ON ISLE OF WIGHT DISEASE IN HIVE BEES — ETIOLOGY. 
741 
Cumulative Evidence that Tarsonemus is Causally Belated 
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 Bennie and Harvey on the dates mentioned 
(see p. 752). 
Keputed 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 — eg. 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. 
