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Honeybee with RFID chip. © INRA, Laurent Guilbaud

Neonicotinoid insecticides and bees: disorientation in individual bees, strategic adaptation by colony, confirmed in field trials

A new field trial has confirmed laboratory tests to study the risk of disorientation in bees exposed to thiamethoxam, used to treat colza seeds. The study reveals that proximity to sprayed plots reduces life expectancy in foraging bees. Bee colonies respond to this high death rate by adapting comb production to favour the replacement of worker bees. These findings pave the way towards new research to assess toxicological risks in the field.  The study, conducted by INRA, Terres Inovia, CNRS, ITSAP-Institut de l’abeille and ACTA, was published on 18 November 2015 in the Proceedings of the Royal Society B.

Updated on 12/18/2015
Published on 11/20/2015
Keywords: PESTICIDE - BEE

The study was conducted following a double recommendation by the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) based on initial findings published in 2012 (Henry et al.*) concerning the toxic effects of neonicotinoid insecticides. The first was to confirm whether or not the practice of coating seeds with certain insecticides had an impact on honeybee mortality in real field conditions; the second was to specify effects on colony performance (this data was not usually included in previous studies).

For the purpose of the full-scale experiment, researchers attached RFID microchips to 7,000 bees in order to monitor their comings and goings to/from the hive. Bees were able to forage in 200 square kilometres of farm land which included a number of colza fields where seeds had been treated with thiamethoxam, a neonicotinoid insecticide. Results show that the risk of bee mortality increases in relation to hive exposure. The gradient of exposure is a combination of field size and distance from the hive. Exposure effects gradually increased as the flowering period of the colza progressed, with an average risk of mortality ranging between 5 and 22%.

Scientists did not observe any changes in hive performance, however. Honey production was not affected by the gradient of exposure to crops from seeds treated with insecticide. The findings suggest that demographic regulation mechanisms may operate within the hive colony to compensate the higher individual death rate. The colonies studied maintained sufficient populations of worker bees to ensure a continued rate of honey production. Thus, differences in the size of male combs and worker bee combs evened out during flowering season and in the weeks that followed.  

Trace amounts of imidacloprid – another neonicotinoid used only in non-pollinated crops – were also detected in most nectar samples taken from colza blossoms, as well as in the nectar collected by foraging bees. Because the study was initially designed to study the effects of thiamethoxam alone, this simultaneous exposure makes it more difficult to assess field risks, as scientists were unable to distinguish individual effects of each insecticide on the bees.

By shedding light on the complex biological mechanisms involved, this study highlights the difficulty of measuring with precision the risks bees face in real conditions of insecticide exposure. Such risks are measurable on a large spatial scale and imply lagged biological effects on hives that are currently not given attention by health authorities.

The authors confirm the importance of measuring the chronic effects of low doses in assessments of pesticide toxicity prior to their release on the market, as well as the possible existence of cumulative effects between different active substances.

*Ex.: Henry M, Béguin M, Requier F, Rollin O, Odoux J-F, Aupinel P, Aptel J, Tchamitchian S, Decourtye A. (2012). A common pesticide decreases foraging success and survival in honey bees. Science 336, 348–350. (doi:10.1126/science.1215039)

Reference

Mickaël Henry, Nicolas Cerrutti, Pierrick Aupinel, Axel Decourtye, Mélanie Gayrard, Jean-François Odoux, Aurélien Pissard, Charlotte Rüger, Vincent Bretagnolle. Reconciling laboratory and field assessments of neonicotinoid toxicity to honeybees. Proceedings of the Royal Society B, 18 November 2015. DOI:10.1098/rspb.2015.2110

Contact(s)
Scientific contact(s):

Press Relations:
INRA News Office (33 (0)1 42 75 91 86)
Associated Division(s):
Plant Health and Environment
Associated Centre(s):
Provence-Alpes-Côte d'Azur

Full-scale experiment

Tests were conducted over a 200 square kilometre area in which certain colza fields were treated by coating seeds with thiamethoxam. Because this practice was banned in France in 2012 as a precautionary measure, authorisation from the French Ministry of Agriculture was required. In total, in 2013 and 2014, 280 ha (41 fields) of colza was grown from coated seeds. Eighteen experimental hives free of any parasite- or disease-related symptoms were also distributed in this area, with care taken to create various gradients of exposure with the fields. In this full-scale test environment, the lives of 7,000 bees were followed using RFID microchips which were glued to their backs. Researchers installed electronic sensors at the entrances to the hives to study bee life expectancy in relation to the bees’ exposure to the treated crops.

This experiment was initially launched by Terres Inovia as part of a broad partnership between INRA, CNRS, ITSAP-Institut de l’abeille and ACTA, and conducted as part of the ECOBEE initiative at the Plaine & Val de Sèvre study area near Niort in western France. (http://www.za.plainevalsevre.cnrs.fr).