found that it bred upon sunflowers protected from the bees. 



