248 



pajasite may thereby be regarded as clean. Where 

 mites are being imported into a stock, e.g., by robbers, 

 or in other cases of recent invasion, practically all of 

 the infestations consist of single females and their 

 young brood. They are almost invariably situated in 

 the primary tracheae close to the spiracles. Unless the 

 dissection Ls properly performed the initial portion of 

 the respiratory tube is very liable to be lost. Such an 

 error may prevent the detection of the disease at its 

 very beginnings, when control measures can be most 

 effective. 



III. Not only is it necessary that every case of in- 

 festation in the sample should be noted, but it is further 

 imperative that different degrees of this within the stock 

 should be separately estimated. It has been found 

 useful, for example, where a prognosis is aimed at, to 

 recognise three degrees of infestation, viz. : — 



(a) Recent. Shown by the healthy condition of the 

 tracheae, the number of mites, which in this case is 

 generally limited — ^total of all stages 10 or fewer, — and 

 their situation — usually confined to the primary tracheal 

 trunk below the first forking. 



(h) Well-established, This is shown by the presence 

 of larger numbers of mites of all stages, the more ex- 

 tensive occupation of the tracheae, which may or may 

 not show bronzing or deterioration. Infestation of both 

 sides of the body may be a feature in a proportion 

 of these cases. Perhaps the best criterion of this stage 

 is the clear evidence of breeding in active progress. 



(c) Old infestation. The most obvious feature here 

 is the greatly bronzed or actually blackened condition 

 of the tracheae, with obliteration of their original 

 structure. The number of living mites is noticeably 

 fewer, or these may be absent. Dead mites are not un- 

 common in such cases, and bees may be found which, 

 having well marked indications of a previous infestation, 

 now show no mites at all. Dead mites, it should be 

 borne in mind, may be found at any of the stages 

 indicated by these three grades. 



The relative proportions of each of these stages in a 

 sample, or the preponderance of any one of them, are 

 factors to be taken as a guide in prognosis regarding a 

 stock. 



