The Occurrence of Diseases of Adult Bees, II. 3 



GENERIC NAME OF THE MITE. 



Dr. John Rennie, of the University of Aberdeen, Scotland, with 

 his associates, P. Bruce White and Miss Elsie J. Harvey, found in 

 1920 that this scourge is caused by a microscopically small parasitic 

 mite, 2 which was named Tarsonemus woodi (50). In this paper it 

 will be noted that in referring to reports from various authors the 

 generic names Acarapis and Tarsonemus are both used for this mite. 

 The name Tarsonemus woodi was given this mite by Rennie, and 

 Tarsonemus is still accepted by him as the correct generic name (17) . 

 Hirst (31, 32) believes that because of certain important structural 

 modifications, probably attributable to its parasitic habit, a new 

 genus, Acarapis, should be erected for it. It is coming to be rather 

 generally accepted that Hirst is correct, and his standing as a spe- 

 cialist in this field entitles his opinion to great Weight. The fact that 

 the generic name Acarapis is composed of two appropriate words, 

 "acarus" (a mite) and " apis " (the honeybee), makes it a fitting 

 name for this parasitic species, but in taxonomic nomenclature fitness 

 of the name argues neither for nor against its acceptance (25) . The 

 name Acarapis woodi is preferred by Dr. H. E. Ewing (25) , of this 

 bureau, specialist in mites, and by the writer (£8). 



An important paper on this subject by Vitzthum (70), the well- 

 known mite specialist of Germany, has recently appeared, in which 

 it is shown that the mite causing the Isle of Wight disease certainly 

 does not belong to the genus Tarsonemus, as claimed by Rennie, who 

 discovered it, but that it property belongs to the new genus, Acarapis, 

 erected by Hirst. Vitzthum states that while Acarapis is related to 

 the genus Tarsonemus, in that both genera belong to the Heterostig- 

 mata, it is more nearly related to certain other genera containing 

 mites parasitic on other insects. He points out that, in spite of the 

 fact that Acarapis contains the only known species of mites which 

 are internal parasites, the body form has not been materially modified 

 by the parasitic habit. This taxonomic analysis by Vitzthum seems 

 to settle conclusively the disputed question as to the correct generic 

 name for this species. 



ORIGIN OP THE PARASITIC HABIT. 



Since the recognition of the Isle of Wight disease there has been 

 much speculation among beekeepers as to how the parasite arose and 

 when and by what means it assumed its parasitic habit. There is, 

 of course, not the slightest reason to believe that this mite first in- 

 vaded the thoraxes of bees on the Isle of Wight in 1904, or that its 

 parasitic habit is a new one. From its specialized structure, one must 

 conclude that the parasite has existed as such for untold centuries 

 (cf. 50). It is an interesting speculation whether this mite took on 



2 Mites do not belong to the class of insects (Hexapoda), but are members of the class 

 of Arachnida, to which also belong spidersi and scorpions. A prominent difference be- 

 tween the two classes is the presence of four pairs of legs in the adult arachnids, instead 

 of three pairs as in insects. Mites (Acarina) are small animals some species of which 

 are found in great abundance. They generally have a saclike, unsegmented body, usually 

 fused with the cephalothorax, and the mouth parts form a beak. The abdomen and 

 cephalothorax are, however, distinct and the abdomen is segmented in the Tarsonemidae. 

 to which Acarapis woodi belongs. The larva on hatching from the egg usually has only 

 three pairs of legs, but after molting has four pairs as in most, adult mites. Most 

 species are free-living, as predacious forms or scavengers, but some species are parasitic 

 and cause certain plant diseases. Some animal diseases are properly attributed to this 

 group. Certain species are found in human ailments, such as itch. Acarapis woodi 

 seems to be the only described tarsonemid mite which is pathogenic on animals. 



