Circadian rhythm studies - temperature, CO2 and colony size data

In all files, temperature data are in degrees centigrade and CO2 data are in the original data in mA as generated by the CO2 sensors themselves. Colony weights are in kg.

For spreadsheet “Ag Commons Fall 2020 and Fall 2021” file, in October 2020 fifty bee colonies in painted, 10-frame, wooden Langstroth boxes with marked European queens and at least 2 frames of sealed brood, were identified. This experiment was originally part of a study on the use of cold storage in Varroa management (see Meikle et al. (2023) Cold storage as part of a Varroa management strategy: Effects on honey bee colony performance, mite levels and stress biomarkers. Scientific Reports 13:11842. doi: 10.1038/s41598-023-39095-5). Temperature sensors (iButton Thermochron) were placed in plastic cassettes and stapled to the center of the top bar on the middle frame in the bottom box and set to record every 30 min. in 2020 and every 15 min. in 2021. CO₂ probes (model GMP251, Vaisala Inc., Helsinki, Finland) were placed on top of the center frames in the top box of each hive and linked to HOBO UX120-006M dataloggers set to record every 5 min. On 1 October migratory entrance screens were placed on half of the colonies. Colonies were evaluated to estimate colony size (for a description of protocol see Meikle W.G., Weiss M. (2017) Monitoring colony-level effects of sublethal pesticide exposure on honey bees. J. Vis. Exp. 129, e56355. https://doi.org/10.3791/56355) and then placed in a cold storage unit (30 m³ internal volume, with CO2 and temperature monitors) set to 5°C with a dehumidifier and a roof-mounted exhaust fan operating 4 minutes per hour. Those hives remained in the completely darkened unit with the entrance covers until 22 October. The remaining hives were kept outside in the original apiary during that period. The experiment was repeated in October 2021.

For “Ag Commons Summer 2023” file, experimental protocol is as follows: In May 2023 16 bee colonies were obtained with marked queens of approximately the same size and in the same hives as described above. CO₂ probes and temperature sensors (HOBO Pendant Temp MX2201) were installed under the top bar of the middle frame in the bottom box and set to record every 5 min. Colonies were evaluated as described above on 15 June. On 22 June eight of the colonies were moved into the cold storage unit (30 m³ internal volume, with a dehumidifier and a roof-mounted exhaust fan operating 3 min per h, hereafter “CSU”) set to 5°C. Large mesh screens were placed over the entrance of each hive to provide space for the colony to dispose of dead bees but prevent bees from flying. After 6 d darkness, light cycles were turned on for 12 h from 6PM to 6AM each d for the remaining 12 d, after which colonies were moved back to their original apiary. On 11 July the brood frame photographs were taken but the adult bee mass was estimated visually as frames of bees. On 14 July the remaining eight colonies were moved into the CSU and subjected to the same treatment: 6 d darkness followed by 12 d of 12:12 light:dark cycle, with light from 6PM to 6AM. Those colonies were removed from the CSU to the outdoor apiary on 2 August and assessed on 3 August as described above for the first group of colonies. To estimate the adult bee mass for the post-CSU assessments, adult bee mass in kg was regressed on frames of bees using data from the pre-CSU evaluation, and the resulting equation used to convert frames of bees to adult bee mass.

For “Ag Commons Winter 2023” file, on 7 December 2023 eight bee colonies with marked queens were assessed by taking photographs of brood frames with a visual count of frames of bees (a full assessment was contra-indicated because of cold weather). CO₂ probes and temperature sensors (HOBO Pendant Temp MX2201) were installed under the top bar of the middle frame in the bottom box and set to record every 5 min. On 8 December the large mesh screens were placed over hive entrances and the hives placed in the cold storage unit (30 m³ internal volume, with a dehumidifier and a roof-mounted exhaust fan operating 4 min per h, hereafter “CSU”) set to 5°C. Colonies were initially subjected to 12 d of complete darkness. On 20 December a 12:12 light:dark cycle was initiated, with light from 6PM to 6AM, and continued until the end of the cold storage period. All colonies were removed on 25 January 2024, placed in their original locations in the apiary. Colonies were evaluated on 26 January. To estimate the adult bee mass for the pre-CSU assessments, adult bee mass in kg was regressed on frames of bees using data from the post-CSU evaluation, and the resulting equation used to convert frames of bees to adult bee mass.