10 : Neonicotinoids
However, the author developed a technique to collect the nectar from the fl owers. It is a lengthy process to collect enough nectar, unfortunately, but the most accurate way to determine the levels of neonicotinoids in the nectar as encountered by foraging bees. The process involves sticking a small glass capillary down the fl owers at the nectaries to suck up the nectar via capillary action. See Figure 3 and Figure 4. Depending on the time of day and the fl ower, this yields approximately 1–10 µl of nectar per fl ower. Although this amount is not enough to fully analyse, it is possible to determine the amount of neonicotinoids per µl of nectar using this process. Studies in the author’s laboratory showed that for analysis (extraction and HPLC-MS) at least 50 µl is needed. This article is not the place to go into much detail of the results of the chemical analysis of all samples in the UK and worldwide. It is suffi ce to say that concentrations of the three commonly used neonicotinoids (imidacloprid, thiamethoxam and clothianidin) found in pollen and nectar are far below the acute toxic levels. Another important result to mention is that from all the samples analysed, only a percentage (often much less than 50%) of the samples actually contained any of the neonicotinoids. Where levels were found they ranged from 0.2 ng/g to 13.6 ng/g, with an average concentration of 6.1 ng/g in pollen and 1.9 ng/g in nectar. The only exception is with regards to guttation fl uid that often contains levels that are much higher and may reach the lethal dose. Dust from seed drilling machines can also increase the concentration locally.
A Real Threat?
Of all the various studies conducted to establish levels of neonicotinoids in the fi eld, it seems that the average concentration in pollen is 6.1 ng/g and in nectar 1.9 ng/g. However, it is important to emphasise again that several samples analysed showed no detectable levels of neonicotinoids. Assuming a foraging bee carries 25–40 mg of nectar or 10–30 mg of pollen and a colony typically stores 750 g of pollen in four days, the amount of a certain neonicotinoid that enters the beehive corresponds to anything between 8–11% of the acute oral dose. The neonicotinoid intake for nurse
www.bee-craft.com
Figure 3. Diagram showing the collection of nectar
bees via pollen or nectar then equates to 0.8–1.1% (via pollen) and 1.2–6.7% (via nectar) of the acute oral dose, respectively. The question still to be answered is how much of these neonicotinoids is accumulating over time in the beehive? Even though bees are not likely to be exposed to lethal doses, is there evidence of the effect on bees due to chronic exposure? Is there accumulation of neonicotinoids in the hive? Bees are known to clear imidacloprid from their bodies at 2 ng/day. Also, the fi gures used above to calculate the levels of these in the hive do not take into account that bees will feed on a variety of fl owers and that, of all the samples analysed, only a maximum of 50% contain neonicotinoid levels. What does this mean for accumulation in the hive? What is the exact dilution effect as bees feed on multiple fl owers? How does the quick turnover rate of bees affect the levels accumulated in the hive? Many of these questions are still unanswered and can only be established experimentally.
Conclusion
I would like to conclude this article with some important considerations. It is clear that neonicotinoids are toxic to bees at certain doses (lethal dose). However, the levels found in an agricultural setting are far lower than the lethal doses. Only with certain applications of neonicotinoids (eg, used as a foliar spray) may the levels bees are exposed to reach lethal doses, and hence we should refrain from this way of applying these pesticides.
Another important uncertainty is the link between levels in the plant (pollen
Figure 4. Nectar collection from an oilseed rape fl ower
and nectar) and levels inside the hive. This is unknown at the moment but this knowledge is desperately needed. The question is not so much what the levels of these neonicotinoids are in the plant but, more precisely, what is the exposure of bees to these neonicotinoids? Residual levels in the plant may be high but if exposure is nil, bees would not be affected by it. ♠
Footnote
1 The fi nal discussion is available as a webcast at
http://www.youtube.com/ watch?v=6pbCGDWed68
Further Reading
Blacquière, T, Smagghe, G, Van Gestel, CAM, Mommaerts, V (2012). Neonicotinoids in bees: A review on concentrations, side-effects and risk assessment. Ecotoxicology, 21, 973–992.
Tanner, G, Czerwenka, C (2011). LC-MS/MS analysis of neonicotinoid insecticides in honey: and residue fi ndings in Austrian honeys. Journal of Agricultural and Food Chemistry, 59, 12271−12277.
Godfray, HCJ, Blacquière, T, Field, LM, Hails, RS, Petrokofsky, G, Potts, SG, Raine, NE, Vanbergen, AJ, McLean, AR (2014). A restatement of the natural science evidence base concerning neonicotinoid insecticides and insect pollinators. Proceedings of the Royal Society B, 281: 20140558.
http://dx.doi.org/10.1098/ rspb.2014.0558
Hopwood, J, Vaughan, M, Shepherd, M, Biddinger, D, Mader, E, Hoffman Black, S, Mazzacano, C (2012). Are Neonicotinoids Killing Bees? A Review of Research into the Effects of Neonicotinoid Insecticides on Bees, with Recommendations for Action. The Xerces Society for Invertebrate Conservation.
Acknowledgements
British Beekeepers’ Association (BBKA) (David Aston and Pam Hunter), Keele University (Dr William Kirk and PhD student Kris Wisniewski).
May 2015 Vol 97 No 5
Diagram courtesy Kris Wisniewski
Photo courtesy Simon Croson
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48