All the better to smell you with: Sensilla diversity and sexual signaling in fireflies (Coleoptera: Lampyridae)

Fireflies are known to use one of two sexual signaling modes, bioluminescence or pheromones. Visual bioluminescent signals are detected by the firefly’s eyes while volatile pheromones are detected by the antennae. Previous research showed diversity of sensory organ size based on sexual signal mode, with bioluminescent fireflies having larger eyes and pheromone using fireflies having larger antennae, relative to body size (Stanger-Hall et al. 2018). Additionally, it was shown that males have larger sensory organs than their conspecific females (Stanger-Hall et al. 2018), suggesting that males actively searching for mates use these enlarged sensory organs to increase the probability of finding mates. Firefly antennae, like all other insects, are covered in morphologically and functionally diverse sensilla. While previous research has documented the antennal sensilla of one species of firefly, Luciola cruiciata (Iwaski et al. 1995), little is known about the diversity of firefly antennal sensilla, especially in respect to signal mode. It also remains unknown which sensilla are used for pheromone detection and how they are distributed across the firefly antenna. Here we document the antennal sensilla of 4 bioluminescent and 3 non-luminescent pheromone using species. We compare the morphological diversity between these species to identify differences between sexual signal modes. Finally, we identify potential pheromone-sensing sensilla by comparing the relative number of olfactory sensilla between bioluminescent firefly species and species that rely exclusively on pheromones for mate-search.