Exposing honeybees to both parasites and insecticides has a greater negative effect on survival rates than expected, given the individual impact of each agent. This synergistic effect occurs whether the bees are exposed to the two stressors sequentially or simultaneously, a paper in Scientific Reports suggests. The study highlights potential risks incurred by living organisms that are frequently exposed to both pesticides and pathogens in their environment, regardless of the sequence of exposure.
In the environment, living organisms are exposed to a range of stressors, some biological and some non-biological. The interactions between multiple stressors are thought to have a synergistic effect on organisms - a greater effect than expected from the cumulative individual exposures. But it has remained unclear whether these effects are dependent on the sequence of application of the two types of stressor.
Nicolas Blot and colleagues from the Laboratoire Microorganismes: Genome et Environnement investigated this issue, using the Western honeybee (Apis mellifera), which are frequently co-exposed to both parasites and insecticides and which are valuable economically and ecologically. The bees were infected by the microsporidian parasite Nosema ceranae and exposed to a sub-lethal dose of fipronil, a broad-spectrum insecticide, either sequentially or simultaneously. The authors found that every combination tested had a synergistic effect on honeybee survival. These findings could prove useful for researchers working in ecology, parasitology and crop production.