These experiments were conducted to explore the differences among different bee stock in terms of colony-level behavior, as reflected in colony size, hive weight changes, and within-hive temperature and CO2 concentrations. The bee stocks included Pol-line and Russian bees (both stocks are resistant to Varroa mites and developed by USDA) and an unselected Italian stock obtained from a commercial breeder. Two experiments were conducted.First experiment, 2021-22. In May 2021 eighteen bee colonies in painted, 10-frame, wooden Langstroth boxes (43.7 l capacity) were divided into three groups of six and each group was re-queened with one of three bee stocks: Russian, Pol-line or unselected Italian. Colonies were observed for eggs to ensure that the queens successfully established. The hives were placed on stainless steel electronic scales (Tekfa model B-2418 and Avery Weigh-Tronix model BSAO1824-200) (max. capacity: 100 kg, precision: ±20g; operating temperature: -30ºC to 70ºC) and linked to 16-bit dataloggers (Hobo UX120-006M External Channel datalogger, Onset Computer Corporation, Bourne, MA) with weight recorded every 5 minutes. All hives faced south. Temperature sensors (iButton Thermochron, resolution ±0.06°C, accuracy ±0.5°C , accessed using 1-Wire Drivers x64, version 4.05) enclosed in plastic cassettes (Thermo Fisher Scientific, Waltham, MA) were stapled to the center of the top bar on the middle frame in the bottom box and set to record every 5 min. CO2 probes (model GMP251, Vaisala Inc., Helsinki, Finland), calibrated for 0-20% concentrations, were placed on top of the center frames in the top box of each hive and linked to dataloggers set to record every 5 min.Hives were assessed on 15 June using a published protocol (see Meikle WG, Weiss M (2017) Monitoring colony-level effects of sublethal pesticide exposure on honey bees. Journal of Visualized Experiments (129) e56355. doi:10.3791/56355). Briefly, each hive was opened after the application of smoke, and each frame was lifted out sequentially, gently shaken to dislodge adult bees, photographed using a 16.3 megapixel digital camera (Canon Rebel SL1, Canon USA, Inc., Melville, NY), weighed on a portable scale (model EC15, OHaus Corp., Parsippany, NJ), and replaced in the hive. Frame photographs were analyzed later in the laboratory (see below). During the first assessment all hive components (i.e. lid, inner cover, box, bottom board, frames, entrance reducer, internal feeder) were also shaken free of bees and weighed to yield an initial mass of all hive components. Hives were assessed every 4 weeks thereafter until 3 Nov., after which hives were left undisturbed until the final evaluation 9 Feb. 2022.Second experiment, 2022-23. The experiment described above was repeated in 2022, except that the number of colonies per treatment group was increased to 10. The time period between hive evaluations was increased to 5-6 weeks. At each hive assessment, a sample of 100-150 adult bees was taken from within the brood nest of the colony.for genetic analysis at another laboratory.Adult bee masses are in kg adult beesBrood surface areas are in square cm.Hive weights are in kgTemperatures are in degrees CentrigradeCO2 concentrations are in parts per million. The sensors used were calibrated from 0 to 20% (or 200,000 ppm). At very low values, such as near ambient CO2 concentration (about 400 ppm) the reading may not be accurate, that is, it may show values less than the known ambient CO2 concentration. In general, caution should exercised when interpreting extreme values.