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Overwintering States of the Pale Grass Blue Butterfly Zizeeria maha (Lepidoptera: Lycaenidae) at the Time of the Fukushima Nuclear Accident in March 2011

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Overwintering States of the Pale Grass Blue Butterfly Zizeeria maha (Lepidoptera: Lycaenidae) at the Time of the Fukushima Nuclear Accident in March 2011

Ko Sakauchi et al. Insects.

Abstract

The Fukushima nuclear accident in March 2011 caused the massive release of anthropogenic radioactive materials from the Fukushima Dai-ichi Nuclear Power Plant to its surrounding environment. Its biological effects have been studied using the pale grass blue butterfly, Zizeeria maha (Lepidoptera: Lycaenidae), but the overwintering states of this butterfly remain elusive. Here, we conducted a series of field surveys in March 2018, March 2019, and April 2019 in Fukushima and its vicinity to clarify the overwintering states of this butterfly at the time of the Fukushima nuclear accident. We discovered overwintering individuals in situ associated with the host plant Oxalis corniculata under natural straw mulch as first-instar to fourth-instar larvae in March 2018 and 2019. No other developmental stages were found. The body length and width were reasonably correlated with the accumulated temperature. On the basis of a linear regression equation between body size and accumulated temperature, together with other data, we deduced that the pale grass blue butterfly occurred as fourth-instar larvae in Fukushima and its vicinity at the time of the accident. This study paves the way for subsequent dosimetric analyses that determine the radiation doses absorbed by the butterfly after the accident.

Keywords: Fukushima nuclear accident; Oxalis corniculata; Zizeeria maha; developmental stage; field survey; larval instar; life history; lycaenid butterfly; overwintering; pale grass blue butterfly.

Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Organisms of interest and field work localities. (a) An adult individual of the pale grass blue butterfly, Z. maha; (b) The host plant, the creeping wood sorrel, O. corniculata; (c) Field work localities. The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) is shown in red.
Figure 2
Figure 2
Habitats and the host plant O. corniculata in the field. Photographs taken in March are framed in green, and those taken in April are framed in yellow. The measuring tape (in f, h, and i) is in centimeters. (ad) Research sites. (a) Fukushima in March 2019; (b) Fukushima in April 2019 (the same site as a); (c) Kozaki in March 2019; (d) Kozaki in April 2019 (the same site as c). (e–l) O. corniculata. (e) Rifu in March 2019. Scale bar, 10 mm; (f) Rifu in April 2019; (g) Iwaki in March 2019. Scale bar, 10 mm; (h) Iwaki in April 2019. The host plants are deep under dried grass; (i) Fukushima in April 2019; (j) Fallen snow in Rifu in April 2019. Oxalis is indicated by red arrows; (k) Feeding marks (circled) in Fukushima in March 2018; (l) Feeding marks (circled) in Iwaki in April 2019.
Figure 3
Figure 3
Larvae, prepupa, and pupa in the field (circled). Photographs taken in March are framed in green, and those taken in April are framed in yellow. (af) Larvae. (a) Fukushima in March 2018; (b) Iwaki in March 2018; (c) Rifu in March 2019, inside dried and curled Oxalis leaves; (d) Tokai in March 2019; (e) Fukushima in April 2019; (f) Kozaki in April 2019 on Oxalis leaves; (g) A prepupa in Fukushima in April 2019. The left panel shows the natural positioning, and the right panel shows a prepupa on dried straw after being removed; (h) A pupa in Iwaki in April 2019 on dried straw.
Figure 4
Figure 4
Scatter plots showing the relationships between larval body size and the sum of the daily maximum temperature. Colors of dots indicate larval instars. (a) Scatter plot for longitudinal length (larval length). A linear regression line is shown; (b) Scatter plot for transverse width (larval width). A linear regression line is shown.
Figure 5
Figure 5
Timetables of developmental stages and larval instars in 2010–2011. Temporal changes in the daily maximum temperature are also shown above the timetables. The threshold temperature (14.0 °C) is indicated. The greatest emission date from the FDNPP (15 March 2011) is indicated by red arrowheads.

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