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II.-THE PROGRESS OF INFESTATION. 



(a) Within the Bee. 



When the trachea of a bee is invaded by a female 

 mite, egg laying commences very commonly quite close 

 to the stigma. Cases of invasion may be observed 

 in which the only occupants of the trachea are a 

 female, along with an egg or eggs and unhatched larvae. 

 This points to the fact that the immigrant female is 

 already mated. I have observed many instances of 

 infestations at the initial stage, but have never found 

 males alone in such cases. When the conditions under 

 which development is taking place are realised, the 

 diflSculty of obtaining exact information on such points 

 as the length of life of a mite, the number of eggs pro- 

 duced by a single female, the total progeny of a single 

 invasion, what determines migration of certain females 

 and non-migration of others, and many other related 

 problems, will be readily appreciated. To most of 

 these questions I have no positive answer, as yet. In 

 a series of examples in which the infestation may be 

 described as definitely established, but in which migra- 

 tion had probably not commenced, I found the mites in 

 all stages to number from 49 to 18. In these cases the 

 adult females were never more than four, nor fewer 

 than three. A crude deduction which may be accepted 

 provisionally from such observations, gives us an 

 average from 5 to 10 offspring from each adult. The 

 following stages occur in the course of the complete 

 life-history, viz : egg, six-legged larva, immature un- 

 mated adult, fertile adult of both sexes. 



(b) Within the Hive. 



From Bee to Bee. 



As the mites bred within the bee increase in number 

 and attain maturity, they pass to the outside of the 

 bee, where by suitable methods of examination they 

 may be found creeping amongst or clinging to the hairy 

 covering. So far as we have been able to find out only 

 the adult female migrates in this way. When bees 



