Death recognition by undertaker honey bees based on reduced cuticular hydrocarbon emissions

Removing dead conspecifics reduces pathogen transmission in social insects. Undertakers of the hive-bees can quickly detect and remove dead bees. The signals indicating instant death are unclear. In this study, we identified that undertaking was quickly elicited by the reduction in evaporated cuticular hydrocarbons (CHC emissions, CHEs). CHEs from dead bees were much lower than those from live bees, whereas heated dead bees with reproduced CHEs were not instantly removed. Physiological tests further showed that undertakers perceived and discriminated the major CHCs, and heated synthetic CHCs inhibited the undertaking behaviour. This study thus indicates that the reduced emissions of CHCs, particularly heptacosane and nonacosane, due to lower body temperatures in dead bees, are used by undertakers as a signal for detecting dead bees. Heptacosane and nonacosane emissions at hive temperatures are life signals. By changing the vapour pressure, then the ratio of emitted compounds, insect chemical communication can be fine-tuned by body temperature. The increasing frequency of extreme weather events may cause inaccurate death recognition, harming bee health.