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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Bee Research Laboratory » Research » Publications at this Location » Publication #320695
Title: Assessment of chronic sublethal effects of imidacloprid on honey bee colony health

Author
item DIVELY, GALEN - University Of Maryland
item EMBREY, MICHAEL - Environmental Protection Agency (EPA)
item KAMEL, ALAA - Environmental Protection Agency (EPA)
item HAWTHORNE, DAVID - University Of Maryland
item Pettis, Jeffery

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2015
Publication Date: 11/30/2015
Citation: Dively, G.P., Embrey, M.S., Kamel, A., Hawthorne, D.J., Pettis, J.S. 2015. Assessment of chronic sublethal effects of imidacloprid on honey bee colony health. PLoS One. doi: 10.1371/journal.pone.0118748.

Interpretive Summary: Pesticides could affect honey bee health. This three-year study looks at the residues of the pesticide, imidacloprid within a honey bee colony (wax, pollen, honey) and determines the chronic sublethal effects these residues have on a honey colony when they are fed a diet of pollen containing the pesticide. The colonies exposed to the pesticide did have higher rates of queen loss and broodless periods later in the summer which led to the colonies being weaker in the winter. Chronic exposure to the pesticide in the higher doses could cause negative impacts on honey bee colony health and reduce winter survival, but exposure in lower doses had little or no effect on colony health and it is not likely the sole cause of colony declines. This information will help beekeepers manage their colonies.

Technical Abstract: Here we present results of a three-year study to determine the fate of imidacloprid residues in hive matrices and to assess chronic sublethal effects on whole honey bee colonies fed supplemental pollen diet containing imidacloprid at 5, 20 and 100 µg/kg over multiple brood cycles. Various endpoints of colony performance and foraging behavior were measured during and after exposure, including winter survival. Imidacloprid residues became diluted or non-detectable within colonies due to the processing of beebread and honey and the rapid metabolism of the chemical. Imidacloprid exposure doses up to 100 µg/kg had no significant effects on foraging activity or other colony performance indicators during and shortly after exposure. Diseases and pest species did not affect colony health but infestations of Varroa mites were significantly higher in exposed colonies. Honey stores indicated that exposed colonies may have avoided the contaminated food. Imidacloprid dose effects was delayed later in the summer, when colonies exposed to 20 and 100 µg/kg experienced higher rates of queen failure and broodless periods, which led to weaker colonies going into the winter. Pooled over two years, winter survival of colonies averaged 85.7, 72.4, 61.2 and 59.2% in the control, 5, 20 and 100 µg/kg treatment groups, respectively. Analysis of colony survival data showed a significant dose effect, and all contrast tests comparing survival between control and treatment groups were significant, except for colonies exposed to 5 µg/kg. Given the weight of evidence, chronic exposure to imidacloprid at the higher range of field doses (20 to 100 µg/kg) in pollen of certain treated crops could cause negative impacts on honey bee colony health and reduced overwintering success, but the most likely encountered high range of field doses relevant for seed-treated crops (5 µg/kg) had negligible effects on colony health and are unlikely a sole cause of colony declines.