Ametastegia polygoni Takeuchi, 1929

Ryoo, Seung-Woo, Min, Jin-Young, Son, Seok-Yoon, Choi, Baek-Yong, Choi, Juho & Min, Kyoung-Bok, 2022, Taxonomic Notes and New Distribution and Host Plant Records for Sawflies and Woodwasps (Hymenoptera, Symphyta) of Japan VII, Bulletin of the National Museum of Nature and Science. Series A, Zoology 48 (4), pp. 193-213 : 197-198

Ametastegia polygoni Takeuchi, 1929

Japanese name: Itadori-kuro-habachi

( Fig. 3 )

Material examined. Honshu: Ibaraki Pref.: 3 $, Amabiki-kannon , Sakuragawa, coll. larvae on Fallopia japonica var. japonica , 5. V. 2022, mat. 12. V., em. 25. V. 2022, A. Shinohara .

Host plant. Polygonaceae : Fallopia japonica (Houtt.) Ronse Decr. var. japonica ( Takeuchi, 1929) .

Life history. On 5 May, 2022, a group of probably middle instar larvae were found on the underside of a leaf of the host plant in Sakuragawa , Ibaraki Prefecture. The larvae fed on the underside of the leaf, making large holes but usually leaving the thin upper surface tissue ( Fig. 3A–C ). In middle of May , several larvae matured and went into cork ( Fig. 3E ), not in soil. After about two weeks, three female adults emerged. This species has two or more generations a year ( Okutani et al., 1959) .

Remarks. As clearly indicated by the species epithet, the host plant of this species was already known when the species was described in 1929. Okutani (1954) gave a key to the larvae of four sawfly species feeding on Polygonum cuspidatum (= Fallopia japonica var. japonica ), including A. polygoni . Okutani et al. (1959) described the larva with good line drawings and gave notes on the life history. Here we give the photographs of the larvae for the first time.

Okutani et al. (1959) noted that A. polygoni has two or more generations a year and the larvae occur in May to July. The published collection records of the adults (Shinohara, 2000, 2001, 2005, 2014; Naito et al., 2004), mostly in April to June and none in mid-summer to autumn, and Shinohara`s observation recorded above, agree well with Okutani et al.`s statement. Naito (2020) mentioned without giving references or support- ing data that this species was multivoltine with adult emergence from spring to autumn.

Figures

Fig. 3. Ametastegia polygoni: A, Leaf of Fallopia japonica var. japonica, infested with larvae of A. polygoni, under side, 5. V. 2022; B, same leaf, upper side; C, same leaf, under side, with a group of middle or late instar larvae; D, late instar larva, 13. V. 2022; E, mature larvae entering cork, 13. V. 2022. A–C, Sakuragawa; D, E, Tsukuba (indoors). Photographed by Shinohara.