Size determines antennal sensitivity and behavioral threshold to odors in bumblebee workers

Area of Science:

• Entomology
• Animal Behavior
• Sensory Physiology

Background:

• Eusocial bumblebees (Bombus terrestris) display significant worker size variation.
• Size-related differences in workers correlate with task allocation (alloethism), with larger bees foraging and smaller bees performing nest duties.

Purpose of the Study:

• To investigate how worker size variation affects the peripheral olfactory system's morphology and physiology.
• To determine the impact of size on behavioral response thresholds to odors in bumblebee workers.

Main Methods:

• Morphological analysis of antennae, focusing on olfactory sensilla number and density.
• Electrophysiological recordings (electroantennogram) to measure antennal sensitivity to odors.
• Dual-choice behavioral experiments to assess odor detection thresholds and learning performance.

Main Results:

• Olfactory sensilla number and density on antennae significantly correlate with bumblebee worker size.
• Antennal sensitivity to odors increases with body size, with larger bees showing higher electroantennogram responses.
• Large workers responded to lower odor concentrations than small workers in behavioral tests; learning performance was similar.

Conclusions:

• Worker size variation in bumblebees directly influences olfactory sensilla number and thus individual odor sensitivity.
• Enhanced odor sensitivity in larger workers likely plays a role in the evolution of size-related division of labor within bumblebee colonies.