Flash Activity in Two Synchronic Firefly Species (Coleoptera: Lampyridae)

Synchronic flashing in fireflies is a precisely timed behavior. This is a potentially useful tool to study sensory processing, the location and circuitry of the flash oscillator, and neuroeffector processing and coupling. Synchronic flashing, once thought to occur only in Southeast Asian fireflies, has recently been shown to be a prominent part of the behavior of a North American Photinus and Photuris species. To gain insights into the mechanisms of synchronic timing in fireflies, we compared spontaneous flashing and entrainment flashing in Photuris frontalis LeConte, a synchronic firefly found in Georgia's Coastal Plain, to analogous flashing in Pteroptyx malaccae Olivier, a synchronic firefly found in Malaysia. The timing of spontaneously produced flashes and entrainment flashes was recorded by photometry. Artificially produced, rhythmic stimulus flashes were used to induce a counterfeit synchrony (between subject fireflies and an LED), i.e., flash entrainment. We found that the spontaneously produced interflash intervals were repeated with a high degree of precision in P. frontalis and P. malaccae. However, the pattern of flashing was different during spontaneous flashing and flash entrainment. An isolated P. frontalis flashed intermittently during spontaneously flashing and entrainment flashing. Flash entrainment in P. frontalis started with an initial inhibition and then steady-state entrainment occurred with a fixed delay. In contrast, an isolated P. malaccae flashed continuously during spontaneous flashing and entrainment flashing. No initial inhibition occurred at the start of entrainment, and there was a gradual change in interflash interval until steady-state entrainment occurred at a fixed delay. We think that in-depth studies of the flash activities of different synchronic firefly species, including the locally available P. frontalis, could help our understanding of rhythmic temporal coordination of behavior by the nervous system.