Beyond the glow: proving the unity of pheromones and bioluminescent signals in glow-worm firefly courtship

Sexual communication in nocturnal fireflies has been presumed to be facilitated exclusively by bioluminescence, which has replaced the pheromones used by diurnal species. Although some fireflies are suspected of using combined signalling, this view has so far not been supported by empirical evidence, and these species have been viewed more as outliers. In this study, we have investigated the visual and olfactory capability of sexual communication of a night-active glow-worm firefly Lamprohiza splendidula (Linnaeus, 1767). We recorded and categorized the behaviour of searching males in reaction to four different experimental treatments, in which the females could be located based solely on visual or olfactory cues or a combination of the two. The pheromone-only treatment attracted significantly more males than the control, thus confirming pheromone utilization in sexual communication of this species. This work represents the first direct evidence of combined pheromone and bioluminescence use in fireflies and refutes the hypothesis of exclusive use of light in courtship of the nocturnal species. We theorize that this life strategy is likely to be inherent in the whole genus and possibly common in all glow-worm firefly species.