International Union for the Study of Social Insects (IUSSI2018), August 5-10, 2018 in Guarujá, Brazil.

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Synergistic effects of parasitism and pesticide exposure on honey bee (Apis mellifera) survival and immunity

Author(s):
Shannon Holt, Julia Grassl , Naomi Cremen , Marianne Peso , Dorothee Hahne , Boris Baer
Institution(s):
Honey Bee Health Research Group, ARC Centre of Excellence in Plant Energy Biology, School of Molecular Sciences, University of Western Australia, Australia; Honey Bee Health Research Group, ARC Centre of Excellence in Plant Energy Biology, School of Molecular Sciences, University of Western Australia, Australia ; ARC Centre of Excellence in Plant Energy Biology, School of Molecular Sciences, University of Western Australia, Australia ; ARC Centre of Excellence in Plant Energy Biology, School of Molecular Sciences, University of Western Australia, Australia ; UWA Centre for Metabolomics, Metabolomics Australia, University of Western Australia, Australia ; Centre for Integrative Bee Research (CIBER), Department of Entomology, University of California Riverside, ARC Centre of Excellence in Plant Energy Biology, School of Molecular Sciences, University of Western Australia, Australia
The substantial losses reported in native and managed insect pollinator populations have resulted in widespread concern, given their importance for human food production and ecosystem stability. Several factors have been studied as possible causes of observed declines in pollinator health, such as parasites, exposure to agricultural pesticides, habitat loss and climate change. More recently, a combination of these factors rather than a single cause have been hypothesised as drivers of pollinator losses, but the study of such interactions are challenging in the field because of confounding environmental factors. We examined the impact of single and combined stressors in a generally healthy Australian population of honey bees (Apis mellifera). To do this we exposed workers and drones to the neonicotinoid insecticide Thiamethoxam, the fungal gut parasite Nosema apis or both stressors at the same time and found that simultaneous exposure significantly reduced bee health. In workers we found a substantial increase in mortality and a reduction of immunocompetence in the surviving individuals. In males, we found that the vast majority of males did not survive to sexual maturity after an exposure to Thiamethoxam at concentrations more than 20 times lower compared to those measured in the field. Such decrease in reproductive success of colonies will also impact gene flow and genetic diversity at the population level, which are both known as key components of pollinator health. We conclude that the exposure of generally healthy bees to multiple environmental stressors results in synergistic effects that are expected to negatively impact performance and could be sufficient to eventually trigger colonies to collapse.
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