Abstract
Foraging bumblebees are electrically charged. Charge accumulation has been proposed to enable their ability to detect and react to electrical cues. One mechanism suggested for bumblebee electro-sensing is the interaction between external electric fields and electric charges accumulating on fine hairs on the cuticular body. Such hairs exhibit several functional adaptations, for example, thermal insulation, pollen capture and notably, the sensing of air motion such as flow currents or low frequency sound particle velocity. Both air motion and electric fields are ubiquitous in the sensory ecology of terrestrial arthropods, raising the question as to whether cuticular hairs respond to both stimuli. Here, a model-theoretical approach is taken to investigate the capacity of bumblebee filiform hairs as electric sensors and compare it to their response to air motion. We find that oscillating air motion and electric fields generate different mechanical responses, depending on stimulus frequency and body geometry. Further, hair morphology can enhance one sensing mode over the other; specifically, higher surface area favours electric sensitivity. Assuming a maximum stable charge on the hair that is limited only by electric breakdown of air, it is expected that an applied oscillating electric field strength of approximately 300 V m−1 produces comparable mechanical response on the hair as a 35 mm s−1 air flow oscillating at 130 Hz—an air disturbance signal similar to that produced by wingbeats of insects within a few bodylengths of the bumblebee. This analysis reveals that bumblebee filiform hairs can operate as bi-modal sensors, responding to both oscillating electric and air motion stimuli in the context of ecologically relevant scenarios.
Highlights
Bees typically possess a net positive electric charge [1,2,3]
The electric field associated with this charge exerts an electrostatic force on nearby charged or polarizable materials, for example, pollen
For honeybees and bumblebees respectively, the putative organs of electroreception are proposed to be the antennae and hairs, functioning as electro-mechanical transducers [7,8]. For both antennae and hairs, the presence of net charge was shown to increase the mechanical response generated by electric field stimuli
Summary
Bees typically possess a net positive electric charge [1,2,3]. The electric field associated with this charge exerts an electrostatic force on nearby charged or polarizable materials, for example, pollen. For honeybees and bumblebees respectively, the putative organs of electroreception are proposed to be the antennae and hairs, functioning as electro-mechanical transducers [7,8] For both antennae and hairs, the presence of net charge was shown to increase the mechanical response generated by electric field stimuli. Air motion torque on the hair is estimated using realistic stimulus signal parametrized from the ecologically relevant scenario of air disturbance from nearby insect wingbeats Taking this to be a perceivable stimulus, the electric field stimulus required to produce a similar hair response is calculated (§6). This theoretical approach offers a deeper understanding of hair-based electromechanical sensing and enables a fundamental generalizable modelling framework that will guide further research into electro-reception in air and its sensory ecological relevance
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