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Bumble bees are key pollinators with some species reared in captivity at a commercial scale, but with significant evidence of population declines and with alarming predictions of substantial impacts under climate change scenarios. While studies on the thermal biology of temperate bumble bees are still limited, they are entirely absent from the tropics where the effects of climate change are expected to be greater. Herein, we test whether bees' thermal tolerance decreases with elevation and whether the stable optimal conditions used in laboratory‐reared colonies reduces their thermal tolerance. We assessed changes in the lower (CTMin) and upper (CTMax) critical thermal limits of four species at two elevations (2600 and 3600 m) in the Colombian Andes, examined the effect of body size, and evaluated the thermal tolerance of wild‐caught and laboratory‐reared individuals of Bombus pauloensis. We also compiled information on bumble bees' thermal limits and assessed potential predictors for broadscale patterns of variation. We found that CTMin decreased with increasing elevation, while CTMax was similar between elevations. CTMax was slightly higher (0.84°C) in laboratory‐reared than in wild‐caught bees while CTMin was similar, and CTMin decreased with increasing body size while CTMax did not. Latitude is a good predictor for CTMin while annual mean temperature, maximum and minimum temperatures of the warmest and coldest months are good predictors for both CTMin and CTMax. The stronger response in CTMin with increasing elevation, and similar CTMax, supports Brett's heat‐invariant hypothesis, which has been documented in other taxa. Andean bumble bees appear to be about as heat tolerant as those from temperate areas, suggesting that other aspects besides temperature (e.g., water balance) might be more determinant environmental factors for these species. Laboratory‐reared colonies are adequate surrogates for addressing questions on thermal tolerance and global warming impacts. [ABSTRACT FROM AUTHOR]

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Interest in assessing the critical thermal limits of bees is rapidly increasing, as these physiological traits are good predictors of bees' potential responses to extreme temperature changes, which is relevant in the context of global climate change. However, estimates of thermal limits may be influenced by several factors and published studies differ in experimental methods and conditions, such as the rate of temperature change (ramping rate) and feeding status, which might yield inaccurate predictions and limit comparisons across taxa and regions. Using Africanized honey bees as a model organism, we assessed the effect of ramping rate (0.25, 0.5, 0.75, 1.0 and 1.5 °C min−1) and length of starvation (recently fed vs. fasted for 6, 12, and 18 h) on foragers' lower (CT Min) and upper (CT Max) thermal limits, as well as the effect of cold stress on CT Max. In addition, we evaluated the two approaches currently used to assess CT Max with a water bath: floating or submerging the testing vials in the bath. We found that critical thermal limits were influenced by ramping rates but not by the other assessed experimental conditions. On average, at ramping rates faster than 0.5 °C min−1, bees displayed a CT Min 1.1–2.6 °C lower and a CT Max 5.3–6.9 °C higher than those of the slowest ramping rate. We discuss the implications of these results and provide suggestions for future thermal studies on bees. • Critical thermal limits are predictors of organisms' responses to climate change, and they may be influenced by experimental methods and conditions. • We assessed the effect of the rate of temperature change, length of starvation, and exposure to low temperatures on bees' critical thermal limits. • Critical thermal limits were influenced by ramping rates, but not by the other assessed experimental conditions. • Cold and heat tolerances increased in response to faster temperature ramping rates. [ABSTRACT FROM AUTHOR]