March 27, 2013

expert reaction to insecticides on the honey bee brain

Research in Nature Communications detailed an underlying cellular mechanism for the neuronal dysfunction in the honeybee brain caused by some types of pesticides, including neonicotinoids and organophosphates.

Prof Francis Ratnieks, Professor of Apiculture at the University of Sussex, said:

“This is an interesting piece of work which adds to our understanding of how insecticides affect part of the honey bee brain.  The authors are careful not to oversell their results in terms of declines in bees, or the effects of neonicotinoid insecticides in bee decline.

“One of the chemicals tested was coumaphos. This has been used in the USA as a control agent against Varroa mites in the formulation CheckMite+.  But my contacts in the USA tell me that it is not widely used any more due to the mites becoming resistant.  Coumaphos is not legal for use in the UK or EC to control Varroa mites.

“Whenever lab work on the possible effects of pesticides on bees is done, the researchers have to choose appropriate doses, and should ideally work with a series of doses.  The researchers report that ‘Imidacloprid levels of up to 28 p.p.b. have been detected in plant flowers and nectar’.  However, it seems that typical concentrations, such as in the nectar of oil seed rape, are in reality lower than this.  Cresswell (2011) reviewed numerous studies on the effect of imidacloprid on honey bees and states: ‘the field-realistic range of imidacloprid concentrations is assumed to be 0.7–10 micrograms per litre’. Cresswell also comments that oilseed rape has lower levels. 

[Cresswell J. E. 2011. A meta-analysis of experiments testing the effects of a neonicotinoid insecticide (Imidacloprid) on honey bees. Ecotoxicology 20: 149-157.]

“Bees are wonderful creatures in their own right, and are of increasing importance to our own food supply through pollination.  This makes it extremely important that we understand what affects their health and causes declines in their populations.  It’s no surprise that insecticides at high concentrations are harmful, but we don’t know whether the low levels of neonicotinoid insecticides in the nectar and pollen of treated plants, such as oil seed rape, are harmful in the real world. 

“Bee populations in the UK have been declining for a lot longer than neonicotinoid insecticides have been used.  It’s not as though we don’t have other potential causes for the declines.  The intensification of farmland, which covers 75% of Britain, is probably the most important.  This has significantly reduced the numbers of flowers and habitats for wildlife.  Practically any type of wildlife you care to name is in decline in Britain: reptiles, amphibians, birds, butterflies, moths, bumble bees, honey bees, wild flowers.

“This new research gives us basic knowledge of how these insecticides affect specific cells in the honey bee brain that play a role in honey bee learning and behaviour.  It should be remembered that insecticides are supposed to kill insects, and many of them, including those studied here, kill via effects on the nervous system.  In terms of the overall effect of neonicotinoid insecticides on bee health and bee populations, the jury is still out.  In particular, we do not know enough about the actual amounts contacted by bees as they forage and the degree to which this may result in fewer bees.

“One potential worry in the use of insecticides is that two or more may ‘synergise’; that is, combine to have an effect that is disproportionately bad on a non-target organism like a bee.  The authors state that the effects of treating bee brain with multiple chemicals ‘are additive with combined application’.  That is, the effect is not synergistic.”

‘Cholinergic pesticides cause mushroom body neuronal inactivation in honeybees’ by Mary J. Palmer et al., published in Nature Communications on Wednesday 27th March.