endoparasites of honey bees; feed on hemolymph in tracheae and air sacs
Adult: Metapodosomal venter with 2 pairs of setae (3a, 3b) (3c, 4b absent) (Figs. 2, 4). No setae between trochanters IV (4b absent) (Figs. 2, 4). Seta pl’’ absent from tarsus I (Figs. 1, 3). Solenidion on tibia I present (Figs. 1, 3). Cheliceral stylets long, nearly straight, extruding from gnathosomal capsule anteriorly (Figs. 2, 3).
A dichotomous key is available in Delfinado-Baker and Baker, 1982b.
This genus is associated with honey bees Apis mellifera, Apis cerana, and Apis dorsata. Acarapis woodi (Rennie, 1921) has been found on all three of these bee species. Acarapis externus Morgenthaler in Morison, 1931 has been found on Apis mellifera and Apis cerana, and Acarapis dorsalis Morgenthaler, 1934 has been found only on Apis mellifera.
associated exclusively with bees or their close relative, wasps; cannot live without these hosts
some life stages are associated with bees, while others are not
can complete entire life cycle without bees or their close relative, wasps
Acarapis woodi mites are usually found in the large tracheal tubes of the mesosoma (Figs. 6, 7). (Detection of the mites requires dissection of the bees.) Development and mating take place in the tracheae and newly mated females migrate from the tracheae of their original host to tracheae in a newly emerged young adult bee. Host-seeking mites attach themselves to bee hairs and then move onto younger bees. Clustering of bees during the winter greatly facilitates cross-infestation. Mite males are seldom found outside the tracheae. Females lay a single large egg at a time, probably one egg per day during the first two weeks of the host's life. The egg hatches into an active feeding larva. Nymphs are pharate, developing inside the larval skin. Adults emerge about 11 days after oviposition. This pattern of development is similar to that of other tarsonemid mites.
Acarapis woodi mites pierce the bee tracheae and air sacs with their chelicerae and feed on the hemolymph, possibly impairing bee respiration. This lowers the bee's ability to use wing muscles. As a consequence, bees cannot keep their cluster warm in winter. Overwintering bees die when crawling out of colonies. In warmer climates, bees will survive, but the mites can pass on harmful viruses. The mite also can weaken drones and queens.
Acarapis woodi is responsible for significant colony losses throughout North America. Reports of losses as great as 90% have been recorded. A heavy mite load causes diminished brood area, smaller bee populations, looser winter clusters, increased honey consumption, lower honey yields, and, ultimately, colony demise. In temperate regions, mite populations increase during winter, when bees are confined to the hive (making it easier for mites to move between bee hosts), and decrease in summer when bee populations are highest. In subtropical climates, the cycle is similar, even though bees are not so confined (after Royce, 1999; Sammataro et al., 2000).
Two other species, Acarapis dorsalis and A. externus, are found on the European honey bee Apis mellifera, and they also feed on the bee hemolymph (Delfinado-Baker and Baker, 1982b).