Field tests show insecticide impact on bees – Expert Reaction

Two large-scale field experiments have shown mixed effects of certain insecticides on honey bees and wild bees.

Neonicotinoids are insecticides broadly applied to many major crops but have been implicated in the decline of bees globally.

Two studies, published today in Science, found mixed results. Insecticide residue in bees nests was associated with lower reproductive success in Germany, Hungary and the UK, but survival over winter was unaffected in Germany.

The second study, in Canada, found that worker bees exposed to neonicotinoids had lower life expectancies and their colonies were more likely to lose queens.

The SMC gathered expert reaction to the two studies, please feel free to use these comments in your reporting. More information about the studies is available on

Dr David Pattemore, pollination & apiculture team leader, Plant & Food Research, comments:

“Two new studies published this week claim to show negative effects of neonicotinoids on honey bee colonies in real-world scenarios. One study does not really present clear evidence to support this conclusion, but the second does link neonicotinoid exposure to key longevity, hygiene and reproductive traits of honey bee colonies.

“One of the studies demonstrates synergistic effects between fungicides and neonicotinoids, which increase the mortality of bees exposed to the pesticides. One of the studies shows evidence of negative neonicotinoid effects on bumblebee and solitary bee reproductive output.

“Overall these provide a little more evidence about the effects of neonicotinoids, but there is still no scientific consensus emerging about the effect of neonicotinoids on honey bee health in realistic field situations.

“These two studies are unlikely to have implications for New Zealand in terms of regulations for the use of neonicotinoid pesticides. After reading these papers, my view is that we need to consider the synergistic effects of multiple agrochemicals on bee health and that it is timely to consider establishing long-term monitoring programmes for wild pollinator populations, including native and introduced bees, in New Zealand.”

Note: Dr Pattemore has also written a blog in response to the studies. Plant & Food Research occasionally has contracts to evaluate the efficacy or toxicity of pesticides, but Dr Pattemore hasn’t been personally involved in these trials to date.

Dr Jacqueline Rowarth, chief scientist, Environmental Protection Authority, comments:

“Research published this week indicates that prolonged exposure to neonicotinoid insecticides can negatively affect bees. The researchers also concluded that local environment and species influence impact of the chemicals. The research was done in the northern hemisphere near oilseed rape crops in Germany, Hungary and the UK, and in the commercial corn (maize)-growing area of Canada.

“For New Zealand, and the Environmental Protection Authority (EPA) which regulates the use of chemicals, focus on new research results includes applicability. Experts scan for new research constantly, and consider the results in the New Zealand context.

“New Zealand does not have the large tracts of land under cropping that are common in the northern hemisphere, and does have very strict regulations around timing of chemical application (e.g., not when the target for protection is flowering), delivery method, and seed treatment dust reduction. The northern hemisphere research comments on neonicotinoid dust being found in the pollen of flowering species surrounding crops ‘despite the use of dust-reducing lubricants’.

“In New Zealand the use of neonicotinoids in seed treatment has enabled very low rates of active ingredient, thereby reducing the number of insecticide treatments required to protect the crop. Residues of neonicotinoids have not been found in pollen or nectar of when the insecticide has been applied at label rates.

“The chemical of particular concern in the new research, clothianidin, is a seed treatment approved for cereals, maize/sweetcorn, grasses and forage brassicas. Only the brassica is a flowering crop, and it is eaten before it reaches maturity. The crops are not considered to be attractive to bees, unlike oilseed rape.

“The northern hemisphere researchers also comment on the increase in negative effects in bees when fungicides were used as well as the neonicotinoids and the confounding factor of climate change. This points to the complexity of identifying the problems with chemical exposure. Cold damp winters affect bee survival and there is an interaction with pests as well as food supplies (quantity and quality). These factors are difficult to disentangle. In New Zealand, feral bee numbers have been decimated by varroa mite, but managed bee hive numbers have increased. In Australia, which is varroa-free, no problems with bee survival have been reported. Neonicotinoids have been used for two decades.

‘Recognising on-going public concerns, the EPA is developing a pollinator strategy, working with the chemical industry and the apiculturalists, to ensure that decisions about chemical use are made on the basis of robust and appropriate research, whilst supporting pollinators and pollination.”

The EPA sets the rules for use of hazardous substances under the Hazardous Substances and New Organisms Act 1996 by assessing the environmental and economic risks and benefits to New Zealanders and the environment.

Associate Professor Peter Dearden, director, Genetics Otago, University of Otago, comments:

“The two Science papers (Tsvetkov et al and Woodcock et al) attempt to test the effect of common pesticides on bee colonies in situations that are as close to reality (in terms of exposure) as possible. This is a tricky thing to do, and something that has been criticised in previous studies of neonicotinoid exposure in the past. These papers do this well, and show that the effects of neonicotinoids are complex, but detrimental to bees.

“In Canada, Tsvetkov et al show clearly that neonicotinoid seed coatings have detrimental effects on bees, and that these effects are exacerbated by other agricultural chemicals. Woodcock et al show similar things in Europe, but add that the different cocktails of agricultural chemicals used in different countries have different effects, causing variation in the impact on bees in each location.

“This complexity of response to insecticides is not surprising, but these results clearly show that in general neonicotinoid exposure, even in sublethal doses, in field realistic tests, is detrimental to bees. This is a problem, but so is growing crops without pesticides.

“There is a balance to be had here if we are to produce food in large enough quantities to feed a burgeoning human population, without devastation of managed, and wild, pollinators. The hope of these papers is the variability seen in European countries, and the synergistic effects with other agri-chemicals seen in Canada. This suggests that we may be able to identify ways of using these chemicals, or combinations of these chemicals, to be less damaging to bees, and wild insects.

“The key message is, however, that in field realistic conditions, neonicotinoid seed treatments are bad for pollinators. Limiting their use in New Zealand, as well as researching how to develop pollinator friendly insecticides, or using insecticides in a less damaging way, is critical. The European studies show that agricultural practice varies the impact on bees. We need this research to be done in New Zealand to see how our practice is affecting our bees.”

Note: Dr Dearden has an MBIE grant to develop bee-friendly insecticides.

Professor Phil Lester, insect ecologist, Victoria University of Wellington, comments:

“Neonicotinoids are some of the most widely used pesticides in the world. They were developed in the hope that their use would be less harmful to non-target organisms, because by only coating crop seeds in this pesticide prior to planting the need for spraying entire environments can be reduced. Neonicotinoids are then expressed throughout the mature plant and affect only those organisms eating the plant. The issue is that neonicotinoids are expressed in the pollen and nectar too, which beneficial organisms like bees collect and eat.

“The European Union imposed a temporary moratorium on the use of the three key neonicotinoids in 2013 because of their potential to harm honey bees. In contrast, the government of New Zealand has joined with Australia in not imposing a ban or moratorium on the use of these chemicals. I think our governments have made exactly the right decision at this time.

“The work published by Tsvetkov and colleagues in Science today that indicates ‘Chronic exposure to neonicotinoids reduces honey-bee health near corn crops’. This study agrees with a large amount of previous work. If honey bees are exposed to and feed on high amounts of neonicotinoids the outcome is simply bad. Workers and queens will die. For those experiencing a sub-lethal dose, their foraging becomes less efficient. They undertake reduced hygienic behaviour in the hive and their immune system seems to be impaired. And their tolerance of other stressors bees experience in bee environments, in this case a fungicide, is reduced.

“The Tsvetkov study in cornfields of Canada clearly shows that field-realistic exposure to neonicotinoids can substantially reduce honey bee health.

“The second paper in Science today is from work within three different countries and examines three different bees. It also attempted to use field-realistic exposure to neonicotinoids. Populations of honey bees, bumble bees and a solitary bee were followed in the United Kingdom, Hungary and Germany.

“The team of authors led by Woodcock examined two neonicotinoid pesticides. They found a fascinatingly mixed bag of results. Both neonicotinoids resulted in significantly reduced numbers of honey bee eggs being produced in Hungary. But exposure to both pesticides in Germany resulted in significantly more eggs being produced. Neonicotinoids also seemed to result in higher numbers of workers surviving winter in Germany. In Hungary, fewer workers survived winter after exposure to one pesticide, but not the other chemical. Similarly, in the United Kingdom, there were negative and some positive effects of exposure to the different neonicotinoids.

“A take-home message the Woodcock publication is that the use different neonicotinoids can have different effects and these effects can be very country specific. After reading these results, if I was a grower in Germany I would be starting to question the European Union’s temporary moratorium.

“These studies highlight that for countries like New Zealand to effectively manage the use of neonicotinoid pesticides, we need data. We need to know what the effects of neonicotinoids are in our specific country and in the way we specifically use them. And we also need to know what the effects would be if we took them away. I’ve read reports that growers in the UK have had to now revert to broad spectrum pesticides that are considered worse for the environment and mean they cannot grow certain crops.

“In 2013, the Australian government undertook a review of “Neonicotinoids and the Health of Honey Bees in Australia”. They concluded that “the introduction of the neonicotinoids has led to an overall reduction in the risks to the agricultural environment from the application of insecticides”. They don’t currently think there is the scientific evidence to show that neonicotinoids are of widespread harm to bees in Australia. In fact, they stated that “The introduction of the neonicotinoid insecticides has brought a number of benefits, including that they are considerably less toxic to humans (and other mammals) than the organophosphorus and carbamate insecticides they have significantly replaced”.

“Honey bees in New Zealand have a plethora of known and scientifically demonstrated threats. Our honey bees have invasive, blood sucking mites. They have the Deformed wing virus which has been described as a key contributor to colony collapse around the globe. Our bees have bacterial pathogens like American Foulbrood that result in beekeepers burning their bees and hives. Fungal diseases are widespread. We also have management issues with the higher-than-ever numbers of managed hives, which are often managed poorly and over-stocked. These are real and known issues occurring for our honey bees now.

“I hope that the New Zealand government acts on studies like those from the Woodcock and Tsvetkov teams.

“But I’d personally be disappointed if that action was anything other than evidence- and science-based. Let’s gather the data. Then make the decision. It might be that like results from the Tsvetkov study, we find neonicotinoids are bad for our bees. Or we might be a Germany and find that they have few or even positive effects.”

Note: Professor Lester’s comments also appeared on The Conversation.