Acarapis woodi
(honeybee mite)

Preferred Common Name

• honeybee mite

Other Scientific Names

• Tarsonemus woodi (Rennie, 1921)

International Common Names

• English: acarine mite; honey bee tracheal mite; internal mite; Tarsonemid mite; tracheal mite

Local Common Names

• Germany: Bienenmilbe; Honigbienenmilbe
• UK: acarine disease mite; Isle of Wight disease mite
• USA: honey bee mite

EPPO code

• ACASWO (Acarapis woodi)

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Chelicerata
•                 Class: Arachnida
•                     Subclass: Acari
•                         Superorder: Acariformes
•                             Suborder: Prostigmata
•                                 Family: Tarsonemidae
•                                     Genus: Acarapis
•                                         Species: Acarapis woodi

Acarapis is a genus of minute mites that are mainly parasitic on insects. A. woodi invades the tracheae of honey bees and is the cause of acarapisosis (OIE, 2012).

Morse and Eickwort (1990) reported that A. woodi may have evolved from an externally-dwelling species of Acarapis, possibly near the end of the nineteenth century in the UK. They suggest that evidence supporting this hypothesis includes: early severe infestations of acarine disease in the UK, followed by a rapid decline; the apparent absence of tracheal mites in honey bees in several European countries until many years after the initial discovery of the mite; the absence of tracheal mites in European honey bees in Australia, New Zealand, and (until 1984) North America; and great variability among North American honey bees regarding susceptibility to A. woodi.

A. woodi is included in a redescription of the genus Acarapis by Delfinado-Baker and Baker (1982).

Honey bee tracheal mites were first reported from dying bee colonies in the Isle of Wight, UK, in 1921 (Woodward and Quinn, 2011), although later evidence suggested that the “Isle of Wight” disease could not be attributed to the mites (Bailey, 1964, in Denmark et al., 2000). Widespread bee mortality was attributed to the mites in early twentieth-century Europe (Woodward and Quinn, 2011) and they were considered as important pests in the UK in the early 1920s (Bailey, 1985).

The mites were unknown in North America before 1980, when they were detected in Mexico, about 200 miles south of the border with the USA. They were first discovered in the USA in Hidalgo County, Texas in early July 1984. By August that year they were reported from Louisiana and by October they had been found in Florida, Nebraska, New York, North Dakota and South Dakota. Seventeen American states reported their presence by August of the following year, and they eventually spread to the rest of the country. Migratory beekeepers and commercial suppliers of bees facilitated their spread (Woodward and Quinn, 2011).

Once in a hive, the mites can move quickly through a colony via bee-to-bee contact. Workers and drones disperse them when moving from hive to hive; the mite is dispersed through entire apiaries or from one apiary to another (Woodward and Quinn, 2011).

The mites are invisible to the naked eye; the females are 143-147 microns long and 77-81 microns wide, in comparison to the males, which are 125-136 microns long and 60-70 microns wide. They have white oval bodies with a shiny, smooth cuticle. There are several long fine hairs on the body and legs, and the mouthparts are beak-like and elongated. (Woodward and Quinn, 2011).

Denmark et al. (2000) describe the species as follows:

‘Female: Length 140 to 175 microns, width 75 to 84 microns. Idiosoma ovoid or nearly pyriform; dorsal shield and plates faintly sclerotized, with indistinct punctures. Propodosoma lacking pseudostigmatic sensilla; two pairs of long, attenuate setae, verticals V1 and scapulars Sce. V1 setae shorter than Sce, about 1/4 longer than distance between bases of setae Sce. Ventral apodemes I forming Y-shaped structure with anterior median apodeme (a conspicuous transverse band crossing the thorax in front of the scutellum), not joining transverse apodeme. Apodemes III weakly extending lateral to bases of trochanters III. Apodemes IV extending to bases of trochanters IV. Posterior median apodeme rudimentary, sometimes as faintly formed Y- shaped structure. Leg 1 robust with single hooked claw. Legs II and III each with paired claws. Leg IV stubby, widely spaced; femur-genu and tibiotarsus functioning as one segment; tibiotarsus IV two times as long as broad; femur-genu broader than long, with three setae unequal length; tibiotarsus abruptly narrowed, almost straight, about two times as long as broad. For a more complete description see Delfinado-Baker and Baker (1984) [1982].

Male: Length 125 to 136 microns, width 60 to 77 microns. Similar to female except for sexual differences. Apodemes III to IV not developed, barely discernible. Posterior median apodeme indistinct, sometimes forming weak Y-shaped structure. Apodemes V present as weakened transverse apodeme barely discernible. Leg I more robust than others. Leg IV short, about 3/4 as long as leg III, without claw; trochanter large, slightly longer than wide, with seta; femur-genu slightly more than two times as long as wide, without flanges, three setae of unequal length; tibiotarsus nearly straight, slightly shorter than femur-genu; apical with slender pointed solenidion and 1 very long seta. Males and nymphs are difficult to separate from other known species.’

Beekeepers and commercial bee suppliers could suffer an economic impact due to A. woodi. Bee mortality caused by infestations of A. woodi varies; if infestations are high, mortality can be high and entire apiaries have reportedly been lost. In particular, when A. woodi was introduced to the USA, widespread losses of bee colonies and entire apiaries were reported. However, most honey bee colonies in the USA have developed some resistance to or tolerance of mite infestations and acarine disease is not as severe as it was in the 1980s and 1990s; the introduction of the varroa mite (Varroa destructor) in 1987 overshadowed the impact of A. woodi (Woodward and Quinn, 2011).

Honey bees are important to the agricultural and horticultural sectors as pollinators, so any disease causing decline in bee populations will have a significant impact on their role in these industries.

Impact on Habitats

Jyothi (2004) studied factors affecting pollinators, pollination and seed production of sunflowers in Karnataka, India during 1996-97. The aim of the study was to look at the effects of endosulfan and parasitic mites, including A. woodi, on Apis mellifera, Apis cerana, Apis florea, Apis dorsata and Trigona iridipennis (they also studied fly and butterfly pollinators). As well as reporting a significant decrease in seed yield and pollinator population after insecticide application, they also found a decrease in targets returning with pollen load at mite-infested colonies compared with normal colonies. Obviously factors affecting pollinators will also have an impact on pollination and thus ultimately affect an ecosystem that relies on pollination for development.

Impact on Biodiversity

A. woodi is listed as one of the causes of the decrease of honey bees in the world by Kadowaki (2010).

The effect of acarapisosis outbreaks on honeybee health will also have a significant impact on honey products and thus the livelihood of beekeepers.

• Proved invasive outside its native range
• Highly mobile locally

• Host damage
• Negatively impacts animal health
• Negatively impacts livelihoods
• Threat to/ loss of native species
• Negatively impacts trade/international relations

• Parasitism (incl. parasitoid)

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect as a commodity contaminant
• Difficult to identify/detect in the field
• Difficult/costly to control