Last year I spent a significant amount of time looking into neonicotinoid pesticides and their effects on bees through agricultural use for my dissertation. I found it fascinating but in hindsight it was probably far too big a topic for the project, especially in the way I had to write it. So I thought I’d briefly go over it and then possibly put more in depth posts regarding it and future developments in later posts.
Bees are brilliant creatures; with many different species they are one of the most prominent pollinating insects in the world. They are not alone in being useful pollinators but they are seen as being of great importance to agriculture with around 80% of crops in Europe benefiting from some interaction with bee species.
Neonicotinoid pesticides, also known as chloroncotinyls, are a range of systemic pesticides first developed by Shell in the 80’s and later by Bayer and Syngenta in Europe. Designed to target the post-synaptic nicotinic acetylcholine receptors (nAChRs) located in the insects central nervous system. They are ubiquitous in agriculture due to their high toxicity to target species and limited effect on other species.
There have been many laboratory studies into the effect these pesticides have on bees with some varying results but some worrying results have been shown and linked to the process known as colony collapse disorder (CCD). CCD occurs when drones fail to return to the hive after foraging trips. There have also been other effects noted, such as a reduction in the production of queens in bumble bees (Bombus terrestris) after being dosed with imidacloprid as well as notable reduction in weight compared to the control group .
Honey bees (Apis mellifera) are by far the most studied species due to their importance with apiculture as well as agricultural pollination. In 2000 it was estimated the value of the agricultural yield enhanced by honey bee pollination was around $14.6 billion. This shows how important it is to understand how detrimental external factors can be on pollinators. The Proboscis Extension Response/Reflex (PER) assay is a test to indicate memory and learning due to the proboscis response to a stimulation of the antennae. In A. mellifera saw hits to learning performance and reflex responses in winter and summer bees .
In Brazil it has been shown that neonicotinoids directly affect the development of the area known as the mushroom body in the brain of native stingless bees (M. quadrifasciata anthidioides), this area is important for memory retention especially regarding the areas outside of the hive. This could lead to problems with the bees ability to return to the hive once it has flown a sufficient distance on foraging trips. It was also noted there was some effect on the walking behaviour of the bees after several days exposure with less steps being taken compared to the control groups.
As if these weren’t enough problems it is thought that disturbances to growth and larval development make bees susceptible to further indirect effects. Varroa mites are one of these issues, which have also been suggested as a prominent cause for CCD, it is believed due to the decreased size and extended period of development as a larvae allows the varroa mite a greater chance of attacking the young and reducing the size of the brood. A gut pathogen called Nosema ceranae has also been noted having an increase in occurrence with bees that have been exposed to pesticides and fungicides, including imidacloprid .
These are just a few examples of the studies looking at problems for bees. Because these studies are primarily done in a laboratory of severely restricted semi field tests it has been said that they are unrepresentative of the exposure bees receive in the wild, this is to an extent a valid point which was used to try and avoid a temporary ban on the pesticides by the EU last year in favour of increased field studies which they felt would prove a lack of connection between neonicotinoid pesticides and detrimental effects on bee populations.
A study by the Food and Environment Research Agency (FERA) which was used as a basis for the UK governments decision on whether to support a temporary ban pulled up a striking issue with plausibility of extensive field trials. During their experiments they noticed that the bees would travel for significant distances in attempts to forage for pollen even if there was a substantial supply right next to their hives, when examining the bees they discovered a variety of neonicotinoids and pesticides from several other fields in the control group which realistically invalidated the results. Essentially this would indicate without a ban on neonicotinoids for all but research it would be all but impossible to control the factors effectively enough to prove whether they were truly an issue to be tackled.
In the end I concluded that there is a definite need for further research, and the ban was essential to making that research effective. It is too important an issue to be left with poor and incomplete information to base decisions on, especially when the current research is not entirely conclusive. I’ll be looking forward to reading more over the coming months and years and writing further on the progress made in new studies.
1. Grimm, M., Sedy, K., Süßenbacher, E. & Riss, A., 2012. Existing scientific evidence of the effects of neonicotinoid pesticides on bees, Brussels: EU Directorate-General for internal policies.
2. Jeschke, P. & Nauen, R., 2008. Neonicotinoids – from zero to hero in insecticide chemistry. Pest Management Science, Volume 64, pp. 1084-1098.
3. Whitehorn, P., O’Connor, S., Wackers, F. & Goulson, D., 2012. Neonicotinoid pesticide reduces bumble bee growth and queen production. Science, Volume 336, pp. 351-352.
4. Morse, R. & Calderone, N., 2000. The value of honey bees as pollinators of U.S. crops in 2000. Bee culture.
5. Decourtye, A., Lacassie, E. & Pham-Delegue, 2003. Learning performances of honeybees (Apis mellifer L) are differently affected by imidacloprid according to season. Pest management science, Volume 59, pp. 269-278.
6. Tome, H.V.V. Martins, G.F. Lima, M.A.P. Campos, A.O. Guedes, R.N.C., 2012. Imidacloprid-induced impairment of mushroom bodies and behavior of the native stingless bee Melipona quadrifasciata anthidioides. PLoS ONE, 7(6).
7. Wu, J., Anelli, C. & Sheppard, W., 2011. Sub-lethal effects of pesticide residuses in brood comb on worker honey bee (Apis mellifera) development and longevity. PLoS ONE, 6(2).
8. Pettis, J.S. Lichtenberg, E.M. Andree, M. Stitzinger, J. Rose, R. vanEngelsdrop, D., 2013. Crop pollination exposes honey bees to pesticides which alters their succeptibility to the gut pathogen Nosema ceranae. PLOS ONE, 8(7).
9. Thompson, H. Harrington, P. Wilkins, S. Pietravalle, S. Sweet, D. Jones, A., 2013. Effects of neonicotinoid seed treatments on bumble bee colonies under field conditions, s.l.: The Food and Environment Research Agency.