Читать книгу Honey Bee Medicine for the Veterinary Practitioner - Группа авторов - Страница 33

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).