A researcher says he was surprised to find how four samples of New Zealand honey contained traces of a class of pesticides known for their role in the decline of bees.

Professor Edward Mitchell, presently based at Crown research institute Landcare Research, led a new international study that suggested three quarters of the honeys produced throughout the world contain neonicotinoids, or neonics, which have been shown to cause harm to a large number of non-target species.

Neonics account for one third of the global pesticide market and are used to protect crops from insect pests.

Because neonics are found throughout targeted plants, including the pollen and nectar, bees are contaminated when they forage, resulting in contaminated honey.

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They have been available for use in New Zealand for more than 20 years, but remain subject to strict regulations.

The Environmental Protection Agency (EPA) has set special rules to protect bees which prohibit any spraying near hives, on crops likely to be visited by bees or when bees are foraging, or when flowering crops, plants and weeds are present in the treated area.

The EU has already moved to restrict the use of three neonicotinoid insecticides - clothianidin, imidacloprid and thiamethoxam - in response to concerns about colony collapse disorder.

Colony collapse disorder has not been seen in New Zealand and the EPA has stated it's confident that the rules placed on neonicotinoids here adequately protect our pollinators.

Conducted in 2015 and 2016, the study analysed 198 honey samples from around the world, looking for the five most commonly used neonics: acetamiprid, clothianidin, imidacloprid, thiacloprid and thiamethoxam.

The research was carried out with analytical tools to detect trace concentrations of neonics in complex matrices, such as honey, at the University of Neuchatel in Switzerland, where Mitchell also heads a soil biodiversity lab.

Seventy-five per cent of the honey samples contained at least one of the five tested substances, with the highest levels found in North America.

Thirty per cent of all samples contained a single neonic, 45 per cent contained between two and five, and 10 per cent contained four or five.

The measured concentrations of neonics were below the maximum authorised levels for human consumption, and Mitchell said the large majority of studied samples did not represent any health risk for consumers.

Mitchell said some traces of neonics were present in all four samples collected from New Zealand.

"I think that even Kiwis will be surprised to know that three of the four samples were Manuka honey and all were contaminated," he said.

"The explanation of course is likely that most Manuka honey is mixed with clover or other 'cheaper' honey which is likely where the pesticides come from."

Mitchell believed their use should be reassessed here and overseas.

"I firmly believe that the conventional agriculture that massively uses pesticides is not a long-term solution and that better, cleverer options exist and can be developed," he said.

"For bees and other pollinators neonicotinoids are clearly identified as a major problem. France is now banning these pesticides. I think New Zealand should also consider this."

The study follows two other major papers published this year which focused on neonicotinoids.

One, published in Science, compared the effects of neonicotinoid-treated crops on three bee species across Hungary, Germany and the United Kingdom and found different results.

Insecticide residue in bees nests was linked to lowered reproductive success in all three countries, but survival over winter was only affected in the UK and Hungary.

The second study, in Canada, showed more convincing evidence about effects on bees.

In response to the papers, Plant and Food Research pollination scientist Dr David Pattemore noted in Sciblogs.co.nz how there was no net effect of neonicotinoids on honey bees in New Zealand, as numbers of hives continue to rise, but there were localised effects of pesticides on hives, usually due to non-neonicotinoid pesticides rather than neonicotinoids.

"The colony deaths experienced with these more traditional pesticides are much more severe than the sub-lethal effects of neonicotinoids on overall colony reproductive fitness," Pattemore wrote.

Of the two papers, he concluded: "It could be that this is the start of a wave of studies that start to build a consensus that these pesticides also pose an undue risk to honey bee populations, or it could be that further studies reveal this specific threat to be minor compared to other pressing issues like organophosphate pesticides, loss of forage resources, climate change, and pests and pathogens.

"Sometimes in science you just need to sit and wait as the studies accumulate."