<b>The heat is on: impact of heat waves on critical thermal maxima in larvae and adults of solitary bee </b><b><i>Osmia bicornis</i></b><b> </b><b>(Hymenoptera: Megachilidae)</b>

Extreme temperature events, such as heat waves, are increasing in frequency, magnitude, and duration. These events are believed to contribute to pollinator decline. Critical thermal maxima (CT_max) is a key physiological trait for understanding an organism’s ecology and predicting their responses to changes in climate. In this study, we investigated whether different life stages with distinct thermoregulatory behaviors differ in their CT_max in the solitary bee <i>Osmia bicornis</i>, one of the most common and important pollinators in Central Europe. Additionally, we tested the influence of excessively high temperatures, heat waves, on the CT_max in <i>Osmia bicornis</i>. We found CT_max varied among life stages, with adults exhibiting higher CT_max than larvae. Both females and males of adult bees showed a negative correlation between CT_max and body mass. Interestingly, adult bees exposed to different heat waves during their larval stage did not exhibit significant shifts in CT_max. These results suggest that bees may have limited capacity to enhance heat tolerance in response to prior heat exposure.极端气温事件（如热浪）的发生频率、强度及持续时长均呈上升趋势。此类事件被认为是引发传粉者种群衰退的重要因素。临界热极限（Critical Thermal Maxima, CTmax）是阐释生物体生态学特性、预测其对气候变化响应的关键生理性状。本研究以中欧地区最常见且重要的传粉者之一——独居蜂两角壁蜂（Osmia bicornis）为研究对象，探究具有不同体温调节行为的不同生命阶段个体的CTmax是否存在差异。此外，本研究还探究了极端高温（即热浪）对两角壁蜂CTmax的影响。研究结果显示，不同生命阶段的个体CTmax存在差异，成虫的CTmax高于幼虫。成虫雌雄个体的CTmax均与体重呈负相关。有趣的是，幼虫期暴露于不同热浪环境的成虫，其CTmax并未出现显著变化。上述结果表明，这类蜂类在应对前期高温暴露时，提升热耐受能力的潜力有限。