ON ISLE OF WIGHT DISEASE IN HIVE. BEES— ETIOLOGY. 741 



Cumulative Evidence that Tarsonemus is Causally Related 



TO THIS Disease. 



In the course of our investigation we have searched over three thousand individual 

 bees representing 250 separate stocks scattered throughout Great Britain. These 

 examinations covered over 110 stocks reported to us by reliable bee-keepers or certi- 

 fied by ourselves as suffering from Isle of Wight disease. The parasite was present 

 in every one of those stocks. A striking result of this part of the inquiry, which 

 involved the examination individually of 700 bees at least, was the discovery that in 

 every case showing the familiar symptoms of Isle of Wight disease the parasite was 

 present. No exception has been found. There is apparently an invariable and clear 

 association of this organism with all bees suffering from Isle of Wight disease. 



These examinations applied not only to bees obtained during 1920, but included 

 samples representative of all seasons of the year, and dating back as far as September 

 1916. These observations relating to the earlier dated bees were made upon diseased 

 bees which had been preserved by Rennib and Harvey on the dates mentioned 

 (see p. 752). 



Reputed Healthy Stocks. 



Amongst the 250 stocks above mentioned there were about 50 which were 

 reported to us as healthy and in which we found the parasite Tarsonemus to be 

 present. That is to say, of 140 stocks believed by the owners to be healthy, 50, or 

 nearly 36 per cent., harboured this parasite. Concurrent with such discoveries 

 we ascertained by direct examination ourselves of flying bees (l) which were 

 members of colonies in which the disease was definitely established and (2) which 

 were taken from colonies believed to be healthy and showing no indications otherwise, 

 that amongst these were to be found considerable numbers harbouring the parasite. 

 This was further complicated by the fact that in those infected flying bees certain of 

 those pathological conditions — e.g. the blackening and hardening of the tracheal 

 tubes — were very marked. As an example it may be quoted that this condition was 

 found in bees entering the hive carrying pollen or nectar, both belonging to stocks in 

 which crawling and other symptoms were well established, and also to those reputed 

 healthy stocks. 



A Particular Case. 



As an illustration of this aspect of the disease we may quote the following : — 

 At the door of the hive of a sick stock showing habitual crawling in fine weather 

 and steadily declining from the disease, we captured as they alighted 27 foraging 

 bees in the course of a single afternoon. Tarsonemus was found in every one of these 

 bees, all stages of development being represented. In a number of the cases, soiling 

 and destruction of the tracheal tubes was very marked, quite as bad as anything we 

 have observed in bees crawling from the disease. 



