Infestation dynamics and reinvasion of Varroa destructor mites in honey bee colonies kept isolated and in groups

Apidologie 32 (2001) 453–520


Experimental colonies were kept at a military training area and at a research station, neither of which was accessible to other beekeepers. The colonies were distributed as follows: (1) isolated colonies (no other colonies within a distance of 1.5 km; n = 9); (2) colonies in groups (two apiaries, each with three colonies); (3) control colonies, which were kept at distances between 1 and 800 m from an infested apiary and were continuously treated with a contact acaricide.

In all colonies, the numbers of honey bees and brood cells were evaluated at 3-week intervals (March–November) by the Liebefeld method, and samples of bees and brood were analyzed for V. destructor infestation. In March, infestations of between 100 and 1000 mites per colony were calculated. Mites on the bottom boards of the control colonies were counted at weekly intervals to record the mite invasion rate. The maximum infestation values were recorded in August with 7000–46000 mites per colony. The colonies were clearly damaged by this extreme V. destructor infestation, and only two colonies were able to overwinter.

*** The mite population dynamics were independent of the number of colonies kept in the same location (isolated vs. group colonies), and independent of the initial level of infestation (r2 = 0.06 ns). The majority of mites in the control colonies were observed in August and November. During this period, an average of 2150, 1300 and 1010 mites arrived in colonies directly in the apiary and in the colonies at distances of 300 and 800 m from the apiaries, respectively. The peak arrival of mites was correlated with the breakdown of infested colonies. An infestation rate of 100–1000 Varroa mites early in the year can, therefore, lead to the damage of colonies already in summer, independently of further invasion by V. destructor.

The rate of reinvasion increases significantly during the late season and cannot be effectively prevented by distances < 1 km between infested apiaries.

*** For good beekeeping practice, (1) a low initial infestation in spring; and (2) anti-V. destructor treatment of all colonies at the same time is required.