Dispersibility of the Pale Grass Blue Butterfly m (Lepidoptera: Lycaenidae) Revealed by One-Individual Tracking in the Field: Quantitative Comparisons between Subspecies and between Sexes.

The pale grass blue butterfly (Lepidoptera: Lycaenidae) has been used as an environmental indicator species for radioactive pollution after the Fukushima nuclear accident. Here, based on the one-individual tracking method in the field, we examined dispersal-associated and other behavioral traits of this butterfly, focusing on two subspecies, in mainland Japan and in Okinawa. The accumulated distances in the adult lifespan were 18.9 km and 38.2 km in mainland and Okinawa males, respectively, and 15.0 km and 7.8 km in mainland and Okinawa females, respectively. However, the mean distance from the starting point was only 24.2 m and 21.1 m in the mainland and Okinawa males, respectively, and 13.7 m and 7.4 m in the mainland and Okinawa females, respectively. Some quantitative differences in resting and feeding were found between subspecies and between sexes. The ARIMA (autoregressive integrated moving average) model indicated that the dispersal distance was 52.3 m (99% confidence interval value of 706.6 m) from the starting point in mainland males. These results support the idea that despite some behavioral differences, both subspecies of this butterfly are suitable as an environmental indicator because of the small dispersal ranges.