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Agalope oshikirii n. sp., the first chalcosiine fossil (Lepidoptera, Zygaenidae) from Akita Prefecture, Japan

Published online by Cambridge University Press:  09 May 2025

Yui Takahashi Open the ORCID record for Yui Takahashi [Opens in a new window] ,
Hiroaki Aiba Open the ORCID record for Hiroaki Aiba [Opens in a new window]  and
Yositaka Sakamaki Open the ORCID record for Yositaka Sakamaki [Opens in a new window]
Yui Takahashi*
Affiliation:
Keio Yochisha Elementary School, 2-35-1, Ebisu, Shibuya, Tokyo 150-0013, Japan
Hiroaki Aiba
Affiliation:
Institute for Educational Practice Studies, 1-12-16, Kichijoji-kitamachi, Musashino, Tokyo 180-0001, Japan
Yositaka Sakamaki
Affiliation:
Faculty of Agriculture Kagoshima University, 1-21-24, Korimoto, Kagoshima 890-0065, Japan
*
Corresponding author: Yui Takahashi; y.takahashi.geol@yochisha.keio.ac.jp
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Abstract

Agalope oshikirii n. sp. (Zygaenidae, Chalcosiinae) is described from the uppermost Miocene–Pliocene Sanzugawa Formation in Akita Prefecture, northern Japan. Because we found a single fossil forewing in this study, we give a table of the forewing characters of various groups of the genus Agalope and related genera and compared them with this new species, confirming that it does not match any of the species. This is the first discovery of chalcosiine fossils in Japan and provides evidence of a historically broader distribution of the genus.

http://zoobank.org/999828b5-4f91-470f-bc15-6b6fe7a8ec61

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Journal of Paleontology , Volume 99 , Issue 1 , January 2025 , pp. 128 - 134
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Non-technical Summary

Agalope oshikirii n. sp. (Zygaenidae, Chalcosiinae) is described from the uppermost Miocene–Pliocene Sanzugawa Formation in Akita Prefecture, northern Japan. This is the first discovery of chalcosiine fossils and provides evidence of a historically broader distribution of the genus.

Introduction

The subfamily Chalcosiinae (Lepidoptera, Zygaenidae) is distinguished by its high morphological and ecological diversity. The group comprises ~70 genera and 370–400 species (e.g., Bryk, Reference Bryk and Strands1936; Tremewan, Reference Tremewan1973; Fletcher and Nye, Reference Fletcher, Nye and Nye1982; Yen et al., Reference Yen, Robinson and Quicke2005) and is distributed from Palaearctic eastern Asia, through subtropical southeastern Asia, to the Melanesian and Micronesian archipelagos (with the exception of the western Palaearctic genus Aglaope Latreille, Reference Latreille1809). To date, no fossil record of the subfamily has been identified (Sohn et al., Reference Sohn, Labandeira, Davis and Mitter2012) largely due to the lepidopterans’ low preservation potential, even in lacustrine deposits, as suggested by taphonomic simulations with existant species (Duncan, Reference Duncan1997).

The genus Agalope Walker, Reference Walker1854, consists of small to medium-sized chalcosiine moths known for their translucent and thinly-scaled broad wings with a colored forewing base and various blackish patterns on the forewing upperside. Adults are active from spring to late summer and are typically observed flying slowly during the day (Huang et al., Reference Huang, Zhu, Chen, Xu, Wang, Fan, Pan and Espeland2022). The genus currently includes 15 species, divided into four species groups—hyalina, eronioides, livida, and geoffi—distributed in the eastern Palaearctic and Oriental regions, including Kashmir, India, Nepal, Bhutan, northern Myanmar, various provinces in southwestern, central, and southern mainland China, Taiwan Island, and northern Vietnam (Huang et al., Reference Huang, Horie, Fan, Wang and Espeland2023).

Previously, six species groups—hyalina, eronioides, bieti, pica, glacialis, and immaculata—were recorded within Agalope (Yen et al., Reference Yen, Robinson and Quicke2005). Huang et al. (Reference Huang, Horie, Fan, Wang and Espeland2023) recently reviewed and modified the generic concept; they transferred the pica and glacialis species groups to a newly established genus Paragalope Huang and Horie in Huang et al., Reference Huang, Horie, Fan, Wang and Espeland2023 and the immaculata species group to another new genus, Rotundagalope Huang and Horie in Huang et al., Reference Huang, Horie, Fan, Wang and Espeland2023. Yen et al. (Reference Yen, Robinson and Quicke2005) highlighted that Agalope is not monophyletic, recommending the exclusion of Agalope glacialis (Moore, Reference Moore1872) and Agalope immaculata Leech, Reference Leech1898, supporting their transfer to other genera. Huang et al. (Reference Huang, Horie, Fan, Wang and Espeland2023) further excluded all species of the pica and bieti species groups (sensu Yen et al., Reference Yen, Robinson and Quicke2005) from Agalope, combining them with Agalope glacialis under a new genus based on similar genitalia structures. Thus, the concept of the genus Agalope is complex. Here, we report the first fossil specimen belonging to the genus Agalope (sensu Huang et al., Reference Huang, Horie, Fan, Wang and Espeland2023), which is also the first fossil representative within the subfamily Chalcosiinae.

Geological setting

The Sanzugawa caldera is located in the southern part of Akita Prefecture, northern Japan. It is filled by the Torageyama Formation, Sanzugawa Formation, and post-caldera volcanics (Takeno, Reference Takeno1988; Fig. 1.1, 1.2). The Torageyama Formation primarily consists of felsic pumice lapilli tuff formed by deisitic pyroclastic flows. The Sanzugawa Formation, made up of lake deposits, includes tuffaceous siltstone, mudstone, and sandstone with fossiliferous layers. The postcaldera Quaternary volcanics are distributed in the central part of the caldera (Takeno, Reference Takeno1988). Takeno (Reference Takeno1988), Ito et al. (Reference Ito, Utada and Okuyama1989), and Ito (Reference Ito2023) discussed the history of the Sanzugawa caldera. According to these studies, the first stage of a caldera-forming eruption occurred ~6–5 million years ago (Ma) at the Sanzugawa caldera, resulting in the deposition of the Torageyama Formation. Approximately 4–3 Ma, another major caldera-forming eruption happened in the eastern part of the Sanzugawa Caldera, leading to thick lacustrine sedimentation of the Sanzugawa Formation, with continuous deposition of the Torageyama Formation. The former is represented by lake deposits found in Minase-dam, Sanzugawa, and Oyasu areas in the southern part of Yuzawa. The formation mainly comprises alternating layers of tuffaceous sandstone and siltstone (Takeno, Reference Takeno1988). Well-preserved fossils, e.g., plants and insects, are found in the main part of the formation.

Figure 1.

Locality of the studied fossil. (1) Location of the Sanzugawa caldera in Tohoku region, northern Japan; based on Ito (Reference Ito2023). (2) Simplified geological map of the Sanzugawa caldera; based on Ito et al. (Reference Ito, Utada and Okuyama1989). (3) The location map based on the digital topographic map published by the Geospatial Information Authority of Japan (GSI).

The Sanzugawa Flora consists of 45 species and 30 genera, belonging to 20 families (Huzioka and Uemura, Reference Huzioka and Uemura1974). With seven species, Salicaceae is the largest family in the flora, followed by Betulaceae with five species, and Fagaceae and Sapindaceae with four species each. Prominent genera include Salix Linnaeus, Reference Linnaeus1753 with five species and Acer Linnaeus, Reference Linnaeus1753 with four species. Their probable habitats closely resemble the cool-temperate forest of northern Japan. Moreover, a majority of the Sanzugawa species are believed to have lived in forested valleys and on mixed slopes (Huzioka and Uemura, Reference Huzioka and Uemura1974), with the flora deposited in a freshwater lake basin. Oshikiri (Reference Oshikiri2001) also reported plant fossils, e.g., winged seeds of Oleaceae and Styrax protoobassia Tanai and Onoe, Reference Tanai and Onoe1961. Most Sanzugawa plants are identical or similar to late Miocene to earlier Pliocene species (Huzioka and Uemura, Reference Huzioka and Uemura1974).

Studies of insect fossils have been promoted by S. Oshikiri, a high school teacher, who described such species as Bibio sp. indet. (Bibionidae) and Tipulidae gen. indet. sp. indet., likely belonging to Ctenophorinae or Tipulinae (Oshikiri, Reference Oshikiri1979). Oshikiri (Reference Oshikiri1982) reported 27 specimens belonging to 14 families with brief descriptions, and seven different Aphididae types based on additional specimens (Oshikiri, Reference Oshikiri1988). Fujiyama (Reference Fujiyama1983) reviewed fossil localities in northern Japan, noting that Mycetophilidae and Bibionidae (Diptera), Ichneumonoidea and Formicidae (Hymenoptera), and Aphididae (Homoptera) are well represented among the insect fossils based on the occurrence list.

Material

The studied fossil is preserved in whitish tuffaceous siltstone and is part of Oshikiri’s insect fossil collection. It was derived from an outcrop of the uppermost Miocene–Pliocene Sanzugawa Formation beside the old Kurotakibashi Bridge (39°1’21”N, 140°35’12”E; Fig. 1.3), which was lost due to a landslide in 2008. The studied specimen is deposited in Geosta Yuzawa, Yuzawa City, Akita Prefecture with a repository number OF-I74. In describing the characters of the specimens below, we follow Efetov and Tarmann’s (Reference Efetov and Tarmann2017) terminology of Zygaenidae.

Repository and institutional abbreviation

Type specimen examined in this study is deposited in Geosta Yuzawa—Oshikiri Fossil Insect Collections (OF-I).

Systematic paleontology

Order Lepidoptera Linnaeus, Reference Linnaeus1758

Superfamily Zygaenoidea Latreille, Reference Latreille1809

Family Zygaenidae Latreille, Reference Latreille1809

Subfamily Chalcosiinae Hampson, Reference Hampson1893

Genus Agalope Walker, Reference Walker1854

Type species

Agalope basalis Walker, Reference Walker1854, by monotypy (currently a junior synonym of Chalcosia hyalina Kollar in Kollar and Redtenbacher, Reference Kollar, Redtenbacher and Hügel1844).

Agalope oshikirii new species

[Japanese name: Oshikiri-usuba-hotaruga]

Figure 2

Holotype

OF-I74, a separated forewing (Fig. 2.1), Geosta Yuzawa, Yuzawa City, Akita Prefecture, Japan.

Figure 2

Agalope oshikirii n. sp. (1) Holotype, OF-I74, a separated forewing. (2) Drawing of OF-I74. We follow the terminology of Zygaenidae by Efetov and Tarmann (Reference Efetov and Tarmann2017), with abbreviations for wing venation as follows: A = anal vein; CuA = cubital anterior; CuP = cubital posterior; M = median vein; R = radial vein; Sc = subcosta. (3) Color reconstruction of separated forewing of Agalope oshikirii n. sp. on the water surface in the lake. Art (2) and (3) are drawn by Kazuki Mera.

Diagnosis

Agalope oshikirii n. sp. is distinguished by the following combination of characteristics: medium-sized forewing (approximately 25 mm long) lacking blackish patterns; M2 and M3 veins are quite shortly stalked; R4, R5, M1, and M2 veins are parallel to each other; M3 vein is parallel to CuA1.

Occurrence

This species was discovered in the Sanzugawa Formation (latest Miocene–Pliocene) located in Sanzugawa Caldera, Yuzawa City, Akita Prefecture, Japan.

Description

Forewing 25.3 mm long, 12.2 mm wide, transparent, semitriangular. Forewing costa arched just before apex forming rounded wing tip. Termen almost straight, slightly concave between CuA1 and CuP. Deeper colored small patch occupying basal one-eighth of wing, bordered with thin black arcuate band. Discal and terminal blackish maculations absent. Wing venation including full complement of veins. Sc vein ending near two-thirds of costa. Cross veins between costa and Sc absent. Discal cell slender, 17.2 mm long, 3.7 mm wide, spanning two-thirds of wing length. Discal cell closed with rudimentary medial stem vein in its distal part. R1 and R2 separated and arising independently from anterior part of cell. R1 separated from Sc. R2 and R3–5 separated. R3 and R4 stalked. R3 + R4 shortly stalked with R5. R5 not strongly sinuate basally. Discocellular cross vein M1-M2 bent inward at medial stem. M1 anterior, M2 slightly posterior of medial stem vein in discal cell. M1 close to R veins at base. R4, R5, M1, and M2 almost parallel to each other. M2 and M3 quite shortly stalked. M2 not strongly curved anteriorly. M3 not strongly curved posteriorly, parallel to CuA1. CuA1 and CuA2 arising independently from discal cell. CuP distinctly present, complete. 1A+2A sinuate with basal fork. Cross vein between CuP and 1A+2A absent.

Etymology

The specific name is derived from Oshikiri S., a high school teacher who studied insect fossils from the Sazugawa Formation.

Remarks

The specimen is characterized by its semitriangular forewing, presence of a medial stem vein, a closed discal cell spanning two-thirds of wing length, and a complete CuP vein, as well as 1A+2A veins with a basal fork. These characteristics clearly indicate the association of this specimen with the subfamily Chalcosiinae.

The translucent broad forewing with a colored wing base in this specimen is consistent with the genus Agalope and closely related genera among members of the subfamily. Huang et al. (Reference Huang, Horie, Fan, Wang and Espeland2023) revised the concept of Agalope, diagnosed the genus by a forewing base bearing an orange patch extending from the costa to the base of cell 1A+2A, forewing veins M2 and M3 stalked, and the forewing bearing only one transverse band, which is sometimes vestigial or absent. The studied specimen shares these diagnostic characters of Agalope. It can be distinguished from members of the genera Rotundagalope and Agacysma Huang and Horie in Huang et al., Reference Huang, Horie, Fan, Wang and Espeland2023, because these genera have forewing veins M2 and M3 arising independently from the discal cell. Although the wing venations of Agalope and Paragalope are similar, they can be differentiated by the blackish bands on the forewing: Paragalope typically has two clear transverse bands extending from the base to the basal half of forewing or one thick, distinct black band occupying the basal third to half, whereas Agalope has only one narrow and blurry band present or lacks such black bands. Therefore, the specimen clearly belongs to the genus Agalope.

The genus Agalope is currently composed of four species groups: hyalina, eronioides, livida and geoffi (Huang et al., Reference Huang, Horie, Fan, Wang and Espeland2023). The studied specimen is different from the hyalina and geoffi species groups, which are characterized by relatively smaller forewings and the lack of a black band surrounding the basal patch. Although Agalope grandis Mell, Reference Mell1922, belonging to the hyalina species group has a medium-sized forewing, it also lacks basal black band. Additionally, members of the geoffi species group have a more rounded forewing termen. The new species is also distinct from the eronioides species group because species in this group have darker wings. The forewing of the livida species group, represented solely by Agalope livida Moore, Reference Moore1879a, is most similar in appearance to the studied specimen. The forewing of Agalope livida is medium-sized with an almost straight termen and lacks a dark transverse band on forewing. However, the wing venation of the specimen differs from Agalope livida due to the presence of a rudimentary medial stem vein. Additionally, the forewing veins R4, R5, M1, and M2 are parallel to each other, and M3 is parallel to CuA1. This vein configuration is distinctive within the genus. Therefore, the studied fossil is identified as Agalope oshikirii n. sp.

Discussion

Recent members of Agalope are distributed across a range that includes Kashmir, India, Nepal, Bhutan, northern Myanmar, and several provinces in southwestern, central, and southern mainland China, Taiwan Island, and northern Vietnam (Huang et al., Reference Huang, Horie, Fan, Wang and Espeland2023). The discovered fossil offers direct evidence of the presence of the species of Agalope related to the livida species group in the latest Miocene–Pliocene of Japan, suggesting a broader historical distribution for the genus.

Interestingly, the forewing of Agalope oshikirii n. sp. has characteristics more commonly found in other genera, e.g., Rotundagalope, Paragalope, and Agacysma, rather than most congeners of Agalope (Table 1). We compared the following ten character elements: (1) forewing length, (2) forewing width, (3) length-to-width (L/W) ratio, (4) discal cell length-to-forewing-length ratio, (5) presence of a colored patch in the base, (6) length from base to basal black band-to-forewing-length ratio, (7) presence of distinct maculations aside for base, (8) presence of paralleled R4, R5, M1, and M2 veins, (9) presence of quite shortly stalked M2 and M3 veins, and (10) presence of paralleled M3 and CuA1 veins. Agalope oshikii sp. n. is most similar to Agalope livida, sharing eight elements. It also shares six to eight elements with Rotundagalope immaculata (Leech, Reference Leech1898), Paragalope gracilis (Moore, Reference Moore1872), and Agacysma sinica Huang and Horie in Huang et al., Reference Huang, Horie, Fan, Wang and Espeland2023. In contrast, other species groups within Agalope—the hyalina species group (with two to five elements), the eronioides species groups (with four or six elements), and geoffi species group (with three or five elements)—display notable different from Agalope oshikirii n. sp. These distinctions offer insights into the evolution of Agalope and its related genera.

Table 1.

Correlations of Agalope oshikirii n. sp. and relatives using the following ten elements: (1) forewing length; (2) forewing width; (3) L/W ratio; (4) discal cell length/forewing length ratio; (5) presence of colored patch in base; (6) length from base to basal black band/forewing length ratio; (7) presence of distinct maculations except for base; (8) presence of paralleled R4, R5, M1, and M2; (9) presence of quite shortly stalked M2 and M3; (10) presence of parallel M3 and CuA1. Cells in red font are elements shared with Agalope oshikirii n. sp. Measurements in mm.

One hypothesis is that these Agalope-related genera were derived from the ancestral groups closely related to Agalope oshikirii n. sp. This hypothesis is supported by two main arguments. First, the overlapping of distributions of these genera suggests a broader historical range. Modern Agalope’s wide distribution implies that fossil congeners like Agalope oshikirii n. sp. could have extended farther into northern Japan. According to Huang et al. (Reference Huang, Horie, Fan, Wang and Espeland2023), Rotundagalope is endemic to mainland China (Sichuan and Gansu provinces). Agacysma is also endemic to mainland China (Shaanxi, Hubei Province, and Chongqing), and Paragalope has wider distribution in northeastern India, southwestern mainland China, Taiwan Island, Thailand, Vietnam, and the Greater Sunda Islands (Java). These wide distributions indicate that unknown Agalope groups could have branched out in various regions.

Second, shared wing venation characteristics between Agalope oshikirii n. sp. and these related genera indicate a common primitive origin. For instance, a length-to-width (L/W) ratio of ~2.0, a discal cell length-to-forewing-length ratio ~0.7, paralleled R4, R5, M1, and M2 veins, paralleled M3 and CuA1 veins, presence of basal patch with surrounding black band extending to the wing’s posterior margin could represent primitive features preserved in the fossil species Agalope oshikirii n. sp., with the long-stalked M2 and M3 veins being a derived trait. Therefore, it is plausible that unknown ancestral groups of Agalope related to Agalope oshikirii n. sp. branched into these Agalope-related genera. Primitive characteristics could be relatively well preserved in modern Agalope livida.

Acknowledgments

We express our gratitude to H. Takayanagi (Yuzawa Geopark Promotion Council) and H. Niiyama (Yuzawa City Board of Education) for providing a fossil material. We also thank A. Sasaki and S. Goi (Network of Earth Science Museums in Whole Akita Prefecture) for their reviews of regional geology. We are grateful to Keio Gijuku Academic Development Funds for financially supporting this study. Our thanks extend to R. Kukihara and T. Suguro (Keio Yochisha Elementary School) for their support of our research. Lastly, thanks to reviewers H. Rajaei and G.M. Tarmann, the manuscript was improved by their constructive comments.

Competing interests

The authors declare none.

Footnotes

Handling Editor: Torsten Wappler

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Figure 0

Figure 1. Locality of the studied fossil. (1) Location of the Sanzugawa caldera in Tohoku region, northern Japan; based on Ito (2023). (2) Simplified geological map of the Sanzugawa caldera; based on Ito et al. (1989). (3) The location map based on the digital topographic map published by the Geospatial Information Authority of Japan (GSI).

Figure 1

Figure 2 Agalope oshikirii n. sp. (1) Holotype, OF-I74, a separated forewing. (2) Drawing of OF-I74. We follow the terminology of Zygaenidae by Efetov and Tarmann (2017), with abbreviations for wing venation as follows: A = anal vein; CuA = cubital anterior; CuP = cubital posterior; M = median vein; R = radial vein; Sc = subcosta. (3) Color reconstruction of separated forewing of Agalope oshikirii n. sp. on the water surface in the lake. Art (2) and (3) are drawn by Kazuki Mera.

Figure 2

Table 1. Correlations of Agalope oshikirii n. sp. and relatives using the following ten elements: (1) forewing length; (2) forewing width; (3) L/W ratio; (4) discal cell length/forewing length ratio; (5) presence of colored patch in base; (6) length from base to basal black band/forewing length ratio; (7) presence of distinct maculations except for base; (8) presence of paralleled R4, R5, M1, and M2; (9) presence of quite shortly stalked M2 and M3; (10) presence of parallel M3 and CuA1. Cells in red font are elements shared with Agalope oshikirii n. sp. Measurements in mm.