Modelling honeybee foraging in complex landscapes and consequences for exposure to pesticides in the bee hive

Within the recent EFSA guidance document on the risk assessment of plant
protection products on bees [1], the risk assessment for the consumption of nectar and pollen in the hive is based on the conservative approach that bees forage exclusively on one type of plant. The guidance gives options to replace this conservative with a more realistic approach considering foraging on all attractive plants in the foraging area at the landscape level and presents a simple model approach that assumes that the fraction of honey bees foraging in each field within a certain maximum foraging radius, is proportional to the product of attractiveness (e.g. defined by nectar yield) and area of each field. We implemented a spatially explicit version of the parsimonious EFSA model. In addition, we developed a mechanistic, energetics-based foraging model as an alternative. By quantifying foraging costs and yield in terms of energy [2], we can account for the impact of field distance and size, the occurrence of resource depletion and the characteristics of the resource type (crops and wild flowers) like seasonal and diurnal patterns in availability. Both spatially-explicit models used detailed GIS data for crop coverage and distribution of potentially nectar-providing off-crop habitats in the Netherlands. We tested the models with an artificial test landscape and calculated dilution factors for all possible bee hive positions in the landscape. The set of resulting dilution factors was analysed and statistical descriptors such as median values or percentiles were extracted.