Cadmium Contaminants in Pollen and Nectar Are Variably Linked to the Growth and Foraging Behaviors of Honey Bees

Cadmium (Cd) is a heavy metal present in pollen and nectar that affects pollinator attributes. Honey bees possess the ability to eliminate Cd from honey. Consequently, the concentration of Cd in pollen, rather than nectar, is the critical factor influencing the growth and foraging behavior of honey bees. However, there is a dearth of studies regarding the specific association by which the impact on bee growth and foraging behavior fluctuates in relation to the Cd dosage of pollen or nectar. We hypothesized that at low exposure levels, the amount of Cd in pollen would affect honey bee growth, and the amount of nectar influences honey bee foraging behavior. At high exposure levels, the amount of Cd in pollen and nectar would affect both honey bee growth and foraging behavior. A field experiment was performed in Sichuan (the average background value of Cd in soil is 5.6 times higher than other regions in China) to examine the impact of different soil Cd concentrations (low: 0.60 ± 0.05 mg·kg^-1 (average ± SD); middle: 1.32 ± 0.08 mg·kg^-1; high: 1.76 ± 0.10 mg·kg^-1) on the Cd levels in plant organs (<i>Brassica campestris</i>), alongside the body mass and visitation rates of honey bees (<i>Apis mellifera</i>). Our results indicated in honey bees in the habitats with low concentrations of soil Cd that the Cd content in pollen was inversely correlated with the body mass of larvae, pupae, and worker bees. The quantity of nectar governed the foraging activity of honey bees in the habitats with low levels of soil Cd. At middle to high exposure levels, Cd concentrations in pollen and honey exerted a negative influence on honey bee development and foraging behavior. These findings offer novel insights into the impact of Cd on pollinator attributes, and the global decline of pollinators.