Bee-yond capacity: how high colony densities challenge honey bee (Hymenoptera: Apidae) health in lowbush blueberries (Ericaceae)

Quebec is Canada’s leading producer of lowbush blueberries (Ericaceae), a crop reliant on honey bees (Hymenoptera: Apidae) for pollination. Intensive pollination services may adversely affect bee health. Few studies have examined the impact of increasing colony density and its carryover effects. This study compares control colonies used for honey production with colonies placed at two pollination densities (2.5 and 5 colonies/ha) in Saguenay–Lac-Saint-Jean over two years (2022–2023). Colonies were assessed at the start and end of pollination and one month later. We evaluated colony strength, Varroa destructor (Mesostigmata: Varroidae) infestation, pathogen loads (including Vairimorpha spp. (Nosematidae), and viruses such as deformed wing viruses A and B (Iflaviridae) and acute bee paralysis virus, Israeli acute paralysis virus, Kashmir bee virus, chronic bee paralysis virus, and black queen cell virus (all Dicistroviridae), and pesticide residues. Pollination was associated with reduced colony strength gain, higher proportions of colonies infested with Varroa , and increased deformed wing virus B loads. Colony strength was most affected by increased density in the carryover assessment. No pesticide levels exceeded bee toxicity thresholds in nectar and bee bread. This is the first study to evaluate colony density effects on honey bee health in lowbush blueberry systems.