738 DR JOHN RENNIE, MR PHILIP BRUCE WHITE, AND MISS ELSIE J. HARVEY 
exhibits, however, totally different external symptoms and a distinct pathology in 
the individual bee. Collateral work by G. F. White (1918) in America supports 
this latter conclusion. The problem of the cause of Isle of Wight disease until now 
has thus been left unsolved. 
Characteristics of the Disease as Hitherto Observed in the 
Colony as a Whole. 
The diagnosis of Isle of Wight disease from “ symptoms ” has always been a more 
or less unsatisfactory procedure. Hitherto the presence of the disease in a colony 
has not been recognised until infection has been well advanced in a high proportion 
of the bees. At this stage of disability, the most usual features recognisable by the 
bee-keeper are inability to fly, accompanied sometimes with imperfect folding of the 
wings. In fine weather a proportion of the affected bees may leave the hive and 
crawl around, climbing grasses, etc. Later, in the cooler part of the day, they 
commonly collect in small clusters. Such bees are lost to the colony, since they do 
not return to the hive, and in any case are useless as workers at this stage. Some- 
times large numbers come out and loiter on the alighting board in the sun, returning 
to the hive when the sun has gone. Associated with the incapacity for flight there 
is- usually a congested condition of the colon. In certain circumstances dysentery 
may be present as a complication. Most of these symptoms may be present in 
other disorders of a more temporary kind, and we have been accustomed to regard 
as true Isle of Wight disease only those cases where such visible conditions, once 
commenced, continued in the stock, affecting succeeding broods of bees. There is a 
continuous mortality from the disease. Bijllamore and Malden regard no single 
symptom as characteristic, and state that “ the only essential feature is the death of 
large numbers of bees.” 
The association of the causative organism now to be considered will henceforth 
afford an exact means of diagnosing the disease, which we suggest should now be 
designated Acarine disease. 
Discovery of the Causal Agent of Isle of Wight Disease. 
The present and following papers announce the discovery of a parasitic organism 
invading the respiratory system of the adult bee, which after exhaustive investiga- 
tion we now bring forward as the causal agent in this disease. This parasite is a 
hitherto undescribed mite, identified by one of us (J. R.) as belonging to the genus 
Tarsonemus. It was first observed by one of us (E. H.) in December 1919, when 
a single example was found in a portion of trachea present in a preparation, per- 
manently preserved, of the thoracic glands (fig. l). # It was significant of the fuller 
knowledge of the disease, soon to be attained, that the bee in which it occurred was 
* This find was followed up at the time by a systematic search for mites in hives, upon frames, bees, etc., which 
resulted in the finding of no fewer than five different species in definite association with bees, dead and alive. (J. R.) 
