239 



The result is inevitably unfavourable. Either the 

 stock does not survive the winter, or it does so having 

 a high proportion of infested and weakened bees. 

 While this is so, my observations show that the actual 

 rate of spread is slower in winter than in summer. I 

 account for this by the fact that in winter movements 

 amongst the bees of the cluster are limited and the 

 opportunities of transference of mites from one host to 

 another are correspondingly restricted. The fact that 

 the mortality from Aoarine disease is frequently less in 

 winter than in summer is possibly also due to the con- 

 stitution of the winter bee, whose normal longevity is 

 greater than that of summer. Also, much of the summer 

 mortality is accelerated by the bees leaving the hive 

 as " crawlers." 



Racial Vigour. 



Since infection with Tarsonemus woodi in the majority 

 of cases does not for some time incapacitate the bee, 

 the practical measure of the harmfulness of infection 

 lies in the extent to which it shortens the working 

 period of the bee's life. It will thus be seen that the 

 comparative vigour of different strains and also the 

 standard of health maintained are important elements 

 in enabling the members of a stock to bear the strain 

 imposed upon them by the presence of mites breeding 

 within their bodies and feeding upon their blood. The 

 breeding of robust bees, well adapted in constitution 

 to our climate and its foraging possibilities will pay in 

 relation to this disease as in other aspects of beekeeping. 



The term immunity is sometimes heard applied to 

 bees in connection with Acarine Disease. Simply in- 

 terpreted this term means capacity to withstand 

 infection. It may be as well to point out to those who 

 speak and write regarding races of bees which may or 

 may not be immune to Acarine disease that we have no 

 evidence of any kind that there exists a race or races 

 of hive bees in which Tarsonemus woodi could not 

 breed. It appears to me that until by controlled 

 mating and artificial selection the scientifically trained 

 bee expert can breed a bee whose thoracic spiracles are 

 too small to admit Tarsonemus to the respiratory 

 system — and this is a long way off — it is only confusing 



