UC San Diego

The ability use vibrational signals to activate nestmate foraging is found in the highly social bees, stingless bees and honey bees, and has been hypothesized to exist in the closely related, primitively eusocial bumble bees. We provide the first strong and direct evidence that this is correct. Inside the nest, bumble bee foragers produce brief bursts of vibration (foraging activation pulses) at 594.5 Hz for 63±26 ms (velocityRMS=0.46±0.02mm/s, forceRMS=0.8±0.2 mN. Production of these vibrations significantly increased by 1.5 fold inside the nest when a forager successfully returned with artificial nectar (2.5 M sucrose solution) and the number of foragers exiting and entering the colony into a foraging arena significantly increased by 1.8 fold and 1.8 fold respectively as compared to when the colony was offered water. The nest is well suited to transmitting these vibrations, and the wax food pots and brood cells exhibit a transmission resonance at 300-700 Hz (1.9-2.3 fold increase in dB relative to other frequencies from 10 Hz to 10 kHz). Playbacks of foraging activation pulses at natural amplitudes (force=1mN, velocity=0.4 mm/s) results in a 1.2 fold increase in bees entering the foraging arenas as compared to playbacks of white noise adjusted to be equal in vibrational amplitude, force, and duty cycle to the natural signals. Thus, vibrational foraging activation signals may be a basal trait shared by primitively eusocial and highly social bees