Honey Bee Medicine for the Veterinary Practitioner. Группа авторов
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transfer of pathogens or parasites from one colony to another horizontally can occur by four main routes: drifting, robbing, contact while foraging, and shared use of a contaminated environment. Drifting occurs when a forager enters another colony by accident, something that is largely a byproduct of modern apiary management since the wide spacing of wild colonies largely precludes drifting (Seeley 2017b; Seeley and Smith 2015). Robbing occurs primarily during periods of a nectar dearth, when strong colonies attempt rob honey from weak ones. In this case, pathogen transfer is most likely to occur from the weak colony to the strong colony, though the opposite is also possible. The transfer of pathogens during contact while foraging has been described in both natural and experimental models, including video documentation of a Varroa mite jumping onto a foraging honey bee the instant the bee lands on a flower (Peck et al. 2016). Finally, diseases can be spread from one colony to another through sharing of contaminated water, as has been observed with infections of the microsporidium Nosema apis (L'Arrivée 1965).
Honey Bee Demographic Turnover
In the article entitled, What epidemiology can teach us about honey bee health management, Delaplane (2017) reviewed the ecological and evolutionary impacts of the host–parasite relationship and proposed that an important driver of virulence is the high rate of introduction of susceptible colonies into apiaries (i.e. the introduction of new individuals into existing populations). Epidemiologists recognize three distinct “compartments” for individuals in a population exposed to a disease: Susceptible (S), Infected (I), and Recovered (R) individuals. In the simplest SIR (Susceptible, Infected, and Recovered) model, once susceptible animals catch the disease they become members of the infected “compartment” and can spread the disease to susceptible individuals. The infected animals that survive then move into the recovered “compartment” and are considered immune for life (Kermack and McKendrick 1927). Delaplane argues that the beekeeping practice of restocking “dead‐out” hives with nucleus colonies prolongs the epidemic by introducing new “S” individuals into the population of colonies in an apiary, a process that fosters the evolution of virulence (Fries and Camazine 2001). In a closed population, however, a disease epidemic is not artificially prolonged and the surviving individuals tend to have resistance, so there tends to be coevolution of the host–parasite or host–pathogen relationship. Given the high levels of colony losses experienced by beekeepers each year, the restocking of colonies with “nuc” replacements – thereby introducing a fresh batch of susceptible individuals to the apiary population – may represent one of the most noteworthy (and easy to address) management practices contributing to the collapse of honey bee colonies (Cornman et al. 2012).
Now let us return to those curious observations of populations of mite‐surviving honey bee colonies in various places around the world. A common thread among these reports of populations of honey bee colonies surviving Varroa infestation for long periods without the use of miticides is the isolation of these populations of colonies from managed colonies. The colonies live on islands (Gotland Island in Sweden or the island of Fernando de Noronha off the coast of Brazil), in remote inaccessible regions (far‐eastern Russia), or in an intact forest ecosystem (the Arnot Forest in the northeastern United States). The isolation from managed colonies found in all three of these scenarios must have favored the evolution of avirulence of Varroa and the multitude of viral diseases vectored by this mite. In essence, these populations all lack an important feature that drives virulence of infectious disease – a steady introduction of “S” individuals. With no new “Susceptible” colonies coming into these populations, in each case the mites and the bees have co‐evolved a stable host–parasite relationship. In the case of the Arnot Forest bees, we know the Varroa invasion was associated with significant loss of genetic diversity in the bees (an indicator of heavy colony mortality caused by Varroa), but at the same time the surviving colonies of this population possessed effective defenses against the mites (Mikheyev et al. 2015; Seeley 2017b).
It is here that the “good lifestyle” of colonies occupying small nest cavities, living widely spaced, and swarming frequently meets the “good genes” of colonies that are living as an isolated “island” of colonies. Now that we have married the good genes and the good lifestyle aspects of health in our examination of honey bee management, where does the bee doctor fit into this picture? In the final section of our chapter, we will explore how we can use the knowledge garnered from a deep understanding of wild colonies to develop a new way of keeping healthy colonies in managed apiaries, an approach recently named Darwinian beekeeping (Seeley 2017a).
Lessons from the Wild Bees
Modern apiarists practice pest/disease control, close colony spacing, swarm control, queen rearing, mating control (sometimes), annual requeening of colonies, migratory beekeeping, queen imports, drone reduction, and various other alterations of the bee's natural biology. These apiculture practices tend to limit natural selection and to disrupt the hard‐won adaptations of A. mellifera; they impact both the genes and the lifestyle of the honey bee (Neumann and Blacquière 2016). Now, what can be done from an animal husbandry and animal health perspective to reverse such trends?
The bee doctor must be prepared to examine honey bee health through a new lens that takes a holistic approach to medicine – one that features an understanding of and appreciation for the health of honey bees living in nature. In some parts of the world, beekeepers are already looking at beekeeping less as a process of domestication that forces the production of honey, wax, propolis, and pollination at great cost to colonies and more as the stewardship of a natural living system. The global decline in bee health is a direct consequence of man's disruption of this system: the introduction of exotic parasites and pathogens, the rise in disease virulence driven by beekeeping practices, and the evolution of drug resistance caused by indiscriminate treatments of colonies. Indeed, it is the pharmaceutical‐centric approach to preventative care for honey bees that is the fundamental reason behind the inclusion of honey bees among the food‐producing animals in North America that now fall under FDA regulations requiring the services of a veterinarian for antibiotic use. A key feature of a healthy system is achieving a balance between the host and the pathogen that promotes host resistance and pathogen avirulence – we can find this balance by promoting good genes and a good lifestyle in the bees.
Figure 1.7 Polyandry, or the multiple matings of a queen with drones from different patrilines, has been associated with colony vigor and improved winter survival. The health benefits of polyandry are linked to improved foraging rates, greater brood production, lower mite infestations, and the possession of rare alleles important for control of infectious disease.
Promoting Good Genes
The idea that honey bees have been domesticated by mankind remains a matter of debate. What is clear is that across North America there are populations of wild colonies of A. mellifera that thrive independent of beekeeping activities and that do not require the regular input of new colonies from honey bee swarms arising from managed colonies (Oliver 2014; Seeley 2017b; Radcliffe and Seeley 2018). Furthermore, the wild colonies tend to be genetically distinct from those that queen breeders produce for commercial purposes; the former are both more diverse genetically and they show strong evidence of regional adaptation (Figure 1.7) (reviewed in Seeley 2019a,b). Evidently, the honey bee colonies managed by beekeepers are semi‐domesticated, since their genes are influenced somewhat by queen breeders and their lifestyle is strongly influenced by their owners (Chapman et al. 2008; Oliver 2014).
An important lesson can be learned from the many animals that man has domesticated over the past thousand years: domestication carries with it a reliance on humans and generally a loss of the ability to survive in the wild. Here we can take some guidance from Charles Darwin: