Collection localities for the adult butterfly samples. (a) A map of Japan. Minor collection localities for control samples are shown together with the Fukushima Dai-ichi Nuclear Power Plant (FNPP) in red. Distances from the FNPP are indicated by circles. (b) A map of the Tohoku and Kanto districts. The seven major localities from which the adult samples were collected are shown by black dots. Takahagi and Kita-Ibaraki are treated as a single locality, “Takahagi”, in this study because of their proximity. Minor localities are shown by open circles. The FNPP is shown in red. Distances from the FNPP are indicated by circles.