Allomorpha hirasana Takeuchi, 1929

Shinohara, Akihiko, Ibuki, Shin-ichi & Hara, Hideho, 2021, Life History and Larva of Allomorpha hirasana (Hymenoptera, Tenthredinidae) Feeding on Symplocos in Japan, Bulletin of the National Museum of Nature and Science. Series A, Zoology 47 (2), pp. 99-105 : 101-103

Allomorpha hirasana Takeuchi, 1929

( Figs. 1–3 )

Host plant. Symplocaceae : Symplocos sawafutagi Nagam. ( Okutani, 1967).

Field observations and rearing records. On June 10, 2019, one solitary larva ( Fig. 1B–D ) was found on the undersurface of a leaf of the host plant in Bato (N36°44′32.92″ E140°10′0.53″, 154 m), Nakagawa Town, Tochigi Prefecture. The larva was found on a leaf of a basal shoot of about 30 cm long on a stump near a stream in a rather dark deciduous forest with little sunshine. The larva had eaten the leaves from edge ( Fig. 1A ). It stopped feeding and moving on June 19, slightly shrank by June 21 ( Fig. 1E ) and cast skin ( Fig. 1F–G ) and entered the soil on June 22 .

A female adult emerged on April 25, 2020 ( Figs. 2 , 3A ). An earthen cell was found in the soil later ( Fig. 3B ). There was a cast skin of the prepupa in the cell ( Fig. 3B ). The female was kept in a container with a fresh branch of the host plant from April 25 to 29. Ovipositing behavior was not observed. On May 9, two very small larvae were found on the leaves used for the oviposition experiment ( Fig. 3E ). They were noticed because they had made small holes on the leaf by infestation ( Fig. 3E ). Because the consumed amount of the leaf was small and no cast skins were found, we regard the larvae as the first instar, which hatched probably on May 8. The two larvae were solitary, each found on a separate leaf, and each of the two leaves had a scar along the basal margin ( Fig. 3C–D ), which should be the exit of the larva from the egg inside of the leaf. One larva died on May 12. On May 17, the other larva molted (the first observed molt), thus becoming the second instar ( Fig. 3F ). On May 24, the larva molted, thus becoming the third instar ( Fig. 3G ). On May 26, the larva molted again, thus becoming the fourth instar ( Fig. 3H–J ), which was the last feeding stage. On June 5, the larva became a prepupa by casting the skin and went into the soil ( Fig. 3K ).

Larva. First instar ( Fig. 3E ): Head dark olive green. Trunk dull greenish white, cuticle opaque, without distinct white wax powder. Second instar ( Fig. 3F ): Head and trunk entirely dull greenish white, cuticle opaque, without distinct white wax powder. Third instar ( Fig. 3G ): Dull pale gray, wholly covered with white wax powder. Fourth instar ( Fig. 3I–J ): Length about 19 mm. Dull pale gray, wholly covered with white wax powder (no wax cover just after molt, Fig. 3H ). Mature larva (prepupa) ( Figs. 1F–G , 3K ): Length about 14 mm. Head light beige; trunk light greenish white, cuticle smooth and shiny, without white waxy coating.

Earthen cell ( Fig. 3B ). Without fiber and rather easily broken with fingers; inside wall rather smooth.

Summary of life history. The above observations suggest that the general life history of A. hirasana in Bato area is as follows. There is one generation a year. The adult emerges in late April and inserts an egg into the leaf tissue along the outer margin of the basal part of leaf, one egg per leaf. The egg period is 10–14 days. The larva is a solitary external feeder. The first instar lasts about nine days, the second instar about seven days, the third instar about two days and the fourth instar about ten days. The early instar larva makes holes on the leaf by feeding ( Fig. 3E ), while the late instar larva feeds on the leaf from margin. The fourth instar larva, when matured, casts skin (extra molt) and becomes a prepupa and immediately enters the soil, where it makes an earthen cell. There the prepupa hibernates and becomes a pupa by casting the prepupal skin next spring .

The above summary is mainly based on the observations on the male individual. The larva shown in Fig. 1 is a female and the larva in Fig. 3 is a male. The latter hatched from an unfertilized egg deposited by the former female. The last feeding instar and prepupa ( Figs. 1B–G , 3I–K ) show no conspicuous sexual differences, whereas the early and middle instar larvae and the definite number of molts (instars) is still unknown for the female.

Symplocos as a host plant of sawflies and its possible implications in generic classification. Larvae of sawflies utilize variety of plant groups as diets but, so far as we are aware, only two species of different genera of Tenthredinidae have been recorded as attached to Symplocos . One of them is A. hirasana ( Okutani, 1967; present work) and the other is Neocorymbas sinica Wei and Ouyang, 1997 , from Jiangxi, China ( Wei et al., 1997). Okutani (1967) listed Symplocos sawafutagi as a host plant of A. hirasana , as noted in the introduction, and Wei et al. (1997) simply noted lHost: Symplocos paniculata ( Symplocaceae )z for Neocorymbas sinica without giving an explanation. These are the only available references to Symplocos -feeding sawflies and the immature stages and life history of these species were totally unknown.

The genus Allomorpha belongs to the subfamily Allantinae and is represented by five species from China besides A. hirasana from Japan ( Taeger et al., 2010). For the five Chinese species, host plants are unknown. Shinohara and Ibuki (2016) pointed out the occasional existence of close one-to-one host plant relationships between tenthredinid sawfly species groups/genera and plant genera/families. Examples are the tenthredininine genus Conaspidia Konow, 1898 with Araliaceae (the sikkimensis group with Aralia and the scutellaris group with Kalopanax ) ( Shinohara and Ibuki, 2011) and the allantinine genus Emphytopsis Wei and Nie, 1998 with Stewartia ( Theaceae ) ( Shinohara et al., 2014). As discussed in the introduction, some authors ( Takeuchi, 1955; Okutani, 1967; Abe and Togashi, 1989; Togashi, 2000; Naito et al., 2004; Yoshida, 2006; Naito, 2019, 2020) treated Allomorpha as a synonym of Taxonus , whose representatives are associated with Rosaceae ( Okutani, 1967; Smith, 1979; Macek, 2010). The known exceptions are the Japanese species T. fluvicornis Matsumura, 1912 and T. montanus Togashi, 1992 , which are attached to Fallopia and Persicaria ( Polygonaceae ), respectively ( Okutani, 1959, 1967; Kato, 2018); the generic position of these two species may need revision. If the still unknown hosts of the five Chinese species of Allomorpha are Symplocos , it will be a strong support for the validity of the genus Allomorpha . The other Symplocos -associated genus, Neocorymbas , belongs to the subfamily Tenthredininae , and this host association probably evolved quite independently.

Figures

Fig. 1. Allomorpha hirasana, all photographed in Nakagawa, 2019. —A, Branch of Symplocos sawafutagi with leaves partly eaten by a larva of A. hirasana; B, female last feeding instar larva, June 11; C, same larva, June 15; D, same larva, June 16; E, same larva, shortly before molt, June 21; F, same larva, matured, just after molt, June 22; G, same larva and cast skin, June 22.

Fig. 2. Allomorpha hirasana, female adult. —A, Habitus, dorsal view; B, same, lateral view; C, same, ventral view; D, head, frontal view.

Fig. 3. Allomorpha hirasana, all photographed in Nakagawa, 2020. —A, Female adult, emerged on April 25 (same individual as in Fig. 2); B, earthen cell, half broken, with cast larval skin, April 26; C, basal part of leaf with remains of egg inside, an arrow showing exit of larva, May 10, upper surface; D, same, under surface; E, male first instar larva and three holes on a leaf made (eaten) by the larva, May 9; F, second instar larva, with cast larval skin (arrowed), May 17; G, third instar larva, May 25; H, fourth instar larva, just after third molt, with cast larval skin (arrowed), May 26; I, J, same larva, May 28; K, prepupa and cast larval skin (arrowed), June 5.