2.2.5. Mite dispersal

Once a suitable host is found (queens, workers or drones), the female mite enters a trachea via the spiracle to lay eggs. Drones have been found to have more mites than workers (Royce and Rossignol, 1991; Dawicke et al., 1992), perhaps due to their larger tracheal trunks. Workers, however, which are more abundant through the year, are the prime host and reservoir for HBTM in bee colonies. Queens, even those commercially reared, often have HBTM. Camazine et al. (1998) found that infested queens weighed less, however, queens with completely black thoracic tracheae have been observed laying eggs and otherwise acting normally (D Sammataro, pers. obs.). Mites will also infest the air sacs of the bees’ abdomen and head (Giordani, 1965), and can be found externally at the base of the bee’s wings (Royce and Rossignol, 1991); the fate of the mites found in these areas and their effect on the host is unknown.

Female mites can disperse when the host bee is more than 12 days old, peaking at 15 to 25 days by questing on bee setae (Pettis and Wilson, 1996; Fig. 8); mites have a higher dispersal rate at night (Pettis et al., 1992). Eggs and female HBTM have been found at the wingbase of the bee’s thorax (Royce et al., 1988). During this questing period, mites are vulnerable to desiccation and starvation, and their survival depends on the ambient temperature and humidity (Giordani, 1962). An exposed mite will die after a few hours unless it enters a host; they are also at risk of being dislodged during bee flight and grooming (Sammataro and Needham, 1996; Sammataro et al., 2000). In infested and crowded tracheal tubes, males move about and locate pharate nymphal females that are about to moult to adulthood and guard them in advance of mating (Ochoa et al., 2005). The males do not attach to the immature stages as is common in other genera in the family Tarsonemidae (Ochoa et al., 2005). Only the female HBTM go deep into the tracheal system, measuring the walls of the tracheal branches with their dorsal and ventral setae and the leg IV seta; see Fig. 7A (Ochoa et al., 2005). The eggs are 5 to 15 µm longer than the adult females (see Fig. 7B).

The genotype of honey bees and the location of the colonies influence the levels of HBTM infestations. Buckfast, ARS-Y-C-1 (Yugoslavian) and Russian honey bees are known to be resistant to HBTM (Lin et al., 1996; Danka et al., 1995; de Guzman et al., 2002, 2005). Heat is also associated with mite mortality (Harbo, 1993). Exposing hives to direct sun impedes HBTM mite population growth and shading them tends to accelerate it (L. de Guzman, unpub. data).