Neonicotinoid pesticides and bees

Dr Ben Woodcock, from the Centre for Ecology and Hydrology (CEH),was the second speaker on ‘Neonicotinoid pesticides and bees at our annual Cornwall Beekeepers Association/West Cornwall Beekeepers Association ‘Bit of a Do’ conference this September.

Ben is an Ecological Entomologist in the Community Ecology Group at CEH. He began his talk with a bit of background on how bees are doing in the UK, and why neonics may have contributed to the decline of some species. At the moment honey bees can only deliver about 34% of pollination demand in the UK, so farmers do need wild solitary and bumble bees for pollination too. There are a few species which have done really well under modern agriculture – for example, the Ashy mining bee. But there are plenty of others doing really badly.

The issue with neonicotinoid pesticides (neonics) is that they stay inside the pollen and nectar of treated plants over a long period of time (but at a low concentration). Typically test studies into the toxicity of neonics are just short-term studies carried out over about ten days, whereas in real life neonics affect honey bee colonies over periods of months.

Ben mainly discussed two studies he’s worked on which investigated the effect of neonics on bees. The first was:

Impacts of neonicotinoid use on long-term population changes in wild bees in England (Nature Communications, 2016; 7: 12459.)

Ben and his fellow researchers divided 62 species of wild bees into two groups:

  • 34 known to forage on oilseed rape (OSR)
  • 28 not known to forage on OSR.

The study found that wild bee species which forage on OSR were 3x more negatively affected by neonics than non-foragers. Ben stressed that neonics are just one factor affecting bees. However, the research indicates that they add detrimental extra pressure on wild bee species.

Bumble on blackberry bramble

The second study Ben mentioned was one he worked on, a big pan-European study across three countries, the UK, Hungary and Germany:

Country-specific effects of neonicotinoid pesticides on honey bees and wild bees (Science 30 Jun 2017: Vol. 356, Issue 6345, pp. 1393-1395)

He acknowledged that the funding for this was controversial, as the pesticide giants Bayer and Syngenta contributed £3m towards it. To ensure that the research remained impartial, the results were peer-reviewed and all emails associated with the research were recorded.

In the study 36 farms across the three countries were each allocated to a treatment: no neonics (control), Modesto (Clothianidin) or Cruiser (Thiamethoxam) – Modesto and Cruiser are big neonic products. There was an average of 60 hectares of sown OSR surrounding the farms. Six honey bee hives, twelve buff-tailed bumble colonies and a number of red-mason bee nests were put at each site. The study looked at the resulting overwintering success, colony strength and forager mortality of the bees.

With the honey bee hives, the honey bees exposed to Clothianidin in Hungary and the UK suffered higher mortality over the following winter. The neonics appeared to have less of an effect on the German honey bees. Ben said this may be because the bees relied more on OSR in the UK and Hungary, plus the OSR happened to flower later at the German sites, so the German bees had a more varied diet. At the beginning of the study the German honey bee bee hives were also less diseased, with lower varroa levels. Whereas the UK hives sourced for the study happened to be quite small and diseased – hives in a poor environment with a lower variety of forage crops are more vulnerable to disease to begin with.

For the wild mason and bumble bees, the higher the concentration of neonics found in their nests, the more their reproductive potential (measured in new queen or egg cell numbers) declined.

Ben then went on to talk about neonic residues in honey, which he studied in Woodcock et al (2018)  ‘Neonicotinoid residues in UK honey despite European Union moratorium‘. Neonic residues were identified in the honey samples, even for honey harvested after the moratorium in 2014. However, the concentrations were typically low and the likelihood of honey containing neonicotinoid residues was higher before the moratorium than after it. There’s a National Honey Monitoring Scheme run by CEH which UK beekeepers can get involved with – donate honey and they do analysis on it to identify the mix of pollens collected by the bees. The samples are also being archived for research in the future. If you’re into Twitter you can follow the scheme at @CEH Honey.

Following the neonics ban, farmers haven’t all switched to organic methods and stopped treating their oil seed rape. Instead, they’re using pyrethroid insecticides more – but some of the main species of aphids and beetles that feed on OSR have developed pyrethroid resistance. As a result, Ben suggested that OSR may stop being an economically viable crop in some parts of the UK. Unfortunately there is no obvious big alternative crop which is bee friendly. Soya is likely to expand in the UK, but it doesn’t require insect pollination.

Emily Scott, CBKA member

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