A mechanistic model to assess risks to honeybee colonies from exposure to pesticides under different scenarios of combined stressors and factors

A conceptual model for the risk assessment of pesticides in a single honeybee colony under different scenarios was developed. The model is composed of different modules. A base model representing the honeybee colony (the Colony, the in-Hive Products and the Foraging modules), placed within a complex landscape (the Resource Providing Unit and Environmental Drivers modules) and the inclusion of multiple factors and stressors on colony health (the Pesticides module, the Biological Agents module and the Beekeeping Management Practices module). The in-hive products comprise pollen and beebread, nectar and honey, water, jelly and wax. The foraging module is linked to the colony (food stores), resource-providing unit (availability of resources in terms of protein and sugar amounts) and environmental drivers. It is based on forager decisions (to fly or not and to collect nectar, pollen or water). The Pesticides module includes exposure (both outside and in-hive) to pesticides and effects in bees (queen, larvae and pupae of drones and workers, nurses and other inhive bees, foragers and winter bees). Scenarios comprise different landscapes, weather and climatic conditions, some biological agents and beekeeping management practices having an influence on the dynamics of the colony and in-hive products. The spatial scale is 3 km around the hive and the spatial resolution is 1 m2. The temporal scale is 1 year corresponding to one colony annual cycle and the temporal resolution ranges from hours (e.g. inflow of pollen/nectar/pesticides) to days (in-hive processes). Recommendations were made for the development of the conceptual model presented in this report into a mechanistic model to assess the risk of pesticides on honeybee colony health in complex landscapes and in the presence of multiple stressors. Finally, new opportunities for further model implementations were highlighted.