Let me bee... I'm no pest!
Over the last few years bee populations have been declining worldwide. Last year the number of honeybee colonies in the UK fell by 34%, nearly double that of previous years1. The main causes for the decline are unclear, with possible causes listed as; poor weather, disease, varroa parasites, pesticides or a combination of all these.
Researchers at Dundee University are looking into the possible causes of bee population decline. Their novel method, published in Nature Protocol Exchange, "Patch-clamp recording from Kenyon cells in acutely-isolated bee brain"2 has allowed them to study the effect of cholinergic pesticides on the intact honeybee brain. Their research paper, "Cholinergic pesticides cause mushroom body neuronal inactivation in honeybees", published in Nature Communications, March 20133.
Mushroom bodies are important insect brain structures that mediate multisensory integration, learning and memory. Kenyon cells are the major cells of the honeybee mushroom body, with mainly cholinergic synaptic inputs. Commonly, studies of neurotransmitter receptor function in bees are carried out using cultured neurons. However the development of a protocol to record from intact bee brain tissue was essential for investigating the effect of neonicotinoid pesticides on Kenyon cell activity. The procedure uses Scientifica's PatchStar micromanipulator to position recording electrodes with submicron accuracy; then retain the position for long-term recordings of up to several hours.
The study found that non-lethal levels of cholinergic pesticides (i.e. imidacloprid and clothianidin) depolarised Kenyon cells in the honeybee mushroom bodies, by activating nicotinic receptors. This caused a transient increase in excitability followed by sustained depolarisation, blocking the cells activity. Interestingly the group also found that coumophos oxon, the miticide often used to treat varroa mite infestation in beehives, causes a similar disruption of Kenyon cell function by inhibiting the breakdown of acetylcholine. These findings provide a neuronal explanation for the observed changes to honeybee learning and foraging behaviours following exposure to cholinergic pesticides.
In a bid to curb the decline in bee colonies, earlier this year the EU restricted the use of neonicotinoid pesticides; imidacloprid, clothianidin, and thiamethoxam. At the time the UK government voted against this move, arguing more research was needed and bans may push farmers back to using more harmful pesticides. Now, Palmer et al. have shown that imidacloprid, clothianidin and coumaphos oxon are potent neuromodulators in honeybee brain. In particular the group stress that the use of miticides such as coumaphos may pose a greater risk to honeybee health, because of high exposure levels, and suggests using alternative methods for removing Varroa from a hive.
References:
1 – British Honey Bee Association: http://www.bbka.org.uk/
2 - Palmer, M., Moffat, C., Saranzewa, N., Harvey, J., Wright, G.A., & Connolly, C.N. (2013) "Cholinergic pesticides cause mushroom body neuronal inactivation in honeybees" Nature Communications: DOI: 10.1038/ncomms2648
http://www.nature.com/ncomms/journal/v4/n3/full/ncomms2648.html
3 - Palmer, M. & Connolly, C.N. (2013) "Patch-clamp recording from Kenyon cells in acutely-isolated bee brain" Nature Protocol Exchange: DOI: 10.1038/protex.2013.038
http://www.nature.com/protocolexchange/protocols/2664
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