Geographic differences in flash intervals and pre-mating isolation between populations of the Genji firefly, Luciola cruciata

1. Two types of Genji firefly, Luciola cruciata, have been recognised on the basis of the inter-flash interval. 2. The fast-flash and slow-flash type fireflies, distributed in the western and eastern parts of Japan, exhibit a 2- and 4-s interval of bioluminescence flash, respectively. In addition, an intermediate-flash type is found on the boundary between these two regions. 3. The differences in the responses of the males of four field populations to different intervals of artificial flashes were examined. 4. The results revealed that in the Aomori and Sendai populations (slow-flash type), a significantly larger number of males approached the 4- and 5-s flash intervals than approached the 2- and 3-s intervals of artificial flashes. On the other hand, in the Ohtsu population (fast-flash type), a significantly larger number of males approached the 2- and 3-s flash intervals than the 4- and 5-s intervals of artificial flashes. The Inuyama population (intermediate-flash type) did not show any particular preferences to flash intervals. 5. This study shows that in firefly populations, geographic variation in flash pattern can cause some degree of pre-mating isolation between populations.