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Honey bees are just one of the 20,000 known species of bees. Although small in number, they have an enormous role in supporting global food production. Worryingly, the numbers of these critical pollinators are dropping.
Honey bees have a delicate relationship with their environment; how the population copes with natural- and agricultural-induced stresses, and how much these stresses contribute to their decline is not fully understood. Research does, however, suggest that pesticide exposure, pathogens, and loss of habitat are prime factors in the bee’s decline.
Pesticides are highly toxic and crops are increasingly being treated with a wide variety with greater frequency, seriously harming nature and the environment. The effects of pesticides on the honey bee are widely documented, but what is less well known are the effects of sublethal pesticide exposure, i.e., the physiological and behavioral effects.
The Pesticide Problem
Honey bees are inadvertently exposed to pesticides as a result of spraying or seed coating. Aerial and vehicle-based sprayers widely distribute pesticides, but frequently reach areas they had not intended to such as bee foraging sites.
Seed coating is a more controlled way of dissemination, but because the pesticide is systemic it is taken up by every part of the growing crop, where it remains active. This means bees are ingesting the pesticide via the plant’s nectar and pollen. While this is not enough to kill the bee, it is enough to affect their ability to survive.
Bees subjected to sublethal pesticide exposure experience impairment in motor function, behavior and cognition, short- and long-term memory, and visual and associative learning. This decline in overall physiological functioning results in suboptimal performance by survivors, as well as an overall population decline.
Pesticides also suppress the bees’ immune system; exposed bees show increased loads of bacterial, fungal, and viral pathogens, and scientists are concerned this is increasing mortality. Bees also have fewer detoxifying genes than other insects, thus increasing their vulnerability. This reduced immunity could be a result of bees’ highly social behavior and adoption of a social detoxification system and herd immunity.
Pesticides also affect bees’ reproduction; there is reduced mating, and the queens produce fewer viable eggs. Bee development is also affected, both at the larval and juvenile stage, so fewer bees reach adulthood.
Mitigating the Effects of Pesticides
Pesticides clearly have a detrimental, if unintended, effect on the honey bee population. There is legislation coming into force across the EU and increasing public pressure to find alternatives to pesticides. But it is not as easy as simply banning their use.
Simply replacing one pesticide for another is not effective – the cycle of pesticide use needs to be broken for a better farming system. Farmers could introduce better farming practices, such as those seen in Italy in 2008, when seed coating was banned because of the honey bee decline. Instead of pesticides, farmers introduced crop rotation and saw no reduction in harvests.
These practices could be made mandatory, but this would not stop the beekeepers themselves from using fungicides and acaricides to protect their hives. Another option is to use a probiotic supplement that could be used alongside current apicultural and agricultural management practices to mitigate the side effects of sublethal pesticide exposure to improve the long-term survival of bees.
Pesticides found in honey around the world
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A recent study by Chmiel et al. to better understand the effects of pesticide exposure across the honey bee lifecycle explored the use of a lactic acid bacterial (LAB) supplement to mitigate the harmful effects of pesticides and pathogens. The LAB could be added to a simple sucrose syrup or pollen-substitute patties that act as sustenance for the bees.
LAB supplements containing Lactobacillus and Bifidobacterium species can reduce the absorption of the pesticide via degradation or sequestering ingested pesticides, which pass through the digestive tract rather than being absorbed. LAB supplements have been shown to reduce toxicity and have a protective effect on the host. However, more research is needed to investigate this potential in honey bees.
There are many potential LAB supplements; some have been shown to directly inhibit pathogens, enhancing the honey bees’ overall resistance to pathogens, while others produce biofilms or reduce viral loads in the bee.
We need to reduce our chemical reliance on pesticides; while they increase crop yields and help provide food security, they are harming the very insect needed to ensure this continuous supply of sustenance.
Simply banning pesticides is impractical, so a balance needs to be struck between their continued – but perhaps limited – use, and other alternatives. But what is clear it that saving the bees has never been more important.
References and Further Reading
Chmiel. J, et al. (2021) Understanding the Effects of Sublethal Pesticide Exposure on Honey Bees: A Role for Probiotics as Mediators of Environmental Stress – Frontiers in Ecology and Evolution: https://www.frontiersin.org/articles/10.3389/fevo.2020.00022/full. Accesses 10 May 2021.
The Problem with Pesticides – The Soil Association: https://www.soilassociation.org/causes-campaigns/reducing-pesticides/the-pesticide-problem. Accessed 10 May 2021.
Alternatives to Pesticides do exist – Pesticide Action Network UK: https://www.pan-uk.org/alternatives-to-pesticides/. Accessed 10 May 2021.
Save the Honey Bees – Pesticide Action Network Europe: https://www.savehoneybees.info/alternatives. Accessed 10 May 2021.