In response to global warming, the distribution ranges of numerous insect species have been reported to have expanded to higher latitudes and/or elevations throughout the world. In this study, rearing experiments of the cycad blue butterfly, Luthrodes pandava, which has undergone range expansion around the Japanese archipelago, were performed by simulating the temperature and photoperiod conditions of three sites at different latitudes around Japan.
Using winter AMeDAS data for temperature conditions in Ishigaki City, Makurazaki City, and Kushimoto Town (Shionomisaki) from 2006 to 2015, the potential for overwintering in this species was tested. The results showed that 54-93% of individuals emerged as adults under conditions prevalent in Ishigaki. However, none of the larvae pupated and all died under conditions prevalent in Makurazaki and Shionomisaki. The findings show that this species can overwinter to the south of Okinawa, but not on the mainland north of Kyushu.
Increased summer temperatures were also simulated, and individuals were reared under three conditions. Using AMeDAS data for August (summer) in Sakai City, central Japan from 2006 to 2015, the development of this species was examined under the original data (average conditions), original+2°C, and original+4°C. The results showed that more than 90% of individuals emerged as adults under all conditions.
From the results of this study, if winter temperatures increase due to global warming, the northern distribution limit of overwintering populations of this species is expected to expand northward, the flying season will be extended, and populations will increase.
