2.1. Taxonomy

Honey bee tracheal mites were first described by Rennie as Tarsonemus woodi in 1921, as parasites of the Western (European) honey bee Apis mellifera  L. This discovery followed extensive colony mortality on the Isle of Wight and elsewhere in the UK between 1904 and 1919 when bee colonies began to die from unknown causes (Rennie, 1921). The initial suspicion that the “Isle of Wight Disease” was caused by tracheal mites (Hirst, 1921; Rennie, 1921) was never confirmed (Bailey, 1964). Hirst (1921) reclassified the species as Acarapis woodi, the name by which it is known today (Lindquist, 1986). Its detection led to the restriction of all live honey bee imports into the USA in 1922 (Phillips, 1923). Despite this, the first report of colony losses from HBTM in the USA came from beekeepers in Texas in 1984. Thereafter, A. woodi spread to all states of the USA and most Canadian provinces. Their range expansion was facilitated by commercial beekeepers transporting bees for pollination, and from the sale of mite-infested package bees.

In addition to A. woodi, there are two external mite species in the genus Acarapis that infest honey bees. A. externus  Morgenthaler is found on the cervix (the neck region) and A. dorsalis  Morgenthaler is found on the dorsal groove of the thorax (Ibay and Burgett, 1989; Fig. 1. A, B; Table 1). They were considered to be harmless by Eckert (1961) and Delfinado-Baker (1984), but that may reflect a lack of information on these two Acarapis species.  A third external species, A. vagans (Schneider), described from central Europe and New Zealand, was found principally on drones, on the basal part of the hind wing (Lindquist, 1986). However, other researchers considered this species to be nomen dubium and to date this issue has not been resolved (Delfinado-Baker and Baker, 1982; Lindquist, 1986).

Unfortunately, HBTM is now overshadowed by the ectoparasitic mite, Varroa destructor Anderson and Trueman. As a result, the presence of HBTM in some instances is not regularly investigated. When found, they are often at very low levels, perhaps due to the treatments used to control V. destructor (see Dietemann et al., 2013).

The current taxonomy of HBTM, based on Krantz et al. (2009) is:

Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Aranea
Subclass: Acari
Superorder: Acariformes
Cohort: Heterostigmatina
Superfamily: Tarsonemoidea
Family: Tarsonemidae
Genus: Acarapis
Species:
A. woodi (Rennie)
A. dorsalis Morgenthaler
A. externus Morgenthaler
A. vagans (Schneider)

Fig. 1. A. Ventral view of Acarapis dorsalis (ex. New Zealand honey bee); B. A. externus (ex. New Zealand honey bee) and; C. A. woodi adult female (ex. Canadian honey bee) taken at a 400x magnification under light microscopy. (Photos: Dr Qing-Hai Fan).

figure1

Table 1. Differential diagnosis of Acarapis species (Ritter, 1996).

Character

A. dorsalis

A. externus

A. woodi

Notch of the coxal plate

Deep

Short

Flat

Space between stigmata

16.7 µm

16.8 µm

13.9 µm

Length of tarsal limb (IV leg pair)

7.6 µm

11.4 µm

7.5 µm