Taxonomic revision of charon-, floridanum- and muscaeforme-groups of Gryon Haliday, 1833 (Hymenoptera, Scelionidae) from Japan, with descriptions of two new species and host information

Japanese species of the muscaeforme-group, charon-group, and floridanum-group of Gryon have been revised. Among the species of the muscaeforme-group, G. fulvicoxa sp. nov. is newly described. Gryon misha Kozlov & Kononova, syn. nov. is considered a junior synonym of G. japonicum (Ashmead). Gryon maruzzae Mineo, syn. nov. and G. sugonjaevi Kozlov & Kononova, syn. nov. are considered junior synonyms of G. yamagishii Mineo. Among the species of the charon-group, G. shisa sp. nov. is newly described. Gryon hakonense (Ashmead) syn. nov. is considered as a junior synonym of G. philippinense (Ashmead). Among the species of the floridanum-group, G. pennsylvanicum (Ashmead) is recognized. Host records of the three species groups are also revised.


Introduction
Gryon Haliday, 1833 is one of the largest genera in Scelioninae with 332 species known in the world (Johnson 2019). Almost all of them are egg parasitoids of Heteroptera, mainly Pentatomidae, Reduviidae, and Coreidae (Masner 1983). In Japan, 23 species are known (Ashmead 1904;Mineo 1979;1980a, b, 1981, b, 1991Kozlov and Kononova 1989;Yasuda 1990; Kononova and Fursov 2005;Kononova and Kozlov 2008) and four of them are recorded as natural enemies of pests of rice, soybeans, vegetables and fruits (Appendix 1). Some members of Scelionidae, including Gryon, are important natural enemies of agricultural pests. The life history of G. japonicum was partially provided by Noda (1993), however, life cycles of other species are almost unknown. Owing to the potential of Gryon as biocontrol agents, some biological and ecological studies have also been conducted (Noda 1993;Arakawa 2004, 2005;Nakajima and Fujisaki 2010;Nakajima et al. 2012).
Variation. This species has a correlation between the size of specimens and the convexity of the frons: in small specimens the frons is more convex than in large specimens. This correlation is also known in G. pennsylvanicum (Ashmead, 1893) (Masner 1983 (Thunberg, 1783), and L. chinensis. Noda (1990b) reported that G. japonicum also emerged from sentinel eggs of C. schmidti (Kritshenko, 1916)       Remarks.  provided photographs of the holotype of G. japonicum. Based on these photographs, morphological characters of specimens examined in this study are the same as the holotype. Gryon orestes (Dodd, 1913) is recorded from Japan as G. flavipes (Ashmead, 1905) in Mineo (1979) and G. nixoni (Masner, 1965) in Mineo (1981). We examined the voucher specimen determinated by Mineo, and found that the specimen is a small individual of G. japonicum. We also examined the holotype of G. mischa held at ZIN, and confirmed that it is also G. japonicum. Mineo, 1981 Figs 1C, 2C, 3C, 4C, 5C, I, 6C
Variation. The sculpture of frons and postgena of the small specimens is weaker than that of the large specimens. In the smallest specimens collected in Kôchi University, the sculpture of the frons is reticulate-granulate with puncture and the sculpture of postgena is barely costate. In contrast, the sculpture of the frons in the larger specimens is clearly reticulate, and that of the postgena is also clear. The number of sulci is large in large specimens. The pronotal cervical sulcus is weakly foveolate in the large specimens, however, the foveolae are lacking in small specimens. Owing the smaller host egg size, specimens that emerge from A. soridius are smaller and the sculpture is weaker than those that emerge from the larger eggs of H. unipunctatus.
Biology. Females of G. philippinense are found in the "Komomaki", rice straw belts wrapped around trees during winter. Some females are also found on the underside of leaves of evergreen broad-leaved trees. In spring, females can be collected from blossoms of Acer palmatum Thunberg (Sapindaceae

Remarks.
Among the charon-group species, G. philippinense differs from other species in the sculpture of the median sulcus of the postgenal bridge (Fig. 4D).  provided some pictures of holotypes of G. philippinense and G. hakonense. Also, we examined the voucher specimen of Mineo (1979) deposited in ELKU. Based on these pictures and the voucher specimens, G. hakonense is a junior synonym of G. philippinense. Watanabe (1951) redescribed G. hakonense based on specimens that emerged from eggs of Homoeocerus marginiventris and Riptortus pedestris. We could not, however, find the voucher specimens in SEHU and the redescription is insufficient to identify the species properly, therefore, we excluded the two host records. Description. Female. Length = 1.6-1.7 mm. Color. (Figs 1E, 2E). Body mainly black. Mandibles brown. A1-6 and legs (excluding coxae) yellow.
Key to species of Japanese muscaeforme-group of Gryon Sculpture of frontal depression (Fig. 3A, B) irregular. Angular point of occipital carina (Fig. 4A, B) Mineo (1981) established the muscaeforme-group based on the body sculpturing, the form and sculpturing of the frontal depression and mesosoma, and the form of the carinae on the occiput. Kononova and Kozlov (2008) provided another concept for the muscaeforme-group based on the presence of the hyperoccipital carina. As a result of our study, however, some members of muscaeforme-group sensu Kozlov and Kononova (G. misha (synonymized with G. japonicum), G. japonicum, and G. yamagishii) do not have the hyperoccipital carina. Species group concepts by Mineo are based on multiple well-defined characters, therefore, at least for the Palearctic species, the concept by Mineo is more practical.

Discussion
While the hosts of some species are known, the life history of most Scelionidae in the field is unknown. Some specimens examined in this study were collected in winter. They were collected from under the bark of Zelkova serrata (Fig. 12), in the "Komomaki" (see above), and the underside of leaves of evergreen broad-leaved trees. Also, sometimes they showed overwintering aggregation with other species of Scelionidae such as Trissolcus corai , T. cultratus (Mayr, 1879, T. gonopsidis (Watanabe, 1951), T. japonicus (Ashmead, 1904), T. plautiae (Watanabe, 1954), Idris sp., Psilanteris sp., and Telenomus sp. Therefore, natural cracks such as narrow slit under the bark or artificially created cracks such as "Komomaki" and corrugated fiberboards could provide suitable winter habitat for not only predators (Fye 1985;Togashi et al. 1988;Yoshimura et al. 1995;Korenko and Pekár 2010; Band Trap research group of Abiko Bird Museum 2012) but also parasitoids. In spring, some females collected from maple blossoms. Nectar of small blossoms could work as one of important energy sources for adults in this season. Further investigation on their life cycles is required to understand and enhance their functions as natural enemies. Dr S. Kamitani (ELKU) for providing useful information about X. reticulatum in Japan, and to Dr E. Talamas (Florida State Collection of Arthropods, Gainesville, Florida, USA) for providing clear images of G. pennsylvanicum. This study was partly supported by a doctoral scholarship of Kyushu University and KAKENHI (JP17J07148 for YK; JP26850032 and JP19H00942 for TM) from the Japan Society of the Promotion of Science.