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Bedrohungen für Bienen

Tote Biene

(deutscher Text kommt bald)

 

Given the numerous services honeybees offer us, it is unfortunate to see how poorly we so often treat them. We are indeed endangering their existence and the practice of beekeeping itself through some of our activities. In the USA for example, honey bee colonies are dying off at a much higher rate than usual, values between 30 and 45% losses per year being repeatedly reported on a national scale. This phenomenon is known as the Colony Collapse Disorder (CCD) and its causes are still uncertain, though most scientists agree that an array of threats likely play a role.

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First, there is of course the direct and chronic exposure to chemical spraying in fields, gardens, and public spaces (1,2). Those sprayings also contaminate the nectar and pollen collected by bees, being then ingested by them (3). For example, the now notorious neonicotinoid pesticides act as neurotoxins and a very small dose can potentially kill millions of bees (4,5). These poisons, present in nectar and pollen, are brought back to the hives, messing up with the nervous and orientation systems of all the bees in the colony. Severely affected bees have reduced learning, feeding, and homing abilities thus greatly endangering their survival even at sub-lethal doses (5,6). Moreover, neonicotinoids do not only harm bees but a very wide range of other animals, including other invertebrates like bumblebees and butterflies but also birds and potentially bats (2,7).

Chemical sprayings also have the important indirect negative effect of destroying valuable nectar sources (1,8). This leads to a second major threat to honeybees: the dramatic lack of forage and malnutrition they experience. This is mainly caused by two factors. First and as we just mentioned, there is the degradation of natural flower habitats through pesticide sprayings or other human activities. The second is the prevailing existence of large monocultures in today’s agriculture (9). As for us, bees need a diverse diet to live healthy (3,10): we would not be very healthy eating only white sugar and pure fat. Plus, a large monoculture is only an abundant source of food for a short period of time, while bees need a diverse diet all along their active season.

Large monoculture

Those large monocultures are thus not sufficient for bees to live all year round, which brings most beekeepers providing crops pollination services to impose a migratory lifestyle on their hives. This results in several problems such as temperature fluctuations and bad sanitary conditions, reducing honey bees’ resilience to other difficult conditions and commonly leading to 10% colony mortality after transportation (1). Another issue with this migratory lifestyle is an increased exposure to pathogens and parasites which spread more easily in meeting points where thousands of hives come together each year to be redistributed. Unfortunately, parasites such as the varroa mite are likely to play a major role in the CCD phenomenon (10,11), though the chemical treatments commonly used against them have also been shown to exacerbate colony mortality (10,12).

 

Another hive management-related threat is the fact that to maximize profits, many beekeepers will harvest all the honey they can, leaving none to the bees for the winter. Instead, they feed the bees with high fructose corn syrup (HFCS) or other substitutes. While the nutritional advantages of honey are believed to provide bees with increased defenses, HFCS could weaken their immune system and thus further decrease their ability to fight off diseases, parasites, and pesticide ingestion (13).

Eucalyptus plantation: a dead landscape for pollinators

The air pollution from our industries is another threat to bees. Indeed, bees and other pollinators follow the scent trails emitted by flowers to find them. However, air pollution, even at moderate levels, degrade those floral volatile trails which can greatly confuse pollinators and increase their foraging time where they search for their food, potentially affecting their resilience and general fitness (14,15).

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And then there are the more and more extreme climate events such as drought or heavy rain which affect nectar and pollen availability and further reduce food availability for the bees, or abnormal temperature fluctuations which impacts bees’ lifespan as well as the vegetation they depend upon (1,10).

As if these listed single threats were not enough (and the list is not exhaustive), they don’t always simply add up, they interact together (see e.g. ref. 3). Here we will only describe a few examples of this. First, there is a synergy between certain pesticides and fungicides leading to increased toxicity (3,4), which is also true between agricultural pesticides and varroacides (3). Certain combinations can even lead to up to a 1000-fold increased toxicity (16).

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Finally combinations of threats, especially between pesticides, malnutrition, and parasites, are strongly associated with increased bee mortality and CCD (3,4,11). For example, when combined, pesticide exposure and pathogens lead to an up to 2-fold increased bee mortality, affecting vital functions in the colony as well (17). Pettis et al. (18) further found that pollen with traces of pesticides or fungicides leads to an at least twice higher risk for bees to contract pathogens. It is therefore bad news that they also detected traces of 35 different pesticides in their pollen samples! Malnutrition also appears to reduce bees’ resistance to pesticide exposure and to pathogens (3).

Note that many statistics presented here came from studies conducted in the USA. Though often not as bad, the situation is similar in Europe and CCD is widespread (10). In Europe, agricultural policies are smarter and stricter and rates of colony mortality are lower though still worrying (1). Note also that not only honey bees but also wild bees and other insects are threatened by many of the same threats and that they too offer us highly valuable services (19-22). In Germany for example, it has been shown that over 75% of flying insects disappeared over the last 27 years, potentially impacting the functioning of many ecosystems (7).

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Of course, there are several other factors that can affect bees’ mortality and much more investigation are needed to get a more complete assessment of the situation (10). However, with the knowledge we already have, there are several solutions at our disposal to help us create healthier habitats for us and for insects in general. These solutions are safe, can only help us, and mainly require the willingness to change some of our ways…this is where permaculture can play an important role.

     References

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  1. Kluser et al. 2010. UNEP 2010 - UNEP Emerging Issues: Global Honey Bee Colony Disorder and Other Threats to Insect Pollinators.

  2. Task Force on Systemic Pesticides. 2015. Worldwide integrated assessment of the impacts of systemic pesticides on biodiversity and ecosystems, 175 pp.

  3. Thompson. 2012. Interaction between pesticides and other factors in effects on bees. Supporting Publications, 2012:EN-340, European Food Safety Authority, 204 pp.

  4. Hopwood. 2012. Are neonicotinoids killing bees? A review of research into the effects of neonicotinoids insecticides on bees, with recommendations for action. The Xerces Society for Invertebrate Conservation, 44 pp.

  5. Goulson. 2013. Neonicotinoids and bees: What's all the buzz? Signigicance, June: 5-9.

  6. Henry et al. 2012. A common pesticide decreases foraging success and survival in honey bees. Sciencexpress, doi: 10.1126/science.1215039.

  7. Hallmann et al. 2017. More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PlosONE, doi: 10.1371/journal.pone.0185809.

  8. Benbrook. 2009. The Organic Center: Critical issue report, 69 pp.

  9. Spivak et al. 2011. The plight of the bees. Environmental Science & Technology 45: 34-38.

  10. Haubruge et al. 2006.. Notes fauniques de Gembloux 59: 3-21.

  11. Le Conte et al. 2010. Apidologie 41: 353-363.

  12. Hawthorne and Dively. 2011. Killing them with kindness? In-hive medications may inhibit xenobiotic efflux transporters and endanger honey bees. PLoS ONE, 6, e26796.

  13. Mao et al. 2013. Honey constituents up-regulate detoxification and immunity genes in the western honey bee . PNAS 110: 8842-8846.

  14. McFrederick et al. 2008. Air pollution modifies floral scent trails. Atmospehric Environment 42: 2336-2348.

  15. Fuentes et al. 2016. Air pollutants degrade oral scents and increase insect foraging times. Atmospheric Environment 141: 361-374.

  16. Iwasa et al. 2004. Mechanism for the differential toxicity of neonicotinoid insecticides in the honey bee, . Crop Protection 23: 371-378.

  17. Alaux et al. 2010. Interactions between microspores and a neonicotinoid weaken honeybees (). Environmental Microbiology 12: 774-782.

  18. Pettis et al. 2013. Crop pollination exposes honey bees to pesticides which alters their susceptibility to the gut pathogen . PLoS ONE, 8: e70182.

  19. Steffan-Dewenter et al. 2005. Pollinator diversity and crop pollination services are at risk. Trends in Ecology and Evolution 20: 651-652.

  20. Losey and Vaughan. 2006.. BioScience 56: 311-323.

  21. Garibaldi et al. 2013. Wild pollinators enhance fruit set of crops regardless of honey bee abundance. Sciencexpress, doi: 10.1126/science.1230200.

  22. Rader et al. 2016. Non-bee insects are important contributors to global crop pollination. PNAS 113:146-151.

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