New study in Nature - Scientific Reports finds strong evidence for pesticide + pathogen hypothesis as key explanation for bee disorders.
ABSTRACT: In ecosystems, a variety of biological, chemical and physical stressors may act in combination to induce illness in populations of living organisms. While recent surveys reported that parasite-insecticide interactions can synergistically and negatively affect honeybee survival, the importance of sequence in exposure to stressors has hardly received any attention. In this work, Western honeybees (Apis mellifera) were sequentially or simultaneously infected by the microsporidian parasite Nosema ceranae and chronically exposed to a sublethal dose of the insecticide fipronil, respectively chosen as biological and chemical stressors. Interestingly, every combination tested led to a synergistic effect on honeybee survival, with the most significant impacts when stressors were applied at the emergence of honeybees. Our study presents significant outcomes on beekeeping management but also points out the potential risks incurred by any living organism frequently exposed to both pathogens and insecticides in their habitat.
Conclusion of the study:
In conclusion, our findings showed that honeybees co-exposed to the natural stressor N. ceranae and to an environmental concentration of the insecticide fipronil will undergo a significantly higher mortality compared to the sum of the effects induced by each agent acting alone.
Few studies have been done on such interactions in the honeybee and the resulting data illustrate the difficulty to find out the synergy related mechanisms. The economical and ecological value of honeybees renders our results worrying as the scenario of colonies housing both N. ceranae spores and insecticide residues is realistic. Those results also point out the potential risks incurred by any living organism frequently exposed to both pesticides and pathogens in their environment, no matter the sequence of exposure to those agents. Such multiple stressors interactions, endangering honeybees and potentially other communities, deserve additional attention. Finally, understanding the complexity of cumulative risks is a prerequisite for the implementation of more efficient guidelines in the frame of future chemicals regulation.
Julie Aufauvre, David G. Biron, Cyril Vidau, Regis Fontbonne, Mathieu Roudel, Marie Diogon, Bernard Vigues, Luc P. Belzunces, Frederic Delbac & Nicolas Blot, 2012. Parasite-insecticide interactions: a case study of Nosema ceranae and fipronil synergy on honeybee, Nature - Scientific Reports, 2, 326.
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The Telegraph 22 March 2012 on this study: