Effects of heavy metal accumulation mediated by floral rewards on key stages of growth and development of bumblebees (Bombus terrestris L.)

Whether soil heavy metal pollution contributes to the decline in pollinator populations remains inconclusive. Based on the detection of heavy metals in the nectar, pollen, and bodies of pollinating insects in areas affected by heavy metal pollution, this study aimed to investigate the impact of adding four heavy metals-zinc (Zn), lead (Pb), copper (Cu), and nickel (Ni)-at realistic concentrations to the diet on the pre-oviposition period, larval development period, production of adult bees, and weight of worker bees. The study sought to evaluate the influence of heavy metal accumulation mediated by floral rewards on key stages of growth and development of bumblebee (Bombus terrestris L.). Results revealed that Zn, Pb, and Cu significantly extended the pre-oviposition period of queen bees, with Pb doubling the time at high concentrations and Ni showing no significant effect at moderate to low concentrations. Lead, Cu, and Ni significantly extended the larval development period at medium and high concentrations, whereas Zn only had a significant effect at high concentrations. The four heavy metals significantly reduced the adult bee yield and the body weight of worker bees at different concentrations, among which the high concentrations of Pb and Cu significantly reduced the adult bee yield by 25%-40%. The effect of a high concentration of copper on the body weight of worker bees was the most obvious, a reduction by 30%. Our findings support the hypothesis that heavy metal pollution, mediated by floral rewards, can have serious impact on some key stages of growth and development of bumblebees.