A bee feeding on a purple flower

Neonicotinoid replacement hinders bumblebee reproduction – Expert Reaction

A new family of pesticides, sulfoximines, which are expected to be a key replacement for neonicotinoids, may have sub-lethal effects on bumblebee colonies, according to a UK study.

Sulfoximine-based pesticides have been shown to be effective in targeting neonicotinoid-resistant species and have been approved for use in China, Canada and Australia, with licence applications progressing in several EU member states. However, the two classes of pesticide share a common biological mode of action and the sub-lethal effects of sulfoximines on pollinators have not yet been fully investigated.

The study found that bumblebee colonies exposed to the sulfoximine pesticide sulfoxaflor in a laboratory setting produced significantly fewer workers and reproductive male bumblebees once released into a field setting.

The authors suggest that sulfoxaflor exposure could lead to similar environmental impacts on pollinators as neonicotinoids in the absence of evidence-based legislation. They call for regulatory bodies to assess both the lethal and non-lethal consequences of novel insecticides before licencing them for use.

The UK SMC asked experts to comment on the study.

Dr Lynn Dicks, Natural Environment Research Council Fellow, University of East Anglia, said:

“This study is hugely important. It is well-designed and carefully done, using healthy wild bumblebees, and it shows an unacceptable scale of impact on bumblebee reproductive success, after realistic levels of exposure to sulfoxaflor (5 parts per billion for just two weeks). What a shame this kind of study isn’t a mandatory requirement for the manufacturing companies to conduct (and transparently report) prior to bringing products to market.”

Conflict of interst statement: “I am fully funded by the Natural Environment Research Council. Current students in my research team are co-funded by Hutchinsons Ltd, BerryWorld Group, the Bumblebee Conservation Trust and Highways England. I work directly with Primafruit and Labrunier group, but we have no funds directly from them. I work, and have co-authored papers with, a range of policy and business organisations, including Defra, Natural England, Syngenta and Bayer, but I have never received any direct funding from Syngenta or Bayer. I have acted as a consultant to the Cambridge Institute for Sustainable Leadership, on projects funded by Mars and the Body Shop. I am a member of the Innovation Hub Science Committee for the Cool Farm Alliance, and my research group in the past has received funds from the Waitrose Agronomy Group.”

Prof Nigel Raine, Rebanks Family Chair in Pollinator Conservation at the University of Guelph, Canada said:

“This study provides an important first step towards understanding potential sublethal impacts for bees of exposure to sulfoximine insecticides at field-realistic levels. The findings of this study suggest that concerns over the risks of exposing bees to insecticides should not be limited to neonicotinoids.

“This study suggests that exposure to sulfoximine-insecticides, like neonicotinoids, can have substantial impacts on both the rate at which bumblebee colonies grow, and their ability to reproduce effectively. Such pesticide impacts on wild bees could have serious ramifications for the pollination of many crops and wild plants.

“Restrictions of neonicotinoid use, in response to concerns around pollinator health, make widespread use of alternative pesticides (including sulfoximines) much more likely. It is critical that we make informed decisions about which pesticides to use, and also if and when to use them, through understanding the likely risks of exposure to these chemicals for pollinators and other beneficial insects, and the critical ecosystem services they provide.

“Sulfoxaflor is a chemical in the sulfoximine class of systemic insecticides that kills insect pests by disrupting their nervous system. Sulfoximines bind to the same type of neurotransmitter (nicotinic acetylcholine) receptor in both pest- and beneficial insects, which are also affected by exposure to neonicotinoid insecticides.

“Farmers rely on pollinators and controlling pests to produce the food we eat. Choosing which pesticides are safest is a balancing act between the unintended consequences of their use for non-target organisms (including pollinators) and giving farmers the tools they need to control crop pests. Results from this study suggest we need more information about the impacts on beneficial insects, like pollinators, from exposure to pesticides being considered as neonicotinoid replacements.”

Conflict of interest statement: I am a former colleague of two authors of this study (Prof. Mark Brown and Dr. Elli Leadbeater) during the period we all worked at Royal Holloway University of London, and have co-authored works with both of them. I moved from the UK to Canada in May 2014, and I have no on-going research collaborations with any authors of this study.

“I am the author of the News & Views piece associated with the Siviter et al. study (Raine, N. E. 2018. A systemic problem with pesticides. Nature: doi:10.1038/d41586-41018-05917-41580).”

Dr Richard Gill, Senior Lecturer in Insect Ecology, Imperial College London, said:

“Sulfoximine-based pesticides are perhaps the new kids on the block, and one of the potential successors to the currently scrutinised neonicotinoids. By understanding the effects of sulfoxaflor on proxies of colony fitness of a key non-Apis insect pollinator, this report represents a novel study. Importantly, it takes advantage of previously tried-&-tested controlled neonicotinoid exposure experiments, field experiment designs and used locally adapted colonies by using wild-caught queens, all of which mean that the results of this study are likely to be reliable.

“There is currently limited data telling us what the field realistic concentration(s) of sulfoxaflor in the environment is, and more importantly what dosages foraging bees are exposed to. However, using data from a USA EPA cotton study, I feel the authors do an impressive and appropriate job of attempting to expose bees at the lower end of the range, representing a more worst-case scenario.

“I believe that the authors make two strong conclusions. Firstly, that male production is reduced in exposed colonies. Indeed, this is an important finding as one key aspect of social bee colony fitness relies on the number of sexual offspring that are produced. Interesting future work would be to see if measures of individual quality are lower in the males produced by sulfoxaflor exposure. Secondly, whilst colonies were only exposed during the first two weeks, effects on colonies were seen a number of weeks later. Provides an important insight as to how stress placed on a colony at the early stage can have effects later in the colony life cycle.

“The amount of work gone into rearing this many colonies and undertaking repeated census measures is impressive. However, two questions still require further enquiry: are there subtle but important effects on foraging behaviour that require more in-depth observational protocols?  How does variation in the timing of sulfoxaflor exposure affect colonies, whether it be variation in when colonies are placed in the field and/or when during the colony life cycle?

“This research again highlights that there may be susceptible developmental phases of bee colony lifecycles, with stress imposed at these points having the potential to lead to an eventual colony collapse. However, empirical studies looking into how variation in the timing of pesticide exposure affects colony functioning and fitness are currently limited.

“This study contributes further to our understanding of the hazard of pesticide exposure and the importance of using controlled exposure experiments. But there are still large evidence gaps as to our understanding of the risk of exposure and how frequently bees come into contact with pesticide residues in the environment.

“One of the significant contributions provided by this study is it showing that despite sulfoxaflor being a potential substitute for the criticised neonicotinoid predecessors, exposure to either of these chemicals can cause similar effects.

“The recently announced EU-wide ban in using specific neonicotinoids outside of greenhouses means that alternative pest control methods are required. The current preferred option is to find replacement synthetic chemicals. But if we have a very limited understanding of how pesticide replacements affect beneficial organisms, then do we have to laboriously repeat previous lab and field experimental setups using the new chemicals or agents? Whilst controversial and further research is required, it is sensible to ask the question: should we take advantage of what we know to date about neonicotinoids so that we can potentially use them more effectively and responsibly, rather than an outright ban if the non-target effects of replacements are unknown?

“It is becoming increasingly apparent that pesticide risk assessments require testing over chronic time, and that this needs to be representative of the period that high levels of pesticide residues are present in the environment during a season. Encouragingly, regulators have been considering and acting on this, but there appears still to be room for improvement.

“Furthermore, if we want to protect social bees, such as bumblebees and honeybees, then instead of exposure assays focusing on the health of individuals in isolation they must also understand how induced impairment translates to colony level effects. This study reaffirms this view.”

No conflict of interest declared.