16 Department Circular 287, U. S. Dept. of Agriculture. 



related to the Isle of Wight disease or identical with Acarapis 

 woodi. This mite is identified with a considerable degree of cer- 

 tainty by Vitzthum (58) as a migratory nymph of THchotarsus 

 osmiae. Several species of mites have been found on honeybees and 

 in and about beehives (11, 16, 4-3, 50), and it is important that such 

 mites shall not be confused, through careless identifications, with 

 the one species known to be pathogenic to honeybees. 



SWITZERLAND. 



Since the announcement of the discovery of the cause of the Isle 

 of Wight disease in 1920, the investigators of the Schweizerische 

 Bakteriologischen Anstalt at Liebefeld, near Bern, and the apiary 

 inspectors have been watching for Acarapis woodi in that country. 

 The investigation of bee diseases for Switzerland is carried on in 

 that laboratory, under the direction of Prof. Robert Burri, whose 

 work on the brood diseases of bees is well and favorably known. 



During the year 1921 examinations were made of adult bees that 

 were suspected of disease or which showed any abnormality, but no 

 specimens of Acarapis icoodi were found (40). It is now known, 

 however, that the mite was present in Switzerland before that time 

 (U). On February 1, 1922, Dr. Otto Morgenthaler (41) of the 

 station found dead mites, later identified by Rennie and himself as 

 Tarsonemus icoodi, on the outside of bees that had died during the 

 winter, no evidence of disease having been noted previously. He 

 then found that mites of this species, or at any rate indistinguishable 

 by microscopic examination, were present on similar dead bees ob- 

 tained by him from five towns in Switzerland ( u wherever I looked 

 for it "). This finding of the mite on the outside of dead bees which 

 had not shown any definite signs of disease led to speculation as to 

 the possibility that Acarapis icoodi is in Switzerland a harmless 

 symbiote of the honeybee : that it lives with the bees without either 

 species being injured by the mutual adaptations. In an English 

 review (IS) of the above-mentioned paper this view is suggested, 

 following a less definite suggestion of the same nature by Morgen- 

 thaler himself. In reply to this review Morgenthaler (J$) states, 

 however, that this does not correctly reproduce his view and that 

 he considered the mites found on the outside of dead bees as dead 

 animals (parasites) which had left their hosts on the death of the 

 hosts. 



In the same numbers of the two Swiss bee journals in which the 

 report of the unsuccessful search in 1921 appeared, there was pub- 

 lished a note by Morgenthaler (40) reporting that two specimens of 

 diseased bees had been examined in cases in which definite symptoms 

 of disease had been noted. This indicates that the Isle of Wight 

 disease as it is found in Great Britain is actually found in Switzer- 

 land, and precludes the belief that Acarapis woodi is in Switzerland 

 always a harmless symbiote. The development of the work in 

 Switzerland on this mite and on the conditions in the colonies which 

 it produces have added materially to our knowledge of the subject, 

 and while there is still much to learn it is becoming more and more 

 evident that this mite is to be considered a serious pest of the apiary 

 in Switzerland and elsewhere, wherever it is found. 



In a later article (4$) Morgenthaler summarizes the information 

 on Tarsonemus woodi, gives various reports of the finding of mites 



