Insects have the capacity to accumulate electric charge. For bees, charging up facilitates passive electrostatic interactions with flowers as well as aerial electroreception. Placodes are a prominent class of antennal olfactory sensilla in bees that were noted by Erickson for their putative electrostatic properties which could enhance olfactory sensitivity (Erickson Jr, 1982). Yet, to date, this hypothesis has not been empirically investigated. Herein, conducting multidisciplinary research, I investigate two hypotheses: placodes play a role in olfaction, owing to electrostatics and additionally I propose that placodes may constitute a new candidate electroreceptor in bees. Using 3D SBFSEM reconstruction, I examine the morphology and ultrastructure of placodes in Bombus terrestris, provide new anatomical insights, and show that in Apis mellifera drones, placodes undergo a distinct morphological change post-mortem that is also associated with a change in their electrostatic profile. In freshly removed A. mellifera drone antennae, the local electric field potential not only differs between the placode and surrounding cuticle but also within the placode itself. Local negative electric field potentials are typically recorded on the olfactory pore-rich regions of the placodes. To investigate the charging mechanism in placodes, I conduct elemental analysis of bee antennae. Exploring antennal function with electrophysiological techniques, the antennae of B. terrestris, were not found to respond to electric field stimuli alone. However, an increase in antennal responses to paired olfactory and electric field stimuli were recorded compared to the same olfactory stimulus alone. Computational models incorporating empirical data indicate that both the placode geometry and charge distribution could enhance odour capture in a fluid flow. Taken together, my results provide new insights into sensory placodes, the potential role of microscale heterogeneities in charge distribution and their olfactory role in bees. The role of placodes in electroreception remains elusive, yet warrants further investigation.
Investigating the structural and electrostatic properties of antennal placode sensilla in bees and their functional significance for olfaction and electroreception
Harris, B. H. (Author). 17 Jun 2025
Student thesis: Doctoral Thesis › Doctor of Philosophy (PhD)