Swarming in honey bees (Apis mellifera) and Varroa destructor population development in Sweden

Abstract

-In a honey bee population of 150 colonies, the development of an introduced Varroa destructor mite population was monitored in swarming and non-swarming colonies for two years in a Nordic climate. The results demonstrated a reduced mite population as a result of swarming only for the first swarm season studied. In the second swarm season, there were much higher mite levels (based on debris counts of mites) and fewer colonies swarmed, but there was no significant difference in infestation levels of adult bees in the fall between swarming and non-swarming colonies. This result was interpreted as an effect of host-parasite interactions, where the detrimental influence from the infestation prohibited growth (and swarming) in some colonies, but allowed better mite reproduction opportunities (and swarming) in others. Surprisingly, the mite infestation levels of swarms in the late fall were not significantly different from those of swarming colonies the same year, indicating that swarm survival may be almost as much affected by V. destructor, as intact, swarming colonies. No horizontal mite transfer through robbing was observed. The results suggest that, horizontal mite transfer may not be as important in a Nordic climate where many bee colonies die over winter along with their mites, as it is in warmer climates.Varroa destructor / Apis mellifera / swarming / survival / nordic climate / population dynamics

Natural Varroa mite-surviving Apis mellifera honeybee populations

“…The colonies came from a variety of locations around Sweden and included a diversity of honeybee races (Fries et al 2003). The experimental purpose was to evaluate if Varroa mites would eradicate the population under Nordic conditions without mite control treatments.…”

“…The experimental purpose was to evaluate if Varroa mites would eradicate the population under Nordic conditions without mite control treatments. The colonies were artificially infested with equal amounts of Varroa mites, were unmanaged, and free to swarm (Fries et al 2003).…”

“…Within the first 3 years, more than 80 % of the colonies died due to the rapid buildup of mite infestations (Fries et al 2003). Many colonies swarmed during the first 2 years, but by the third year, swarming decreased since colonies were too weak (Fries et al 2003).…”

“…Within the first 3 years, more than 80 % of the colonies died due to the rapid buildup of mite infestations (Fries et al 2003). Many colonies swarmed during the first 2 years, but by the third year, swarming decreased since colonies were too weak (Fries et al 2003). After the initial losses, the autumn mite infestation rates decreased, winter mortality decreased, and the incidence of swarming increased again as colonies recovered (Fries et al 2006).…”

The influence of genetic origin and its interaction with environmental effects on the survival ofApis mellifera L.colonies in Europe

“…Although neither of these factors was found to be statistically significant, both may have contributed to extending the duration of survival. Indeed, swarming has been shown to have an effect on mite infestation levels and, consequently, on colony survival (Fries et al, 2003).…”