Pesticide risk during commercial apple pollination is greater for honeybees than other managed and wild bees.
Abstract
Most pesticide research has focussed on risk to managed honeybees, but other managed and wild bees are also exposed to pesticides. Critically, we know little about the magnitude and sources of risk to honeybees compared with other bees during crop pollination. To compare pesticide exposure and risk across wild and managed bees, we sampled the main bee groups present during bloom in 20 apple orchards, including managed honeybees (Apis mellifera), managed bumblebee workers (Bombus impatiens), wild mining bees (Andrena spp. and Andrena [Melandrena] spp.), bumblebee foundress queens (Bombus impatiens) and eastern carpenter bees (Xylocopa virginica). We screened all bees for 92 pesticides and computed a Risk Quotient using available toxicity data (honeybee LD50s), adjusting for differences in toxicity known to scale with body mass. To gain insight into exposure origin, we compared residues in bees to those in focal orchard apple and dandelion flowers. Nearly all bee samples contained pesticides (95%), with the average contamination level ranging from 7.1 ± 2.8 parts per billion (ppb) in B. impatiens workers to 388.4 ± 146.2 ppb in Andrena. Exposure profiles were similar for all bees except A. mellifera, whose unique exposure profile included high levels of the neonicotinoid insecticide thiamethoxam. All bee groups except wild B. impatiens queens had at least one sample exceeding a US Environmental Protection Agency or European Food Safety Authority exposure level of concern. Apis mellifera experienced significantly greater risk than other bee groups, with 63% and 81% of samples exceeding an acute or chronic exposure level of concern, respectively. Risk to honeybees was driven primarily by high thiamethoxam levels not found in focal orchard flowers and likely originating outside the orchard. Synthesis and applications: We find that pesticide exposure and risk differ between honeybees and other managed and wild bees during apple pollination. Furthermore, pesticide exposure is a landscape-scale phenomenon and therefore measures to reduce exposure must consider the surroundings beyond focal farms. Limiting orchard sprays, while reducing on-farm exposures, will not protect far-foraging bees from off-farm exposures such as thiamethoxam, which we hypothesize is coming from nearby seed-treated corn fields planted during apple bloom.