Traces of Imidacloprid induce precocious foraging and reduce foraging performances in honey bees

Authors: COLIN, THEOTIME - Macquarie University; Meikle, William; WU, XIAOBO - Jiangxi Agricultural University; BARRON, ANDREW - Macquarie University

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2019
Publication Date: 7/1/2019
Citation: Colin, T., Meikle, W.G., Wu, X., Barron, A. 2019. Traces of Imidacloprid induce precocious foraging and reduce foraging performances in honey bees. Environmental Science and Technology. 53(14):8252-8261. https://doi.org/10.1021/acs.est.9b02452.
DOI: https://doi.org/10.1021/acs.est.9b02452

Interpretive Summary: Currently there is a great deal of concern about the impact of pesticides on honey bee health and behavior. Bees are often exposed to very low concentrations of pesticides. Low concentrations usually do not kill bees, but they might change bee behavior, the way some compounds can change human behavior at low concentrations. In this study one group of honey bee larvae (immature bees) was exposed to very low (5 parts per billion) concentrations of a neonicotinoid pesticide mixed in sugar syrup, while another group was given pure sugar syrup. After the bees matured into adults, small electronic tags were placed on their backs and bee movement was monitored in and out of the hive. Bees that were fed the pesticide had 28% fewer foraging flights compared to control bees. With fewer foraging flights per bee, more bees need to forage, and that might upset the colony population dynamics. Understanding these effects is important for making sound decisions on pesticide policy.

Technical Abstract: There is increasing worldwide concern about the impacts of pesticide residues on honey bees and bee colony survival, but how sublethal effects of pesticides on bees might cause colony failure remains highly controversial, with field data giving very mixed results. To explore how trace levels of the neonicotinoid pesticide imidacloprid impacted colony foraging performance, we equipped bees with RFID tags that allowed us to track their lifetime flight behavior. One group of bees was exposed to a trace concentration (5 µg/kg, ppb) of imidacloprid in sugar syrup while in the larval stage. The imidacloprid residues caused bees to start foraging when younger as adults and perform fewer orientation flights, and reduced their lifetime foraging flights by 28%. The magnitude of the effects of a trace imidacloprid concentration delivered only during larval stage highlights the severity of pesticide residues for bee foraging performance. Our data suggest that neonicotinoids could impact colony function by imbalancing the normal age based division of labor in a colony and reducing foraging efficiency. Understanding this mechanism will help the development of interventions to safeguard bee colony health.