Sexual communication by pheromones in a firefly, Phosphaenus hemipterus (Coleoptera: Lampyridae)

Fireflies are the classic example of organisms that use light signalling for sexual communication. However, many genera have diurnally active adults for which the use of light signals for courtship seems unlikely. It is generally accepted that diurnal fireflies use pheromones instead of light signalling for sexual communication, even though robust observational data or convincing experimental evidence is lacking. In several field experiments, we investigated whether sexual communication in the diurnal P. hemipterus is based upon pheromones rather than on light emission. During the daytime, males were attracted to females without the aid of visual cues. Males coming from the downwind side of females arrived first. Arrival directions of males to females were strongly nonrandom and were correlated with downwind direction, i.e. possibly into the direction from which a pheromone plume is dispersed. Males arrived more rapidly when the wind came from a fixed direction and wind speed was high. Although the presumed pheromone signal still attracted males at a distance of 20 m, its maximal sampling range was at a relatively close range (ca. 43 m after 3 h). More males were attracted when females showed signalling behaviour. These results strongly suggest that sexual communication in P. hemipterus is based entirely on pheromones.