Undertaker honeybees, a special group of workers in Apis cerana species, remove dead bees through “undertaking behaviour” triggered by a signal associated with death. However, the mechanism behind how the undertakers instantly recognize dead honeybees remains unclear.
In a study published in Entomologia Generalis, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) investigated the signals used by undertakers to detect death in honeybees.
They compared the body temperature and volatiles of living and dead bees using semi-volatile sampling, gas chromatography (GC), and coupled GC-mass spectrometry, and analyzed the effect of body temperature on the evaporated cuticular hydrocarbons (CHC emissions, CHEs) using thermal imaging and simulation.
Honeybees have a complex social system and rely on the cooperation of their hive mates to survive. When a honeybee dies, it’s important for the other bees to recognize the loss and remove the body to prevent disease and maintain hive hygiene.
Specific cuticular hydrocarbons
Undertakers in honey bees use specific cuticular hydrocarbons (CHCs) to recognize dead bees, according to a study conducted by researchers from the Xishuangbanna Tropical Botanical Garden.
To recognize dead mates, honeybees use a combination of visual and olfactory cues. Bees have excellent eyesight and are able to detect the presence of dead or injured bees within the hive. They also have a keen sense of smell and can detect the scent of a dead bee, which is different from the scent of a healthy bee.
When a honeybee dies, it releases a pheromone called oleic acid, which signals to other bees that it is dead. This pheromone spreads quickly throughout the hive and alerts other bees to the presence of the dead bee.
Once a dead bee is identified, worker bees will remove the body from the hive and dispose of it outside.
Effect of body temperature
The researchers compared the body temperature and volatiles of living and dead bees using semi-volatile sampling and gas chromatography, and then analyzed the effect of body temperature on cuticular hydrocarbon emissions using thermal imaging and simulation.
They also tested the antennal perception of bees toward specific CHCs and other honey bee pheromones using inhibition and release bioassays.
The study found that the reduced CHEs caused by the lowered body temperature of dead bees are the major chemical difference between live and dead bees, and that body heat-induced CHE is the life signal of active bees and inhibits undertaking behavior.
The removal of body parts is related to the cuticle area, and other tactile or non-volatile cues showed no inhibition.
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