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International audience; Information on honeybee foraging performance and especially bee loss rates at the colony level are crucial for evalu- ating the magnitude of effects due to pesticide exposure, thereby ensuring that protection goals for honeybee colonies are met (i.e. threshold of acceptable effects). However, current methods for monitoring honeybee foraging activity and mortality are very approximate (visual records) or are time-limited and mostly based on single cohort analysis. We therefore assess the potential of bee counters, that enable a colony-level and continuous monitoring of bee flight activ- ity and mortality, in pesticide risk assessment.After assessing the background activity and bee loss rates, we exposed colonies to two concentrations of sulfoxaflor (a neurotoxic insecticide) in sugar syrup: a concentration that was considered to be field realistic (0.59 μg/ml) and a higher concentration (2.36 μg/ml) representing a worst-case exposure scenario. We did not find any effect of the field-realistic concentration on flight activity and bee loss rates. However, a two-fold decrease in daily flight activity and a 10-fold increase in daily bee losses were detected in colonies exposed to the highest sulfoxaflor concentration as compared to before exposure. When compared to the theoretical trigger values associated with the specific protec- tion goal of 7 % colony-size reduction, the observed fold changes in daily bee losses were often found to be at risk for colonies. In conclusion, the real-time and colony-level monitoring of bee loss rates, combined with threshold values indicating at which levels bee loss rates threaten the colony, have great potential for improving regulatory pesticide risk assessments for honeybees under field conditions.

To ensure the optimal development of brood, a honeybee colony needs to maintain its temperature within a certain range of values (thermoregulation), regardless of environmental changes in biotic and abiotic factors. While the set of behavioural and physiological responses implemented by honeybees to regulate the brood temperature has been well studied, less is known about the factors that may influence the efficiency of this thermoregulation. Based on the response threshold model of task allocation, increased colony homeostasis should be driven by increases in group size. We therefore determined whether colony size (number of adult bees and amount of brood), positively influenced the efficiency of thermoregulation that we measured via two criteria: (i) the precision of the temperature close to its brood optimum, and (ii) the stability of the temperature around this optimum value. Finally, within the applied perspective of honeybee colony monitoring, we assessed whether the efficiency of thermoregulation could be used as a proxy of colony size. For that purpose, we followed 29 honeybee colonies over two years, measured both brood and adult population size regularly over the beekeeping season, and monitored the in-hive temperature over the 24 hours preceding the inspections of these colonies. We then studied the effect of the size of the colony (number of adult bees and number of brood cells), as well as meteorological variables, on the efficiency of thermoregulation (mean and stability of brood temperature, i.e. between 32 and 36°C). In addition to a clear link with meteorological conditions, we found that the mean brood temperature and the stability of this temperature were both positively linked to the size of colonies. The mean brood temperature was more dependent on the amount of the brood, while its stability was more dependent on the number of bees. However, these relationships between colony size and thermoregulation were too weak for clearly discriminating colony population size based solely on the brood thermoregulatory efficiency. This demonstrates an extremely high flexibility and efficiency of honeybee colonies to thermoregulate the brood regardless of the amount of brood and the group size.

Multiple global change pressures, and their interplay, cause plant-pollinator extinctions and modify species assemblages and interactions. This may alter the risks of pathogen host shifts, intra- or interspecific pathogen spread, and emergence of novel population or community epidemics. Flowers are hubs for pathogen transmission. Consequently, the structure of plant-pollinator interaction networks may be pivotal in pathogen host shifts and modulating disease dynamics. Traits of plants, pollinators, and pathogens may also govern the interspecific spread of pathogens. Pathogen spillover-spillback between managed and wild pollinators risks driving the evolution of virulence and community epidemics. Understanding this interplay between host-pathogen dynamics and global change will be crucial to predicting impacts on pollinators and pollination underpinning ecosystems and human wellbeing.