776 
DR JOHN RENNIE ON 
Reviewing the main features 'of T. woodi, 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. woodi 
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 Tarsonemus. 
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 certainly 
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 bees 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 G. R. Acad. Paris , t. 62, 1866, M. Emil Duchemin records the occurrence of a microscopic Acarus on 
diseased hive 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. 
