Study reveals how honeybees recognize dead mates

A special group of workers in honey bees (Apis cerana), the undertakers, perform "undertaking behavior" to remove dead bodies. The undertakers rely on a signal associated with death to perform this behavior. However, it remains unclear how undertakers instantly recognize dead honey bees.

In a study published in Entomologia Generalis, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences have investigated the signals used by undertakers to detect death in honey bees.

The researchers compared the body temperature and volatiles of living and dead bees using semi-volatile sampling, gas chromatography (GC), and coupled GC-mass spectrometry. They then analyzed the effect of body temperature on the evaporated cuticular hydrocarbons (CHC emissions, CHEs) using thermal imaging and simulation.

They also tested the antennal perception of bees toward specific cuticular hydrocarbons (CHCs) using GC-electroantennographic detection. With synthetic CHCs and other honey bee pheromones, they performed inhibition and release bioassays.

According to the researchers, the removal of body parts is related to the cuticle area and not specific to the gland; the instantaneous life/death signal of honey bees is cuticular in origin; the major chemical difference between live and dead bees is the reduced CHEs in dead bees.

In addition, temperature and vapor pressure analyses indicated that the reduced CHEs were caused by the lowered body temperature of dead bees. Bioassays with heating apparatus, CHC regulation, and cross pheromone addition confirmed that body heat-induced CHE is the life signal of active bees and inhibits undertaking behavior.

Heated but CHC-reduced bees (by solvent washing or long heating evaporation) were removed, indicating that body heat alone cannot be a life signal. Heated dead bees coated with different amounts of wax were removed at different speeds depending on the wax quantity, suggesting that the removal was dose-dependent, and bees with lower CHEs were removed faster. Other tactile or non-volatile cues, which were always included in controls, showed no inhibition.

"This study confirms the CHEs as a life signal for sensitive and straightforward death recognition used by undertakers," said Wen Ping, first author of the study.