Togashia horii ( Togashi, 1962 )

Valliappan, Subramanian, Megalaa, N, Annamalai, Indra, Vidhya, G, Subbiah, Gireesh K, Ranjith, K & Nagappan, Nagappan, 2024, Larva and Life History of Togashia horii (Hymenoptera, Tenthredinidae) Feeding on Cornus controversa (Cornaceae) in Honshu, Japan, Bulletin of the National Museum of Nature and Science. Series A, Zoology 50 (2), pp. 69-74 : 70-73

Togashia horii ( Togashi, 1962)

( Figs. 1 , 2 )

Taxonus horii Togashi, 1962: 203 ; Togashi, 1965: 251, pl. 126, 6; Togashi, 1976: 1; Seiyama and Tachikawa, 1983: 182; Murota and Kurokawa, 1985: 252; Tanaka et al., 1985: 189; Togashi, 1988: 88; Abe and Togashi, 1989: 556; Takakura, 1991: 21; Togashi, 1992: 38; Haneda et al., 1998: 320; Togashi, 1998: 262; Nakamura, 2003: 260; Nagase, 2004: 1252; Naito et al., 2004: 41.

Togashia horii : Wei, 1997: 135; Taeger et al., 2010: 305; Shinohara and Ibuki, 2016: 53; Nagase and Watanabe, 2018: 948; Yoshida, 2019; Naito, 2019: 57; Naito, 2020: 398, fig. 394.

[Undetermined sawfly larva]: Anonymous, 2008, 2020a, b.

Adult specimens examined. Hokkaido: 1 ♀ (fig. 394 in Naito, 2020), Kiyosato, Abashiri , 2. VII. 1998 , H. Hara. Niigata pref.: 1 ♀, Arupuno-sato, 900 m, Yuzawa-machi , 30. VII. 2006 , A. and N. Shinohara; 11 ♀ 4 ♂, Sasagamine, Myoko , 13. VII. 2018 , A. Shinohara; 3 ♀ 3 ♂, same data but 18. VII. 2018 ; 3 ♂, Sasagamine, Myoko , larvae coll., 31.VIII. 2022 , mat. 1. IX., em. 24. V. 2023, H. Kojima; 2 ♀ 11 ♂, same data but em. 25. V. 2023 ; 4 ♀ 5 ♂, same data but em. 30. V. 2023 ; 6 ♀ 4 ♂, same data but em. 3. VI. 2023 . Nagano pref.: 1 ♀, Hakuba-jiri, 1200 m, Hakuba-mura , 12. VII. 2007, T . Naito; 1 ♀, Mt. Kasadake, 1700 m, Yamanouchi-machi , 4. VII. 2023 , A. Shinohara.

Distribution. Japan: Hokkaido, Honshu, Shikoku, Kyushu. Collection records of this species are available from Hokkaido ( Naito, 2020), Tochigi prefecture ( Tanaka et al., 1985), Kanagawa prefecture ( Togashi, 1988; Nagase, 2004), Niigata prefecture ( Togashi, 1992), Nagano prefecture (present work), Ishikawa prefecture ( Togashi, 1962), Fukui prefecture ( Murota and Kurokawa, 1985; Togashi, 1992; Haneda et al., 1998), Hyogo prefecture ( Naito et al., 2004), Ehime prefecture ( Seiyama and Tachikawa, 1983) and Oita prefecture ( Takakura, 1991). On the internet, photographs of the characteristic larvae of T. horii are available from Yamagata prefecture ( Anonymous, 2008), Nagano prefecture ( Anonymous, 2020a) and Kumamoto prefecture ( Anonymous, 2020b). As shown above, we have examined adult specimens only from Hokkaido, Niigata prefecture and Nagano prefecture. As far as we are aware, T. horii has only been recorded from Japan.

Host plant. Cornaceae : Cornus controversa Hemsl. var. controversa .

Field observations and rearing records. On September 14, 2014, Shinohara encountered several groups of large gregarious sawfly larvae infesting the leaves of Cornus controversa ( Fig. 1A, B ) in Tsugaike at an altitude of about 1800 meters, Otari, Nagano prefecture. The feeding of those larvae apparently caused much damage to the Cornus trees in the area ( Fig. 1D ). No attempt was made to rear them. In mid-September, 2015, Shinohara also observed a larva of probably the same species trying to enter a dead branch (about 2 meters above the ground) of a tree at the same locality. This behavior of the mature larva suggested that the larva probably belonged to the subfamily Allantinae and was presumably Togashia horii because of its large size and the habitat having natural environmental conditions probably similar to those of the type locality. However, the larva was left undetermined due to lack of clear evidence.

On August 31, 2022, Kojima found two groups of gregarious larvae feeding on C. controversa in Sasagamine at an altitude of about 1300 meters, Myoko , Niigata prefecture. The larvae were brought into a rearing room in Nagano city, where the larvae of one group matured on September 1 and a total of 35 adults emerged from May 24 to June 3, 2023. The males tended to emerge earlier than the females, as shown above in the list of specimens examined. The larvae of another group matured and entered a dead branch of a tree on September 9 ( Fig. 1F ).

Three females that emerged on June 1 and 3, 2023, were put in a plastic container with twigs of C. controversa and they oviposited on June 2–3 and 12–13. The eggs deposited on June 12–13 ( Fig. 2B–E ) hatched on June 24–25 ( Fig. 2G–I ) but all the larvae died for unknown reasons by June 29.

Life history. According to our observations on the mountains in Nagano prefecture and Niigata prefecture, the rearing records and the adult collection records examined (see above), the adults were active in July and the larval feeding period was in August to September. In the rearing room in Nagano city, the adults emerged at the end of May to June. At least in the areas studied or in the areas with similar climatic conditions, this species apparently has only one generation a year.

Seiyama and Tachikawa (1983) mentioned l One female emerged on April 30, 1974 in rearing z (original in Japanese) in Komenono, Ehime prefecture. Unfortunately, no more data about the rearing, including the discovery date of the larvae, were published. Naito (2020) stated l Thought to be multivoltine, with adult emergence from spring to autumn z (original in Japanese) without showing evidence or references. Presumably, his statement was based on the published collection records of the adults in Hyogo prefecture, where the adults were collected in April, July and September according to Naito et al. (2004). Multivoltinism of this species in warmer regions should be confirmed by further studies.

Eggs and oviposition. The eggs are laid in long rows along the leaf veins ( Fig. 2B–E ; figures 2 and 3 in Togashi, 1976). Togashi (1976) noted that l The eggs are laid into the spongy mesophyll tissues of the leaf through the upper epidermis, making slits approximately 0.3 mm long along the leaf vein (Fig. 3A) z and l They hatch in about 10 days z. We have observed that the freshly deposited eggs were not conspicuous ( Fig. 2B, C ) but they became inflated and easily recognizable ( Fig. 2D, E ) after several days. In our rearing records, the egg period was 11–13 days.

Larvae. Early instar ( Fig. 2G–I ): head brown to black; trunk translucent creamy white. Late instar ( Fig. 1A–C ): head black covered with thin whitish wax powder layer; trunk dark yellow in ventral half (spiracles and below), black broad longitudinal line just above spiracles through supraspiracular and laterodorsal regions, and dorsal surface above these black lines gray with thick white wax layer; thoracic legs brownish. Just after molt, head orange and dorsal surface without wax layer ( Fig. 1C , left). Mature larva ( Fig. 1F ): similar to late feeding instar, but dorsal surface without white wax layer and slightly tinted with blue.

The late-instar larvae form a large group usually on the lower surface of a leaf, often occupying almost entire lower surface ( Fig. 1A ). The cast skins of the larvae are left on the margins near the base of a leaf and on the stem ( Fig. 1E ). The larvae often consume the Cornus leaves nearly completely, apart from the midrib ( Fig. 1D, E ). On maturity, the larvae go into dead branches or wood ( Fig. 1F ) and stay inside until emergence as adults.

Comparison with other sawfly larvae. The older larvae of this species are distinctive in their striking color pattern and large size, and all larval instars in their gregarious feeding behavior ( Figs. 1A–C , 2G, H ). The mature larvae enter dead branches or wood ( Fig. 1F ). These characteristics make T. horii larvae easily distinguishable from other sawfly larvae in Japan. The unidentified larvae shown on the internet ( Anonymous, 2008, 2020a, b) most probably belong to T. horii .

Two Japanese species of sawflies other than T. horii are known to be associated with Cornus , a Pamphiliidae , Pamphilius japonicus Shinohara, 1985 ( Shinohara et al., 2019) and a Tenthredinidae , Asiemphytus fasciatus Takeuchi, 1929 ( Shinohara and Ibuki, 2016). The larva of P. japonicus is a solitary leaf-roller readily recognized by its distinctive pamphiliid features ( Shinohara et al., 2019). Asiemphytus fasciatus belongs to the same subfamily Allantinae as T. horii . The larvae of the two species resemble each other in general morphology, and also the wood-burrowing behavior of mature larvae, but they differ greatly in coloration and feeding behavior. The late instar larvae of A. fasciatus have mainly creamy white to pale gray trunk with dorsolateral rows of black dots and they are solitary, not gregarious, feeders ( Shinohara and Ibuki, 2016).

Figures

Fig. 1. Togashia horii, late instar larvae (A–C), damage of host leaves (D), eaten leaf with larval exuviae (E) and mature larvae entering dead branch (F). A, B, D, E, Tsugaike, September 14, 2014; C, Sasagamine, August 31, 2022; F, Nagano, September 9, 2022. Photographed by Shinohara (A, B, D, E) and Kojima (C, F).

Fig. 2. Togashia horii, female adult (A), host leaf with eggs deposited inside (B–E) host leaf with larval exit holes (F) and early instar larvae (G–I). A, June 12; B, upper surface, arrows showing rows of eggs inside, June 14; C, same leaf, underside, June 14; D, same leaf, upper surface, showing inflated eggs inside, June 18; E, same leaf, underside, June 18; F–H, June 26; I, June 28. All photographed indoors in Nagano by Kojima in 2023.