Location: Carl Hayden Bee Research CenterTitle: Sublethal concentrations of clothianidin affect honey bee colony growth and hive CO2 concentration
Submitted to: Cold Spring Harbor Press
Publication Type: Pre-print Publication
Publication Acceptance Date: 1/19/2021
Publication Date: 6/5/2021
Citation: Meikle, W.G., Adamczyk Jr, J.J., Weiss, M., Ross, J.F., Werle, C.T., Beren, E.D. 2021. Sublethal concentrations of clothianidin affect honey bee colony growth and hive CO2 concentration. BioRxiv. https://doi.org/10.1101/2020.06.05.136127.
Interpretive Summary: Exposure of honey bees to pesticides is a primary concern of the agricultural industry in general and the beekeeping industry in particular. Acute exposure to high concentrations of pesticides can kill foragers and weaken and kill bee colonies. Exposure to low, sublethal concentrations of pesticides are different and more difficult to detect, because such exposure can cause changes in bee behavior rather than kill bees outright. Sublethal exposure to neonicotinoid pesticides can impair honey bee learning and sensory capabilities, decrease foraging success, and can have indirect effects on bees by acting as repellents, and bees exposed to neonicotinoid pesticides have been found to be more susceptible to diseases. In this study we exposed colonies to very low, but field realistic, levels of a neonicotinoid pesticide, clothianidin, in 3 field experiments: twice in Arizona, in successive years at the same site, and once in Mississippi. We evaluated colonies on a regular basis, put colonies on hive scales to constantly measure their weight, and put sensors inside to constantly measure their internal temperature. In one experiment we also measured their internal CO2 concentration. We did find some differences due to pesticide exposure: the total number of adults was lower in colonies that had high pesticide concentrations, and the average weight of a newly-emerged bee was lower in colonies that had a low pesticide concentrations. No affects were observed in Mississippi, however, and the biggest differences were between sites, rather than between treatment groups. Colonies in Mississippi probably had many more sources of forage, and even at the same site in Arizona, colonies in a year with higher rainfall did much better than colonies in the year with lower rainfall, even though plenty of water was always available to drink. The CO2 concentrations were higher in colonies given high pesticide concentrations. We also found that the pesticide was very stable in honey over many months, so once in stored honey it is not likely to degrade.
Technical Abstract: The effects of agricultural pesticide exposure upon honey bee colonies is of increasing interest to beekeepers and researchers, and the impact of neonicotinoid pesticides in particular has come under intense scrutiny. To explore potential colony-level effects of a neonicotinoid pesticide at field-relevant concentrations, honey bee colonies were fed 5- and 20-ppb concentrations of clothianidin in sugar syrup while control colonies were fed unadulterated syrup. Two experiments were conducted in successive years at the same site in southern Arizona, and one in the high rainfall environment of Mississippi. Across all three experiments, adult bee masses were about 21% lower among colonies fed 20-ppb clothianidin than the untreated control group, but no effects of treatment on broodproduction were observed. Average daily hive weight losses per day in the 5-ppb clothianidin colonies were about 39% lower post-treatment than in the 20-ppb clothianidin colonies, indicating lower consumption and/or better foraging, but the dry weights of newly-emerged adult bees were on average 6–7% lower in the 5-ppb group compared to the other groups, suggesting a nutritional problem in the 5-ppb group. Internal hive CO2 concentration was higher on average in colonies fed 20-ppb clothianidin,which could have resulted from greater CO2 production and/or reduced ventilating activity. Hive temperature average and daily variability were not affected by clothianidin exposure but did differ significantly among trials. Clothianidin was found to be, like imidacloprid, highly stable in honey in the hive environment over several months.