Chemical residues in declining commercial honey bee colonies

Following heightened colony losses, we screened 132 colonies from 23 commercial beekeeping operations in the states of Florida and California. We assessed chemical residues, finding beekeeper-applied miticides, followed by fungicides, were in the highest prevalence and concentration in all colony matrices. Insecticides comprised a minority of detections and concentration. Due to their heightened toxicity, insecticides contributed substantially to hazard quotients with one residue, the neonicotinoid imidacloprid, contributing 99.9% to overall HQ. We found both high prevalence and high levels of imidacloprid in adult bee bodies. Additionally, we preserved a small subsample of dying bees. Our findings highlight a survivorship bias, where dying bees had active ingredients known to have acute toxicity to bees. This result mirrors recent evidence for viral drivers of bee declines that were missed in whole-colony surveys. While bees die from multiple, often interacting, stressors, here we show single contributors at levels capable of causing acute harm.