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Scientists publishing in Science examine the exposure of honeybees to neonicotinoids.
Dr Chris Connolly, Reader in Neurobiology at the University of Dundee, and who wrote a Perspectives article published alongside the research, said:
“This is a very interesting and timely study into how widespread is the exposure of honeybees to neonicotinoids. The findings are alarming, neonicotinoids have become so globally ubiquitous that they are now present in 75% of all honey. The levels of these chemicals detected in honey are unlikely to be a hazard to human health as they are present at very low levels and below the limit authorised for human consumption. At these low levels, they are also not likely to be lethal to bees. However, the levels detected are sufficient to affect bee brain function and may hinder their ability to forage on, and pollinate, our crops and our native plants.
“Clearly, the use of neonicotinoids need to be controlled. Their widespread use on crops is due to their prophylactic use, as insurance against the possibility of future pest attack. The neonicotinoids are highly effective insecticides with low toxicity to humans, but this unnecessary overuse is also driving the development of pest resistance against them. It is time that these chemicals are heavily restricted for use. In this way, their impact on the environment can be limited and their efficacy against pests preserved for when there is no other alternative option.
“An interesting point raised in this study is that honey could be used as a tool to sample environmental contamination. Therefore, this approach could address the effectiveness of the current EU moratorium where the use of some neonicotinoids on bee-visited crops is banned. Is honey within the EU now free of these neonicotinoids? Or does its continued use on other crops reach bee-visited plants and still accumulate in their honey?”
Dr Paul Neve, Weed Ecologist and Lead of Smart Crop Protection (SCP, one of the institute’s five strategic programmes), Rothamsted Research
“It is unsurprising that levels of neonicotinoid insecticides are detectable in honey. It is likely that other (untested) pesticides might also be present. The major important questions revolve around potential impacts which are not addressed in the paper with any new science. All levels are below mandatory exposure levels for human consumption. Questions relating to chronic bee exposure remain unanswered, as noted by the authors. These questions can only really be addressed with large scale epidemiological studies, which are incredibly hard to perform.
“We need to remain open-minded and base decision-making relating to pesticide regulation on a strong science base, acknowledging that pesticides can have unacceptable negative impacts, but not forgetting their large role in securing productive harvests. The Rothamsted Smart Crop Protection programme is working to develop more targeted approaches for pest control that can reduce pesticide use and make application more precise. This programme is also working to develop alternatives to pesticides. The insect molecular biology group at Rothamsted Research is working to understand the basis of insecticide selectivity, to help efforts to design pesticides that have fewer non-target impacts.”
Dr Jonathan Storkey, Plant Ecologist and Lead of Achieving Sustainable Agricultural Systems (ASSIST, one of the institutes five strategic programmes), Rothamsted Research, said:
“There is no suggestion in the paper of a risk to human health, however, the levels recorded (up to 56 ng/g) lie within the bioactive range that has been shown to affect bee behaviour and colony health – scientists showed earlier this year that levels of less than 9 ng/g reduced wild bee reproductive success.1
“I therefore agree with the authors that the accumulation of pesticides in the environment and the concentrations found in hives is a serious environmental concern and is likely contributing to pollinator declines.
“However, this situation has arisen as much through the over-reliance and imprudent use of neonicotinoids as through the inherent properties of the chemistry; which can be argued are more benign than the alternatives (multiple sprays of synthetic pyrethroids) that are now being used in their stead where neonicotinoids have been banned.
“Rather than seeking an outright ban, research should focus on developing strategies for limiting the use of neonicotinoids across crop rotations, using all the principles of Integrated Crop Management2 as well as integrating additional foraging resource into the landscape for pollinators to reduce the exposure of hives.”
1 Woodcock B A, Bullock J M, Shore R F, Heard M S, Pereira M G, Redhead J, Ridding L, Dean H, Sleep D, Henrys P, Peyton J, Hulmes S, Hulmes L, Sarospataki M, Saure C, Edwards M, Genersch E, Knabe S, Pywell R F. 2017. Country-specific effects of neonicotinoid pesticides on honey bees and wild bees. Science 356:1393-+.
2 Barzman M, Barberi P, Birch A N E, Boonekamp P, Dachbrodt-Saaydeh S, Graf B, Hommel B, Jensen J E, Kiss J, Kudsk P, Lamichhane J R, Messean A, Moonen A C, Ratnadass A, Ricci P, Sarah J L, Sattin M. 2015. Eight principles of integrated pest management. Agronomy for Sustainable Development 35:1199-1215.
Dr Lynn Dicks, Natural Environment Research Council Fellow, School of Biological Sciences, University of East Anglia, said:
“This is the first time we’ve seen a global picture of bee exposure to neonicotinoid insecticides, and it is sobering. If honey bees are exposed to these chemicals, so are all the wild pollinators that also feed on nectar and pollen from crop flowers and flowers growing around crops. That includes many of the 20,000 species of wild bee in the world. We know from data in North West Europe and North America that many wild bees and butterflies have declined, but there aren’t enough long-term data to know what’s happening to these insects in the rest of the world. However, the threats that are interacting to cause pollinators to decline, which include agricultural intensification, habitat loss, agricultural chemicals and climate change, are happening in many parts of the world, as this study demonstrates for agri-chemicals.
“Having said that, the severity of the global threat to all wild pollinators from neonicotinoids is not completely clear from this study, because we don’t know how the levels measured in honey relate to actual levels in nectar and pollen that wild pollinators are exposed to. Honey is made from nectar collected over periods of time, concentrated into a thick syrup. A relatively small proportion of the honey samples had total neonicotinoid concentrations higher than 10 parts per billion (ppb), where there is clear evidence of impacts on honey bee behaviour, although bee immune systems are affected at levels between 1 and 10 ppb. We can infer from this study that social bee species that make honey (including wild honey bees, but also many species of stingless bee) are consuming these levels at some times of year.”
Prof. Dave Goulson, Professor of Biology at the University of Sussex, said:
“It is not at all surprising to hear that the large majority of honey samples from around the world are contaminated with neonicotinoid insecticides. Global use of these chemicals continues to increase, despite repeated warnings from scientists that they are impacting on bees, butterflies, aquatic insects and more. Neonicotinoids are highly persistent in the environment, and frequently turn up in soils, water samples, and in wildflowers, so we would expect to find them in honey. Entire landscapes all over the world are now permeated with highly potent neurotoxins, undoubtedly contributing to the global collapse of biodiversity. Some of us have been pointing this out for years, but few governments have listened. It is hard not to feel a sense of deja vu: Rachel Carson was saying the same things more than 50 years ago, but we seem not to have learned any lessons. It is high time that we developed a global regulatory system for pesticides, to prevent such catastrophes being repeated over and over again.
“The fact that neonicotinoid contamination in Europe was barely lower than in North America suggests that the EU moratorium has not been successful in reducing exposure of bees.
“Although bees have grabbed the limelight with regard to impacts of neonicotinoids, there is every reason to believe that they will be impacting all beneficial insects that live in or near farmland.
“The implications of this new study for human health are unclear. It demonstrates beyond doubt that anyone regularly eating honey is likely to be getting a small dose of mixed neurotoxins. In terms of acute (short-term) toxicity, this certainly won’t kill them and is unlikely to do measureable harm. What we don’t know is whether there are long-term, chronic effects from lifetime exposure to a cocktail of these and other pesticides in our honey and most other foods. For obvious reasons, it is impossible to do a proper experiment to test this.”
Prof. Nick Birch, senior scientist at the Hutton Institute’s Ecological Sciences group, said:
“Neonicotinoids (NNIs) are widely used in agriculture, often as seed coatings (prophylactically at planting) or sometimes as sprays (reactionary to pest pressure during the growing season). To me it is not surprising that low levels of one or more pesticides are present in some honey samples, given their global use and the sensitivity of pesticide detection methods now available.
“Without seeing the detailed Methods and Results tables it is not clear what controls were run and what was the variability (noise) associated with NNI measurements, but I assume referees saw this information and it was validated by analytical experts.
“What seems unfortunate, given we know that bees react to ‘cocktails’ (mixtures) of pesticides via landscape scale foraging, is the lack of information on other types of pesticides possibly present in these samples. For example, scientists recently demonstrated that a commonly encountered fungicide doubles the toxicity of certain NNIs when they are encountered together.1 This implies, as other studies have shown, that multiple stressors (eg ‘pesticide cocktails’) could have an effect on bees if exposure is sufficient over time and space.
“Interpretation of these results in terms of ‘regional risks to bees’ remains a complex issue; bee species and populations differ in their exposure to NNIs and in their sensitivities to pesticide mixtures. Bee keepers often move honeybee hives around different crops and regions, so correlating regional honey NNI content directly to observed bee effects in a locality could be difficult.
“As a more general indicator of ‘average bee exposure’ to NNIs, honey content in a region could be useful as part of an environmental monitoring programme at landscape scale (termed ‘pesticidovgilance’)2. However, as other studies have recently noted3 pesticide exposure varies by country and does not fully explain any negative NNI effects on bees. Other factors such as non-contaminated food sources in the region and regional bee disease pressure play a part and can mitigate the negative impact of NNIs (e.g. in Germany).
“My overall perspective is that the paper is useful but only part of a bigger and more complex agroecological picture involving variability in bee sensitivities, variability exposures, interactions with other stressors and with regional crop and habitat management practices.
“Future risk management strategies for bees and other pollinators should be able to reduce impacts of NNIs via suitable monitoring mitigation measures; for example, offsetting any negative impacts of pesticides by prudent management of pesticide use (‘Integrated Pest Management’) and by providing a disease-free and food-rich habitat for bees and other pollinators (‘Integrated Pest and Pollinator Management’).”
1 Tsvetkov et al, Science 356, 135-1395; 30 June 2017
2 (as explained recently by Milner and Boyd (2017) in Science 357 (6357)
3 (e.g. Woodcock et al, 2017 in Science 356, 1393-1395)
Prof. Felix Wäckers, Lancaster Environment Centre, Lancaster University, said:
“The study reports results from a global survey into neonicotinoid contamination of honey samples. The survey reveals the widespread contamination of honey with neonicotinoids, with 75% of honey samples testing positive for this group of broad acting insecticides at levels that are harmful to bees.
“This shows that honeybees are commonly exposed to this group of pesticides while collecting neonicotinoid-contaminated nectar from treated crops or from flowers that have come into contact with spray drift or soil residues. This level of exposure also applies to the wide range of other insects that depend on floral nectar, including wild bees, butterflies, and the numerous insects that provide natural pest control services.
“The actual level of exposure can be substantially higher, as the honey samples analyzed in this study represents an average of nectar collection over time and space. Peak contamination levels as experienced by insects collecting from treated crops will be (substantially) underestimated by the method used.
“This study provides further evidence linking neonicotinoid exposure to the dramatic global decline of (wild) bees, butterflies and insects in general.”
* ‘A worldwide survey of neonicotinoids in honey’ by E. A. D. Mitchell et al. published in Science on Thursday 5 October.
Declared interests
Prof. Chris Connolly: Commentary
Prof. Nick Birch:
Dr Lynn Dicks: I work informally as an advisor to Waitrose, Mars, Body Shop, Tesco, towards their objectives of biodiversity conservation, pollinator protection and sustainable supply chains. I have received a small amount of funding from Waitrose over the last five years, but don’t have any current funding from them.
None others received.