Una súplica para el uso de la resistencia natural de las abejas en la apicultura

se discute en el foro de Dee un muy interesante artículo en la revista de apicultura americana „Bee World“

Una súplica para el uso de la resistencia natural de las abejas en la apicultura

A Plea for Use of Honey Bees’ Natural Resilience in Beekeeping

Aquí se trata de que las abejas antes cuando vivieron todavía salvajes, demostraron una potencia muy alta en relación con todo tipo de enfermedades y parásitos. Y ahora ha cambiado bruscamente en las últimas décadas.

Ahora recientemente, un estudio científico demostró que la reina puede agregar Immunprimers específicos a los huevos. Este primer se dirige a parásitos específicos, con quien la reina tuvo contacto. Este mecanismo inmune trabaja a través de la proteína vitelogenina y puede ser considerado análogo a la „vacunación“ de los descendientes. Obviamente, esta inmunidad heredada pierde la mayor parte de sus beneficios si se sustituye una reina.

Esto significa que la cria artificial de reinas está absolutamente cuestionable.

Allí está escrito:

The original traits of the honey bees provide a high level of resilience towards all kinds of diseases and parasites, which allowed beekeepers to keep the bees without the use of veterinary drugs. While in some countries diseases are still handled without medication, the situation has changed drastically with the arrival of the varroa mite in Europe. Varroa is a foreign exotic parasite, against which our honey bees had no defense. Unfortunately, as long as we do control the varroa mites in our colonies, there is no selection pressure left, and no resistance will ever evolve: the bees remain as vulnerable as they were upon arrival of varroa.

Recently, a study by Salmela, Amdam, and Freitak showed that the queen could add specific immune primers to eggs. These primers target specific parasites with which the queen has been in contact. This immune mechanism works through the yolk protein vitellogenin and can be considered as an analogue to “vaccination” of the offspring. This inherited immunity obviously loses most of its benefits when a queen is displaced, (beekeeper mediated queen replacement operations) as a native daughter queen would probably already be better adapted, through her mother’s primers and her exposure to the local disease variants, than to the disease variants of a mating station or those of a new colony

y Dee escribe que todo depende en la calidad de la jalea real con que las reinas son alimentadas por las abejas.

Dee Lusy escribió:Tienen que hablar con estas personas por que la jalea real con que se alimenta la reina tiene mucho que ver con esto cómo ella responde y pone huevos, y lo saludable que son las abejas por la composición de la jalea que se alimenta a ella. Y la descendencia es determinado por el tamaño de la celdilla como se publicó anteriormente en otros papeles publicados y nada nuevo, excepto para la nueva generación que viene ahora… no saber los antecedentes de nuestras abejas y que daño provocó el movimiento „más grande es mejor“ a las abejas.

 

Dee Lusy escribió:You need to talk to these people as the royal jelly the queen is fed has much to do with this for how she responds and lays eggs, and how healthy the bees are for the composition of the jelly fed to her and offspring is determined by the size of the cell with honey bees as written about earlier in other published papers and nothing new, except to new generation coming on now….not knowing past history of our bees and what done to them with bigger is better movement.

Journal

Bee World

Volume 95, 2018 – Issue 2

 

A Plea for Use of Honey Bees’ Natural Resilience in Beekeeping

Pages 34-38 | Published online: 17 Apr 2018

In this article

  • Honey Bees are Endemic
  • The Honey Bee is a Wild Species
  • Understanding: Resistance or Tolerance to Varroa is Required
  • How Does Resilience Work in Nature?
  • Conditions to be Met for the Evolution of a Balanced Host Parasite Relationship
  • Reproduction of Colonies: Vertical or Horizontal Transmission of Parasites?
  • Introduction of a New Queen: Vertical or Horizontal Transmission of Parasites?
  • Some Examples of Beekeepers Counteracting Honey Bee Colonies
  • Summary
  • Suggested Reading and Acknowledgements
  • References

This plea is about leaving room for nature in ordinary daily beekeeping, but also about leaving room for nature in the reproduction of the bee colonies, i.e. beekeeping without queen breeding and without cultivation of breeds. Our European honey bees (Apis mellifera) naturally possess numerous traits including behaviors that make them less vulnerable to diseases and other threats in their environment (Evans & Spivak, 2010 Evans, J.D., & Spivak, M. (2010). Socialized medicine: Individual and communal disease barriers in honey bees. Journal of Invertebrate Pathology, 103, S62S72.10.1016/j.jip.2009.06.019[Crossref], [PubMed], [Web of Science ®][Google Scholar]; Wilson-Rich, Spivak, Fefferman, & Starks, 2009 Wilson-Rich, N., Spivak, M., Fefferman, N.H., & Starks, P.T. (2009). Genetic, individual, and group facilitation of disease resistance in insect societies. Annual Review of Entomology, 54, 405423.10.1146/annurev.ento.53.103106.093301[Crossref], [PubMed], [Web of Science ®][Google Scholar]). It is very important for these properties to be retained in their full genetic width, in order to sustain the colonies’ capacities to continuously adapt to new conditions (Neumann & Blacquière, 2017 Neumann, P., & Blacquière, T. (2017). The Darwin cure for apiculture? Natural selection and managed honey bee health. Evolutionary Applications, 10, 226230.10.1111/eva.2017.10.issue-3[Crossref], [PubMed], [Web of Science ®][Google Scholar]). It is also important that we, as beekeepers, utilize as much as possible these adaptive abilities of the bees (Seeley, 2017a Seeley, T.D. (2017a). Darwinian beekeeping: An evolutionary approach to apiculture. American Bee Journal, 2017, 277282. [Google Scholar]). This means that it may occasionally be better to follow the bees’ nature rather than to force the bees to meet our requirements (Brosi, Delaplane, Boots, & de Roode, 2017 Brosi, B.J., Delaplane, K.S., Boots, M., & de Roode, J.C. (2017). Ecological and evolutionary approaches to managing honey bee disease. Nature Ecology & Evolution, 1, 12501262.10.1038/s41559-017-0246-z[Crossref], [PubMed], [Web of Science ®][Google Scholar]). Here we present several examples to underpin this statement.

Honey Bees are Endemic

Our honey bee occurs naturally as a wild species in Africa, the Middle East and Europe. Within this wide range, many described subspecies are present and well adapted to local circumstances. Additionally, there is variation within the different subspecies and the bees turn out to be strongly adapted to local conditions on a finer scale. Such local adaptation of “ecotypes” may be adaptation to the weather, to conditions and seasonality of forage, but also to local variation in diseases. A nice example is the “Landes” bee, a regional honey bee within the subspecies “black bee” (A. m. mellifera), adapted to the climate and forage conditions of an area in Les Landes, France (Strange, Garnery, & Sheppard, 2007 Strange, J.P., Garnery, L., & Sheppard, W.S. (2007). Persistence of the Landes ecotype of Apis mellifera mellifera in southwest France: Confirmation of a locally adaptive annual brood cycle trait. Apidologie, 38, 259267.10.1051/apido:2007012[Crossref], [Web of Science ®][Google Scholar]). A few native European subspecies were carried across seas as Europeans settled in new territories such as the Americas, Australia and Asia. By accident, man has also caused the spread of the African Savannah Bee (A. m. scutellata) in South, Middle and even North America (Africanized bees, sometimes called “killer bees”).

The black honey bee (A. m. mellifera) is the indigenous subspecies in our West European environment, with a distribution ranging from the Pyrenees through Western Europe (including the British Isles) far into Russia (De la Rúa, Jaffé, Dall’Olio, Muñoz, & Serrano, 2010 De la Rúa, P., Jaffé, R., Dall’Olio, R., Muñoz, I., & Serrano, J. (2010). Biodiversity, conservation and current threats to European honey bees. Review. Apidologie, 40, 263284.[Crossref], [Web of Science ®][Google Scholar]). However, beekeepers have introduced for centuries Italian (A.m. ligustica), Carniolan (A. m. carnica) and Caucasian (A.m. caucasica) queens to bring in qualities thought to be better suited for beekeeping (Meixner et al., 2010 Meixner, M.D., Costa, C., Kryger, P., Hatjina, F., Bouga, M., Ivanova, E., & Büchler, R. (2010). Conserving diversity and vitality for honey bee breeding. Journal of Apicultural Research, 49, 8592.10.3896/IBRA.1.49.1.12[Taylor & Francis Online], [Web of Science ®][Google Scholar]). As a result, our Western European black honey bee has been repeatedly hybridized with other subspecies. More recently, Buckfast bees also introduced properties (genes, actually alleles) of other honey bee subspecies (African and Middle East subspecies).

The Honey Bee is a Wild Species

Even though they have long been held by humans, honey bees remain a principally wild species (Oldroyd, 2012 Oldroyd, B.P. (2012). Domestication of honey bees was associated with expansion of genetic diversity. Molecular Ecology, 21, 44094411.10.1111/j.1365-294X.2012.05641.x[Crossref], [PubMed], [Web of Science ®][Google Scholar]). While in some countries there are efforts to select and breed honey bees, in many others, bees have hardly been domesticated or have not been domesticated at all. Where there are no active breeding and selection effort, the bees could be considered a wild species. Where more intensive selection and breeding occurs, we don’t have the level of domestication of farm animals, but we have semi-domestication, where some attributes of domestication coexist with some attributes of being a wild species. One could for instance perceive the situation in the USA as a case of domestication, where a handful queen breeders supply the whole continent with queens. For true “domestication” however, a prerequisite is the control of the organisms’ mating and reproduction by man, as it is the case in our livestock. The honey bee queens’ promiscuous mating behavior with more than 15 drones (polyandry) makes the domestication task difficult, unless by using artificial insemination or mating on isolated mating stations, for instance on islands. In addition, this mating with many drones (with ample genetic variation) is also necessary to build a well-functioning colony. There appears to be no difference in the number of drones with which a queen mates between wild and managed colonies (Tarpy, Delaney, & Seeley, 2015 Tarpy, D.R., Delaney, D.A., & Seeley, T.D. (2015). Mating frequencies of honey bee queens (Apis mellifera L.) in a population of feral colonies in the northeastern United States. PLOS ONE, 10(3), e0118734. doi:10.1371/journal.pone.0118734[Crossref], [PubMed], [Web of Science ®][Google Scholar]), in both cases about 15 to 22. This number of mating events is probably a compromise that yields sufficient genetic diversity, weighed against the risk taken by the queen with each additional mating, and therefore naturally selected as an optimum.

A queen mating on a station with 20 drones originating from a number of “drone-colonies”, headed by sister queens, might still run short in genetic variation. The drones might genetically be too similar, and due to this lack of variation the worker bees in the colony would also become too similar. A lack of some essential alleles of immunity-related genes might arise, resulting in a reduced ability to handle pathogens of the entire colony. A recent study (Delaplane, Pietravalle, Brown, & Budge, 2015 Delaplane, K.S., Pietravalle, S., Brown, M.A., & Budge, G.E. (2015). Honey bee colonies headed by hyperpolyandrous queens have improved brood rearing efficiency and lower infestation rates of parasitic varroa mites. PLOS ONE, 10(12), e0142985. doi:10.1371/journal.pone.0142985[Crossref], [PubMed], [Web of Science ®][Google Scholar]) showed that mating with much higher numbers of drones using artificial insemination (as this would not be achievable naturally) increased the resilience of the colonies to the varroa mite. Fifteen to twenty drones might be enough for most traits, but in some cases useful alleles might be so rare that 15–20 unrelated drones, or alternatively far more than 20 mating events are needed to come across those rare alleles.

It appears that, as soon as a selective breeding for desired properties such as gentleness, low swarming tendency etc. is stopped, these traits are quickly lost. This suggests that several man selected traits are not directly beneficial to the colony fitness, as they would remain frequent in the gene pool otherwise.

The original traits of the honey bees provide a high level of resilience towards all kinds of diseases and parasites, which allowed beekeepers to keep the bees without the use of veterinary drugs. While in some countries diseases are still handled without medication, the situation has changed drastically with the arrival of the varroa mite in Europe. Varroa is a foreign exotic parasite, against which our honey bees had no defense. Unfortunately, as long as we do control the varroa mites in our colonies, there is no selection pressure left, and no resistance will ever evolve: the bees remain as vulnerable as they were upon arrival of varroa.

Understanding: Resistance or Tolerance to Varroa is Required

The majority of the beekeeping community is now aware of the idea that the solution for varroa must also be sought in the resistance and tolerance mechanisms of the bees. This could allow the return to an old-fashioned apiculture free of veterinary drugs. We now also know that the survival of honey bee populations with varroa is possible in nature and in beekeeping operations (Locke, 2016 Locke, B. (2016). Natural Varroa mite-surviving Apis mellifera honey bee populations. Apidologie, 47, 467482.10.1007/s13592-015-0412-8[Crossref], [Web of Science ®][Google Scholar]; further examples: Kefuss, Vanpoucke, Bolt, & Kefuss, 2015 Kefuss, J., Vanpoucke, J., Bolt, M., & Kefuss, C. (2015). Selection for resistance to Varroa destructor under commercial beekeeping conditions. Journal of Apicultural Research, 54, 563576.10.1080/00218839.2016.1160709[Taylor & Francis Online], [Web of Science ®][Google Scholar]; McMullan, 2018 McMullan, J. (2018). Adaptation in honey bee (Apis mellifera) colonies exhibiting tolerance to Varroa destructor in Ireland. Bee World, 95(2), 39–43. doi:10.1080/0005772X.2018.1431000[Taylor & Francis Online][Google Scholar]; Oddie, Dahle, & Neumann, 2017 Oddie, M.A.Y., Dahle, B., & Neumann, P. (2017). Norwegian honey bees surviving Varroa destructor mite infestations by means of natural selection. PeerJ, 5, e3956. doi:10.7717/Perj.3956[Crossref], [PubMed], [Web of Science ®][Google Scholar]; Panziera, van Langevelde, & Blacquière, 2017 Panziera, D., van Langevelde, F., & Blacquière, T. (2017). Varroa sensitive hygiene contributes to naturally selected varroa resistance in honey bees. Journal of Apicultural Research, 56, 635642.10.1080/00218839.2017.1351860[Taylor & Francis Online], [Web of Science ®][Google Scholar]), so beekeeping without controlling the mite is no longer an unworldly vision. Only the path to it is controversial: should we go the usual route of breeding and beekeeping (retaining the qualities appreciated by the beekeeper), or should we follow the bees in their hard struggle to survive “in nature”?

The two methods to select varroa resistance or tolerance are:

(1) Targeted selection: We seek and choose (select) properties that counteract the development of varroa, and breed them into our bee stocks. For example, it could be breeding for hygienic behavior against the varroa mite (VSH) (Leclercq, Pannebakker, Gengler, Nguyen, & Francis, 2017 Leclercq, G., Pannebakker, B., Gengler, N., Nguyen, B.K., & Francis, F. (2017). Drawbacks and benefits of hygienic behavior in honey bees (Apis mellifera L.): A review. Journal of Apicultural Research. doi:10.1080/00218839.2017.1327938[Taylor & Francis Online], [Web of Science ®][Google Scholar]; Wilson-Rich et al., 2009 Wilson-Rich, N., Spivak, M., Fefferman, N.H., & Starks, P.T. (2009). Genetic, individual, and group facilitation of disease resistance in insect societies. Annual Review of Entomology, 54, 405423.10.1146/annurev.ento.53.103106.093301[Crossref], [PubMed], [Web of Science ®][Google Scholar]), or grooming of mites (Pritchard, 2016 Pritchard, D.J. (2016). Grooming by honey bees as a component of varroa resistant behavior. Journal of Apicultural Research, 55, 3848.[Taylor & Francis Online], [Web of Science ®][Google Scholar]). Such breeding requires a highly coordinated approach and controlled mating of the queens with selected drones. At the same time, consideration can be given to preserving the desired characteristics of bees for beekeepers (Uzunov, Brascamp, & Büchler, 2017 Uzunov, A., Brascamp, E.W., & Büchler, R. (2017). The basic concept of honey bee breeding programs. Bee World, 94, 8487.10.1080/0005772X.2017.1345427[Taylor & Francis Online][Google Scholar]). This route has already been applied, sometimes with some success (Rosenkranz, Aumeier, & Ziegelmann, 2010 Rosenkranz, P., Aumeier, P., & Ziegelmann, B. (2010). Biology and control of Varroa destructor. Journal of Invertebrate Pathology, 103, S96S119.10.1016/j.jip.2009.07.016[Crossref], [PubMed], [Web of Science ®][Google Scholar]). This approach actually takes domestication further. In principle, this can be done on a large scale (where selected queens are made available to beekeepers), but it can also be done locally.
(2) ”Natural” selection: We no longer control the mite and thus leave the bee colonies to deal with this suddenly increased parasite pressure. Ideally this results in some kind of remise (most beekeepers would consider ideal an outcome where the bees “win”, but that option may be illusory): there is a balance between bees and mites (hosts and parasites), in which both can survive. This route has already proven to be successful several times in nature (Seeley 2007 Seeley, T.D. (2007). Honey bees of the Arnot Forest: A population of feral colonies persisting with Varroa destructor in the northeastern United States. Apidologie, 38, 1929.10.1051/apido:2006055[Crossref], [Web of Science ®][Google Scholar], 2017b Seeley, T.D. (2017b). Life-history traits of wild honey bee colonies living in forests around Ithaca, NY, USA. Apidologie. doi:10.1007/s13592-017-0519-1[Crossref][Google Scholar]) as well as starting from colonies initially managed by beekeepers (Fries, Imdorf, & Rosenkranz, 2006 Fries, I., Imdorf, A., & Rosenkranz, P. (2006). Survival of mite infested (Varroa destructor) honey bee (Apis mellifera) colonies in a Nordic climate. Apidologie, 37, 564570.10.1051/apido:2006031[Crossref], [Web of Science ®][Google Scholar]; Kefuss et al., 2015 Kefuss, J., Vanpoucke, J., Bolt, M., & Kefuss, C. (2015). Selection for resistance to Varroa destructor under commercial beekeeping conditions. Journal of Apicultural Research, 54, 563576.10.1080/00218839.2016.1160709[Taylor & Francis Online], [Web of Science ®][Google Scholar]; Le Conte et al., 2007 Le Conte, Y., de Vaublanc, G., Crauser, D., Jeanne, F., Rousselle, J.-C., & Bécard, J.-M. (2007). Honey bee colonies that have survived Varroa destructor. Apidologie, 38, 566572.10.1051/apido:2007040[Crossref], [Web of Science ®][Google Scholar]; Oddie et al., 2017 Oddie, M.A.Y., Dahle, B., & Neumann, P. (2017). Norwegian honey bees surviving Varroa destructor mite infestations by means of natural selection. PeerJ, 5, e3956. doi:10.7717/Perj.3956[Crossref], [PubMed], [Web of Science ®][Google Scholar]; Panziera et al., 2017 Panziera, D., van Langevelde, F., & Blacquière, T. (2017). Varroa sensitive hygiene contributes to naturally selected varroa resistance in honey bees. Journal of Apicultural Research, 56, 635642.10.1080/00218839.2017.1351860[Taylor & Francis Online], [Web of Science ®][Google Scholar]). We may be able to speak of de-domestication, which is named feralisation. This process should be allowed to occur at various locations (with local bee colonies and their mites). Using this approach will also result in bee populations of colonies well adapted to the local environment. Surprisingly, “natural selection” appears to be effective after only a few years of refraining from control of varroa. That the “natural” way of selection through only elimination of the non-fitting phenotypes can result in fast evolution in honey bees was underpinned by a recent study (Avalos et al., 2017 Avalos, A., Pan, H., Li, C., Acevedo-Gonzalez, J.P., Rendon, G., Fields, C.J., … Zhang, G. (2017). A soft selective sweep during rapid evolution of gentle behaviour in an Africanized honey bee. Nature. doi:10.1038/s41467-017-01800-0[Crossref], [Web of Science ®][Google Scholar]) in which defensive Africanized honey bees in Puerto Rico evolved docility in just a decade. This selective sweep was shown to be based on several loci.

In both approaches of selection, the process is continuous and actually never ends. In addition, conditions can change, new pests can occur. In the latter case, method 1 will be constrained to look for new resistance traits and start the selection and breeding process according to the new plague. In method 2, the new pest will increase the selection pressure and will raise new resistance mechanisms without deleting the already acquired adaptations. The feralisation in method 2 might result in the loss of colony traits considered as “beneficial beekeeping characteristics”. Obviously, feralisation does not grant the return of lost alleles in the genepool (Johnsson et al., 2016 Johnsson, M., Gering, E., Willis, P., Lopez, S., Van Dorp, L., Hellenthal, G., … Wright, D. (2016). Feralisation targets different genomic loci to domestication in the chicken. Nature Communications, 7, 12950. doi:10.1038/ncomms12950[Crossref], [PubMed], [Web of Science ®][Google Scholar]). This is an additional warning against the overuse of selective breeding and domestication in beekeeping practices. It is also an argument for the protection of local subspecies and ecotypes without too much interference by beekeeping.

Theoretically, honey bees could have become fully domesticated and would be unable to survive without human intervention. However, there are strong examples showing this is not the case in the USA (Seeley, 2017b Seeley, T.D. (2017b). Life-history traits of wild honey bee colonies living in forests around Ithaca, NY, USA. Apidologie. doi:10.1007/s13592-017-0519-1[Crossref][Google Scholar]), France (Kefuss et al., 2015 Kefuss, J., Vanpoucke, J., Bolt, M., & Kefuss, C. (2015). Selection for resistance to Varroa destructor under commercial beekeeping conditions. Journal of Apicultural Research, 54, 563576.10.1080/00218839.2016.1160709[Taylor & Francis Online], [Web of Science ®][Google Scholar]; Le Conte et al., 2007 Le Conte, Y., de Vaublanc, G., Crauser, D., Jeanne, F., Rousselle, J.-C., & Bécard, J.-M. (2007). Honey bee colonies that have survived Varroa destructor. Apidologie, 38, 566572.10.1051/apido:2007040[Crossref], [Web of Science ®][Google Scholar]), Ireland (McMullan, 2018 McMullan, J. (2018). Adaptation in honey bee (Apis mellifera) colonies exhibiting tolerance to Varroa destructor in Ireland. Bee World, 95(2), 39–43. doi:10.1080/0005772X.2018.1431000[Taylor & Francis Online][Google Scholar]), Netherlands (Panziera et al., 2017 Panziera, D., van Langevelde, F., & Blacquière, T. (2017). Varroa sensitive hygiene contributes to naturally selected varroa resistance in honey bees. Journal of Apicultural Research, 56, 635642.10.1080/00218839.2017.1351860[Taylor & Francis Online], [Web of Science ®][Google Scholar]), Sweden (Fries, Imdorf, et al., 2006 Fries, I., Imdorf, A., & Rosenkranz, P. (2006). Survival of mite infested (Varroa destructor) honey bee (Apis mellifera) colonies in a Nordic climate. Apidologie, 37, 564570.10.1051/apido:2006031[Crossref], [Web of Science ®][Google Scholar]). An important argument to support the idea that bees are able to survive without help is that, before and after varroa, the life expectancy of wild or feralised colonies was not affected: about five to six years for an established colony (Le Conte et al., 2007 Le Conte, Y., de Vaublanc, G., Crauser, D., Jeanne, F., Rousselle, J.-C., & Bécard, J.-M. (2007). Honey bee colonies that have survived Varroa destructor. Apidologie, 38, 566572.10.1051/apido:2007040[Crossref], [Web of Science ®][Google Scholar]; Seeley 2017b Seeley, T.D. (2017b). Life-history traits of wild honey bee colonies living in forests around Ithaca, NY, USA. Apidologie. doi:10.1007/s13592-017-0519-1[Crossref][Google Scholar]), which is also similar to the life expectancy (6.6 years) of wild colonies in Australia, where varroa mites are not present (Oldroyd, Thexton, Lawler, & Crozier, 1997 Oldroyd, B.P., Thexton, E.G., Lawler, S.H., & Crozier, R.H. (1997). Population demography of Australian feral bees (Apis mellifera). Oecologia, 111, 381387.10.1007/s004420050249[Crossref], [PubMed], [Web of Science ®][Google Scholar]).

The importance of aligning as much as possible with what would happen in nature is crucial for method 2. Hence, let the bees make the most of their own potential in the fight against diseases. A simple example: while bees themselves prevent robbery and thus prevent entry of diseases by active guard bees, the beekeeper should not spread diseases from one colony to another by using, for example, contaminated beekeeping tools. As conspicuous as it seems, many widely accepted and used beekeeping methods counteract honey bees’ own resilience strategies.

How Does Resilience Work in Nature?

The theory, almost always verified by empirical data, predicts that invasive parasites cause much damage at the beginning of invasion as the host has not adapted yet to this new threat. But too virulent parasites take the risk of killing their host too quickly, therefore eliminating chances of transmission and leading to their own extinction. On one hand, hosts unable to cope with the parasite burden are killed without reproducing. On the other hand, stronger hosts effectively pass on their genes to the next generation, thereby favoring resistant or tolerant phenotypes in the population. Thus, as time and generations go by, both phenomena lead to a milder virulence of the parasite and a higher resistance or tolerance of the host (Schmid-Hempel, 2011 Schmid-Hempel, P. (2011). Evolutionary parasitology: The integrated study of infections, immunology, ecology, and genetics. Oxford: Oxford University Press. [Google Scholar]). In regular beekeeping many management measures as well as the choice of selected queens increase horizontal transmission paths and offend the development of a balanced mild host parasite relationship (Brosi et al., 2017 Brosi, B.J., Delaplane, K.S., Boots, M., & de Roode, J.C. (2017). Ecological and evolutionary approaches to managing honey bee disease. Nature Ecology & Evolution, 1, 12501262.10.1038/s41559-017-0246-z[Crossref], [PubMed], [Web of Science ®][Google Scholar]).

The host may develop both resistance (the ability to limit parasite burden) and tolerance (the ability to limit the damage caused by a given parasite burden, for example by becoming insensitive to a poison of the parasite, for definitions see Raberg, Graham, & Read, 2009 Raberg, L., Graham, A.L., & Read, A.F. (2009). Decomposing health: Tolerance and resistance to parasites in animals. Philosophical Transactions of the Royal Society B, 364(1513), 3749.10.1098/rstb.2008.0184[Crossref], [PubMed], [Web of Science ®][Google Scholar]). Both mechanisms can be deployed simultaneously and depend on the presence of the parasite. As long as beekeepers control the varroa mites, no balanced natural relationship can be maintained or arise between the mite and the bees.

Conditions to be Met for the Evolution of a Balanced Host Parasite Relationship

A parasite can be transmitted horizontally or vertically. Horizontal transmission is from one bee to another bee of the same generation, or from one colony to another colony. Vertical transmission means from mother to her offspring, for example through the eggs. Transmission of parasites from the mother colony to an after-swarm is a form of vertical transmission (the after-swarm is a daughter of the original mother-colony). With vertical transmission, adaptations to the parasite, in the genes that the mother passes along to her offspring, will be taken to the next generation (= the same colony with the new queen). There is a good chance that the colony with the daughter queen can handle the transmitted parasite better, as they are already acquainted. Parasites depend on their hosts’ survival or on successful transmission to other susceptible hosts. Therefore, when a parasite depends solely on vertical transmission, a mild virulence is crucial.

Reproduction of Colonies: Vertical or Horizontal Transmission of Parasites?

The natural reproduction of honey bee colonies is achieved through the process of swarming in spring. The prime swarm with the old queen with a part of the workers and drones forms the continuation of the original colony, with the “old” parasites and the already existing “relationship” between them. The remaining colony is now led by a new young queen and can be qualified as “new” or “daughter” colony. After the swarm leaves, the original parasites are still present but the genetic identity of the colony slowly changes as the workforce is replaced. Thus, there is a vertical transmission of the parasite (from mother (-colony) to descendant (colony)). The daughter inherited her mother’s properties (genes), allowing her and her offspring to deal with the parasite that her mother was able to handle. The colony also inherits genes from the drones that fertilized the queen, which will mostly have originated from other colonies. This new genetic identity, partly inherited and partly acquired might increase the fitness of the colony. The relationship between host and parasite might differ between the mother and the daughter colony, for good or bad.

The situation is similar for the sisters of the young queen which may leave the original colony in after swarms: if they succeed to build a balanced enough relationship, they may survive, if they fail they will die.

The swarm (both prime and secondary swarms) loses or escapes part of the parasites with which the colony “had a relationship”, since parasites of the brood do not or barely go with a swarm (Paenibacillus larvae, Fries, Lindström, & Korpela, 2006 Fries, I., Lindström, A., & Korpela, S. (2006). Vertical transmission of American foulbrood (Paenibacillus larvae) in honey bees (Apis mellifera). Veterinary Microbiology, 114, 269274.10.1016/j.vetmic.2005.11.068[Crossref], [PubMed], [Web of Science ®][Google Scholar]) or quickly disappear possibly caused by the intensive comb building activities of the swarm bees (Ascosphaera apis, Aronstein & Murray, 2010 Aronstein, K.A., & Murray, K.D. (2010). Chalkbrood disease in honey bees. Journal of Invertebrate Pathology, 103, S20S29.10.1016/j.jip.2009.06.018[Crossref], [PubMed], [Web of Science ®][Google Scholar]). This escape is beneficial for the start and building of the own host (=swarm) parasite relationship, a little respite is welcome because there are already enough challenges for a swarm to survive. In the wild, not even a quarter of the prime swarms survive, even though they found a nest. This can be explained by their inability to build a strong enough population of bees and food supplies for the winter (Seeley, 1995 Seeley, T.D. (1995). The wisdom of the hive. London: Harvard University Press. [Google Scholar], 2017b Seeley, T.D. (2017b). Life-history traits of wild honey bee colonies living in forests around Ithaca, NY, USA. Apidologie. doi:10.1007/s13592-017-0519-1[Crossref][Google Scholar]).

Not only parasites, but the entire microbiome, the microorganisms living together with and within the bees and the colony, is inherited vertically when a colony swarms. The microbiome may play important roles in the metabolism of the colony as a whole (Özkirim, 2012 Özkirim, A. (2012). Seasonal microflora, especially winter and spring. In D. Sammataro & J.A. Yoder (Eds.), Honey bee colony health: Challenges and sustainable solutions (pp. 1320). Boca Raton, FL: CRC Press. [Google Scholar]).

Introduction of a New Queen: Vertical or Horizontal Transmission of Parasites?

It is a beekeeping practice to “rejuvenate” a colony by removing the old queen and introducing a young fertilized (or optionally a virgin) queen. Queens are sometimes bred by grafting larvae from a selected colony into artificial queen cells and, after emergence, getting them to mate with selected drones in a mating station. This rearing of queens from selected grafted larvae is not a common practice in the Netherlands where most beekeepers allow their colonies to rear their own queens, but in surrounding countries it often is (Büchler, Berg, & Le Conte, 2010 Büchler, R., Berg, S., & Le Conte, Y. (2010). Breeding for resistance to Varroa destructor in Europe. Apidologie, 41, 393408.10.1051/apido/2010011[Crossref], [Web of Science ®][Google Scholar]). What are the consequences of such reproduction/propagation for the transmission and relationship with parasites? While the new queen is introduced into an unrelated colony which might carry different parasites, she might also be bringing her own parasites (plus parasites she may have got from the drones) into this new colony. Thus, this process might raise both vertical and horizontal transmission of parasites. Likewise, the local parasites are suddenly exposed to new genotypes and therefore, at each introduction of a foreign queen, the host-parasite interactions are reset. This disturbance would be minimized by introducing queens originating from the same apiary.

Recently, a study by Salmela, Amdam, and Freitak (2015 Salmela, H., Amdam, G.V., & Freitak, D. (2015). Transfer of immunity from mother to offspring is mediated via egg-yolk protein vitellogenin. PLOS Pathogens, 11(7), e1005015. doi:10.1371/journal.ppat.1005015[Crossref], [PubMed], [Web of Science ®][Google Scholar]) showed that the queen could add specific immune primers to eggs. These primers target specific parasites with which the queen has been in contact. This immune mechanism works through the yolk protein vitellogenin and can be considered as an analogue to “vaccination” of the offspring. This inherited immunity obviously loses most of its benefits when a queen is displaced, as a native daughter queen would probably already be better adapted, through her mother’s primers and her exposure to the local disease variants, than to the disease variants of a mating station or those of a new colony.

Some Examples of Beekeepers Counteracting Honey Bee Colonies

Parasites can also drift when colonies are placed close to each other, which is horizontal transmission. A recent study by Seeley and Smith (2015 Seeley, T.D., & Smith, M.L. (2015). Crowding honey bee colonies in apiaries can increase their vulnerability to the deadly ectoparasite Varroa destructor. Apidologie, 46, 716727.10.1007/s13592-015-0361-2[Crossref], [Web of Science ®][Google Scholar]) compared the development and mite infestation of colonies placed either in an apiary oriented in a row, or freely dispersed (distance between the colonies ~ 20 to 50 m) in woods surrounding the apiary. The study showed that, regardless of the colony location, colonies that had swarmed had a lower mite infestation than colonies that had not swarmed. This might be explained by the broodless period following the departure of a swarm. In the colonies that had not produced a swarm, the mite infestation increased strongly, and some did not survive the following winter. Remarkably, during the summer, in the colonies that had swarmed (and had a lower infestation), the infestation increased again in the row apiary, but not in the colonies dispersed in the wood. Seeley & Smith explain this by drifting of bees at the row apiary: many workers and drones from the swarmed and non-swarmed colonies mixed together, while this did not occur in colonies placed in the woods. Additionally, mated queens returned more successfully to their original colony when it was placed in the woods. The research shows that beekeepers can greatly stimulate varroa infestation by: (1) preventing swarming (which leads to continuous breeding), (2) putting colonies close together in a row, and (3) keeping colonies already having a high infestation in the same apiary with low infestation colonies (so the infested colonies can collapse and be robbed by neighboring colonies, which will take over the mites). Although these results might not seem spectacularly surprising, the difference in the dynamics of colonies in a row versus scattered colonies is relevant.

Summary

The honey bee is in Europe an endemic and wild species, with regional subspecies and many local adaptations. Although subspecies and populations have been hybridized, and despite some selective breeding, the honey bee still behaves naturally and increases its fitness through continuous local adaptation. In order to evolve more resilience against the varroa mite, a major threat, two ways are open: (1) targeted selection and breeding on a large or regional scale, and (2) natural selection for fitness in the presence of the varroa mite. While the success score for selective breeding is still scant, natural selection has delivered a few described cases of resistance, all in relatively short time periods.

Resilience of an organism towards parasites and diseases can be obtained by resistance (the disease/parasite is hampered in its development and fitness) and by tolerance (the damage caused by the disease or parasite is avoided or restraint). Resistance and tolerance can act concurrently. A balanced relationship between host and parasite can develop through resistance and tolerance, and an important condition to reach such a balance is that the disease or parasite is vertically transmitted: from mother to offspring. When a parasite is transmitted horizontally, such a balanced relationship struggles to develop. With natural reproduction of honey bee colonies, parasites are transmitted vertically onto the new generation. Method (2) of natural selection does not interfere with this transmission route. By replication or rejuvenation of colonies with the introduction of foreign queens (method (1)), the transmission is largely horizontal. This applies as well for the transmission of beneficial organisms (symbionts) in the colony.

In addition to reproduction of colonies and selective breeding, many other methods applied by beekeepers conflict with the bee colonies’ behaviours and resilience traits against parasites and diseases. Aligning methods to the natural traits of the bees, as well as the decision to start selection, targeted or natural, should be done with prudence to avoid evitable collateral damage.

Suggested Reading and Acknowledgements

Since we started writing this plea, Willem Boot, Bram Cornelissen and Henk van der Scheer as well as two anonymous referees critically read and commented. Thanks for that. In the meantime, Peter Neumann and Tjeerd Blacquière wrote the “Darwin Cure” paper (Neumann & Blacquière, 2017 Neumann, P., & Blacquière, T. (2017). The Darwin cure for apiculture? Natural selection and managed honey bee health. Evolutionary Applications, 10, 226230.10.1111/eva.2017.10.issue-3[Crossref], [PubMed], [Web of Science ®][Google Scholar]), which discusses some of the topics covered in this article. Happily, a growing number of scholars recognize the importance of a Darwinian approach to beekeeping (Brosi et al., 2017 Brosi, B.J., Delaplane, K.S., Boots, M., & de Roode, J.C. (2017). Ecological and evolutionary approaches to managing honey bee disease. Nature Ecology & Evolution, 1, 12501262.10.1038/s41559-017-0246-z[Crossref], [PubMed], [Web of Science ®][Google Scholar], Seeley, 2017a Seeley, T.D. (2017a). Darwinian beekeeping: An evolutionary approach to apiculture. American Bee Journal, 2017, 277282. [Google Scholar]). Let us realize that it is the only way to protect and conserve our honey bees: let us as beekeepers carefully explore beekeeping methods that allow the bees to help themselves by using their own resilience capacities.

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