2.2.4. Life cycle
The life stages are, egg, larva, and adult. The nymphal instar remains inside the larval skin (Fig. 5). Males complete their development in 11 to 12 days, females in 14 to 15 days; therefore, a new generation of mites can emerge in two weeks (Pettis and Wilson, 1996). All stages of HBTM feed on bee haemolymph, which they obtain by piercing the walls of the trachea and air sacs with their sharply pointed stylets that move by internal chitinous levers (Hirschfelder and Sachs, 1952). Once the bee trachea is pierced, the mites’ mouth presses close to the wound and bee haemolymph is sucked through the short tube into the pharynx.
All mite instars live within the tracheae and associated air sacs (Figs. 5, 6, 7, 8), except during a brief period when adult, mated females disperse to search for young (generally less than four days old) bee hosts. Mites are attracted to the outflowing air from the prothoracic spiracle and to specific hydrocarbons from the bees’ cuticle (Phelan et al., 1991; McMullan et al., 2010) and immature stages may move into the trachea via air currents during bee respiration (Ochoa et al., 2005). HBTM females are less attracted to older bees, which during the summer will usually not live long enough for the mites to complete their life cycle.
Fig. 5. Life cycle of tracheal mites. (Morse, 1991).
Fig. 6. A. Pro-thoracic trachea of a honey bee, filled with HBTM; B. Micrograph of stained tracheal tubes with mites (left) and clean, no mites (right) (Photos: D Sammataro, Light Stereoscope 400×); C. LT-SEM micrograph of an open tracheal tube showing female, male and immature mites and eggs. Note the smaller males further inside the trachea, arrowed (Photo: E Erbe and R Ochoa).
Fig. 7. A. View of interior of tracheal tube containing a female HBTM; the long setae on Leg IV are thought to be used to help measure the interior walls of tracheae (Ochoa et al., 2005); B. Larval mite (arrow), adults and egg (far right). (LT-SEM photos: E Erbe and R Ochoa).
Fig. 8. A female tracheal mite questing on bee seta. Drawing: D Sammataro (Sammataro and Avitabile, 2011).