Читать книгу Honey Bee Medicine for the Veterinary Practitioner - Группа авторов - Страница 31

In honey bees, one way that a colony achieves reproductive success is by swarming: an established colony casts a swarm to produce a new colony. The other way that a colony achieves reproductive success is by producing drones; even though weak colonies can propagate their genes by producing drones, this does not create another colony. If a pathogen or parasite that is transmitted vertically (from parent to offspring) weakens its host and so hampers it from producing offspring (which for honey bee colonies equates to casting swarms) then it reduces its own reproductive success. In short, the natural mode of colony reproduction in honey bees favors the evolution of avirulence in most of its pathogens and parasites. The two exceptions to this generalization are American foulbrood and Varroa destructor, both of which are easily transmitted horizontally when one colony robs honey from another.

Swarming also helps inhibit the reproduction of Varroa mites (and other agents of brood diseases) by creating a natural break in brood production, which forces the mites to likewise suspend their reproduction (Seeley 2017b). Once a daughter queen emerges to replace the mother queen that has left in a swarm, this daughter queen must leave the hive to fly to a drone congregation area, where she will mate with multiple drones before returning to the hive to commence egg laying. This transition from mother queen to daughter queen creates a period without sealed brood (needed for mite reproduction) that can last from 7 to 14 days. This imposes a break in the reproduction of the Varroa mites. Furthermore, with each swarming event a sizable fraction (approximately a third) of the colony's mite population is exported with the departing workforce: the fraction of mites shed can be readily calculated since about half of the female breeding‐age mites are on the workers in a colony at any given time, and nearly three‐quarters of these workers depart in the prime swarm (Rangel and Seeley 2012). In a six‐year study of the life‐histories of wild honey bee colonies living in a forest in the northeast US, Seeley (2017b) found that most (~87%) swarmed each summer.

In contrast to the relatively small nest cavities of wild honey bee colonies, the colonies kept by beekeepers occupy large hives, and they are less apt to produce swarms (Oliver 2015). The swarm control methods of beekeepers include transferring sealed brood to the top of the hive and queen exclusion (the Demaree method), cutting out queen cells, preventing the filling of cells around the brood nest with nectar (possibly a cue for swarming) by providing empty combs above the brood nest, reversing the brood boxes and inserting empty combs in the brood nest, and reducing the worker populations of colonies by splitting them. All of these methods weaken the stimuli that trigger swarming, but only one helps control the Varroa mites: the removal of bees. We propose instead controlled colony fission by making “splits” to mimic the beneficial effects of swarming on mite control (Loftus et al. 2016).