Thermal limits of Africanized honey bees are influenced by temperature ramping rate but not by other experimental conditions

Authors: GONZALEZ, VICTOR - University Of Kansas; Oyen, Kennan; AVILA, OMAR - Cundinamarca Beekeepers Association Asoapicun; OSPINA, RODULFO - National University Of Colombia

Submitted to: Journal of Thermal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2022
Publication Date: 12/1/2022
Citation: Gonzalez, V.H., Oyen, K.J., Ospina, R. 2022. Thermal limits of Africanized honey bees are influenced by temperature ramping rate but not by other experimental conditions . Journal of Thermal Biology. 110. Article 103369. https://doi.org/10.1016/j.jtherbio.2022.103369.
DOI: https://doi.org/10.1016/j.jtherbio.2022.103369

Interpretive Summary: We measured how temperature tolerance of honey bees are impacted by experimental conditions such as ramping rates, starvation, and equipment type. Understanding how experimental conditions influences our estimates of physiological measurements is critical for unifying methodology amongst studies. Our study suggests that several factors may explain differences between thermal tolerance estimates in published research.

Technical Abstract: 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 (CTMin) and upper (CTMax) thermal limits, as well as the effect of cold stress on CTMax. In addition, we evaluated the two approaches currently used to assess CTMax 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 CTMin 1.1–2.6 °C lower and a CTMax 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.