2.1. Taxonomy

Varroa mites were first discovered more than 100 years ago on the Asian honey bee (Apis cerana) in Java, Indonesia and named Varroa jacobsoni (Oudemans, 1904). They were assigned to a new genus, Varroa, and eventually to a new family, Varroidae (Delfinado-Baker and Baker, 1974). At present the genus contains four species.

Since the initial discovery, it has become clear that varroa mites are native brood parasites of a group of cavity nesting Asian honey bees that are closely related to A. cerana. These include, A. cerana itself (which is distributed throughout most of Asia), A. koschevnikovi (Borneo and surrounding regions), A. nigrocincta (Sulawesi) and A. nuluensis (Borneo).  These bees are still undergoing taxonomic revision as seen by the recent proposal to elevate the plains honey bee of south India to a new species, A. indica, and separate it from A. cerana (Lo et al., 2010). At present, varroa mites are only known to infest A. cerana, A. koschevnikovi and A. nigrocincta, although very few surveys for mites have been reported for A. nigrocincta, A. nuluensis or A. indica and those mites that have been found on A. nigrocincta in Sulawesi were most likely not native to that bee, but rather to sympatric A. cerana (Anderson and Trueman, 2000).

It is not exactly certain when the European honey bee (A. mellifera) first came in contact with varroa but it certainly occurred after that bee was introduced into Asia by man (De Jong et al., 1982). There are specimens of varroa in the Acarological Collection at Oregon State University, USA, that were collected from A. mellifera in China during the middle of the last century (Akratanakul and Burgett, 1975). The varroa mites that have since utilized A. mellifera as a host are all members of V. destructor, the most recently described species of the genus, and are native to A. cerana in northeast Asia (Anderson and Trueman, 2000). Hence, the current four recognized species of varroa came about through a long process of speciation on Asian honey bee hosts and, given the rather uncertain taxonomic status of those bees, it is possible that new varroa species await discovery. Prolonged co-evolution of V. destructor and A. mellifera many yet see these mites also becoming genetically diverse (Oldroyd, 1999), particularly as they gradually adapt to exist on isolated populations of A. mellifera. However, the movement of bee stocks around the world by man and the beekeeping practice of re-queening large numbers of A. mellifera colonies on a regular basis with queens from a common source will, to some extent, counter natural evolutionary processes that may eventually lead to varroa speciation on A. mellifera.

Various methods have been used over the years to determine variation within varroa, all of which have contributed to the current level of taxonomic understanding.  The most common and simple methods of identifying species have been those that provide measurements of mite physical characteristics (morphology). These methods are discussed below. The initial discoveries of V. jacobsoni on A. cerana, V. underwoodi on A. cerana and V. rindereri on A. koschevnikovi all resulted from morphological studies.

More recently, molecular methods have helped clarify varroa taxonomy and have proven particularly useful for identifying genetic variation within species and even identifying cryptic species. These methods, also described below, played a crucial role in the discovery of a new species, V. destructor, and in showing that it was that species, not V. jacobsoni as previously thought, that had colonized A. mellifera after its introduction into Asia (Anderson and Trueman, 2000).

The current taxonomy of varroa on Asian honey bees can be summarized as follows (after Lindquist et al., 2009):

Kingdom: Animalia

Phylum: Arthropoda

Class: Arachnida

Subclass: Acari

Superorder: Parasitiformes

Order: Mesostigmata

Family: Varroidae

Genus: Varroa

Species:

V. jacobsoni (Oudemans, 1904)

V. underwoodi (Delfinado-Baker and Aggarwal, 1987)

V. rindereri  (De-Guzman and Delfinado-Baker, 1996)

V. destructor (Anderson and Trueman, 2000).

The taxonomic status of three genetically distinct varroa types that infest A. cerana in the Philippines remains unresolved at this time (Anderson, 2000; Anderson and Trueman, 2000).

Mites of just two ‘haplogroups’ of V. destructor (see section 2.4.5. ‘Haplogroup and haplotype identification’) have colonized A. mellifera globally. Of the two, those belonging to a Korea haplogroup are the most common and widespread on A. mellifera, being present in Europe, the Middle East, Africa, Asia, the Americas and New Zealand. Mites of a Japan haplogroup are less common on A. mellifera, and are only found in Thailand, Japan and the Americas (Anderson and Trueman, 2000; Warrit et al., 2006). At the present time Australia remains the only large landmass on earth on which the resident A. mellifera are free of varroa.