In Korean peninsula, twenty three species of Acronicta have been reported. Since the seven Acronicta species, A. carbonaria, A. cuspis, A. digna, A. intermedia, A. rumicis, A. strigosa and A. subornata, were firstly documented by Leech (1889), he (1900) added two species, A. major and A. tridens. After a few years, three species, A. leucocuspis, A. lutea and A. raphael, were recorded by Herz (1904). In the following studies, four species, A. bellula, A. alni, A. catocaloida and A. hercules were subsequently recorded (Seitz, 1938;Bryk, 1948;Pak, 1959). In the late 20th century, remaining seven acronictine species, A. adaucta, A. jozana, A. concerpta, A. vulpina, A. pruinosa, A. pulverosa and A. sugii were recorded by several researchers (Ahn et al., 1994;Ronkay et Park, 1993;Kononenko et al., 1998).

The Acronicta is the type genus of the subfamily Acronictinae, which is included in the family Noctuidae. Approximately 150 species have been reported within the Acronicta (Kononenko and Han, 2008). Acronictine species are widely distributed across the Palearctic, Oriental, Australian, and Nearctic regions. In particular, acronictine species are well adapted to the cool temperate forest of the Holarctic region (Kononenko and Han, 2008). The distribution is mainly concentrated in the Nearctic region with 90 described species, and the eastern Palearctic region with 56 described species (Kononenko and Han, 2008;Kishida, 2011;Han and Kononenko, 2010).

The larva of the Acronicta, which are known to be pests of forests, primarily consume woody shrubs and trees including fruit trees and street trees. For example, Acronicta intermeida infest Malmus domestica (apple trees), and Acronicta adaucta damages prunus species (Kishida, 2011). It is also worth noting that A. rumicis is indicated as an agricultural pest that damages maize and vegetable crops (Bereś, 2009;Szwejda, 2022).

The aim of the study is to report a newly recorded species, Acronicta gigasa to Korean fauna. This study also provided illustrations of adult and genitalia of the species with distributional data.

Materials and Methods

Specimen collection and preparation

All specimens were collected for this study using a light trap (mercury vapor lamp, 220V/400W) from dusk to midnight. The moths were euthanized using a 30% ammonia solution and then preserved in a freezer. The specimens were subjected to a 30 minute softening process at 50°C with high humidity within a sealed container. Subsequently, the wings were spread and dried for a period of four weeks at a temperature of 50°C in a drying oven.

Dissection and identification

The abdominal dissections were conducted in accordance with a modified version of the technique originally published by Robinson (1976), utilizing the EZ4 stereomicroscope (Leica Microsystems, Germany). The specimens and dissected genitalia were observed using a Canon EOS 6D camera with a Canon Macro Lens EF 100 mm, mounted on a Stack Shot Macro Package and dome illuminator Leica LED 5000 HDI, or a Tucsen Dhyana 400 DC digital camera with Leica S8AP0 stereomicroscope with the same dome illuminator. Photographs were taken and merged using Helicon Focus software (version 8.2.2. Pro, Helicon Soft, Ukraine) or Mosaic software (version 2.4) with Adobe Photoshop 2022 (version 23.5.1, Adobe, USA). Further detailed images of the genitalia were captured utilizing a Leica Z16 APO stereomicroscope (Leica Microsystems, Germany) with Optview software (Korea Lab Tech, Republic of Korea).

Results

Taxonomic accounts

Family Noctuidae Latreille, 1809

Noctuidae Latreille, 1809: 191. Type genus. Noctua Linnaeus

Subfamily Acronictinae Harris, 1841

Acronictinae Harris, 1841: 459. Type genus. Acronicta Ochenheimer

Genus AcronictaOchenheimer, 1816

AcronictaOchenheimer, 1816: 62, Type species. Phalaena leporina Linnaeus

Acronicta gigasaChang, 1991 (Fig. 1B, 1D, 1F, 1H, 2B, 2D, 2F) 큰뿔무늬저녁나방(신칭)

Acronicta gigasaChang, 1991: 313. Type locality. Taiwan

Material examined. Three males, Korea, Gangwon-do, Hongcheon-gun, Sinbong-ro, 343 (37°42' N 127°58' E), Altitude: 297 m, 6 VII 2023 (H. Han.), gen. slide no. IPE12106- 12108/ Jinsung Park; six males, Korea, Gangwon-do, Uljingun, Maehwa-myeon, Gilgok-ri, San 56-1 (36°47'N 129°20'E), Altitude: 304 m, 27 VII 2023 (H. Han., D. K. Ra.), gen. slide no. IPE12109, IPE12123-12127/ Jinsung Park; 1 female: Korea, Gyeonggi-do, Namyangju-si, Gwangneung (GPS unprovided), 29 VI 2001 (J. G. Lee.), gen. slide no. IPE12087/ Jinsung Park.

Diagnosis. This species, Acronicta gigasa, shares similar superficial morphological features with Acronicta major. Both species have grey-colored forewings and exhibit distinct black basal and tonal streaks. Not only the forewings but also the hindwings, labial palpi, antennae, colorations, and position of streaks are almost identical. However, Chang, who reported this species, only mentioned that it can be clearly identified by its genitalic morphology (Chang, 1991). Therefore, the detailed diagnosis is as follows. Regarding the wing pattern, only the basal streak tends to be less expressed on A. gigasa, and the reniform stigma is somewhat more distinct than in A. major. However, these features vary. So, genital dissection is necessary for accurate identification. A. gigasa differs from A. major in features of the genitalic capsule; A. gigasa has a more rounded end of valva; the posterior margin of the sacculus is more rounded; the length of the harpe is relatively longer than in A. major. The most conspicuous difference between A. major and A. gigasa is the aedeagus; A. gigasa has no distal diverticulum and a cluster of cornuti on the ventral diverticulum. In female genitalia, the length of ductus bursae is slightly shorter than A. major. The appendix bursae of A. gigasa are smaller than A. major, and appendix bursae are constricted medially in A. major. Near the entrance to the appendix-corpus bursae complex, A. gigasa has an inflated and membranous ductus bursae structure. In contrast, A. major has a relatively distinct, complex, and additive ductus bursae structure.

Description. Adult (Fig. 1B). wing span 50.0-55.0 mm. Head grey. Antenna filiform; scape ivory ventrally, dark brown dorsally, slightly thicker than flagellum; flagellum about one fourth of base ivory dorsally, rest of dorsal surface brown, dark brown ventrally. First segment of labial palpus ivory ventrally, black dorsally, slightly shorter than second segment, cylindrical; second segment of labial palpus ivory with black band on outer surface, cylindrical, approximately same length of compound eye; third segment ivory, black scales scattered, extremely thinner than second segment, cylindrical with blunt apex. Thorax and abdomen grey. Ground color of forewing grey; outer margin slightly curved inward at end of Cu₁ venation; black short line present following costa; basal black streak distinct or less expressed, branched following antemedial line; antemedial line black, faint, connected with basal dagger-shape streak; orbicular stigmata black, circular to oval, or diffused; reniform stigmata black, distinct with blackish suffusion from medial line, rarely diffused; postmedial line black, crenulated, significantly curved inward to wing base on Cu₁ venation; tornal streak black, straight, formed dagger-shape with postmedial line; terminal line black, dot-like on each cells. Ground color of hindwing ivory; discal spot brown, diffused; postmedial line black scales scattered, angeld on Cu₁ venation; terminal band black; Cilia ivory, tinged with dark brown on outer margin.

Male genitalia (Fig. 1D, 1F, 2B, 2D, 2F). Uncus stout, apically tipped, setose, curved at distal one third; two third from base narrower. Scaphium heavily sclerotized, thin, bifurcated distally. Subscaphium sclerotized basally, slightly sclerotized distally. Tegumen broad, marginally sclerotized. Juxta stout; groove present mesially; posterior margin obovate; anterior margin subrectangular, convex at middle in triangular shape. Vinculum thin, heavily sclerotized with two thin arms; two arms connected to base of sacculus. Saccus stout. Sacculus trapezoidal, robust. Harpe thin, strongly sclertotized, slightly shorter than half length of tegumen-vinculum complex. Valva marginally sclerotized, lobular, setose, rounded distally; one third from base slightly narrower. Aedeagus stout with heavily sclerotized carina; coecum broad; dorsal diverticulum broad, sack like; cluster of cornuti heavily sclerotized, dentate, dense; basal cornuti longer than distal cornuti near ductus ejaculatorius.

Female genitalia (Fig. 1H). Papillae analis setose. Posterior and anterior apophysis thin, sharp, approximately same length. Ostium vursae membraneous, funnel-shape. Ductus bursae membraneous, longitudinally rugose, almost one third length of corpus-appendix complex; sac-like ductus near entrance to appendix bursae present, membraneous. Appendix bursae membraneous, sac-like, semi-globular, connected to ductus seminalis. Corpus bursae membraneous, sac-like.

Distribution. Korea (this study), China (Sichuan, Hubei, Heilongjiang, Taiwan) (Chang, 1991).

Discussion

Through this study, we have organized morphological description and global distribution of Acronicta gigasa. In particular, we have provided detailed diagnosis and genitalic description that were not included in the original report of Acronicta gigasa (Chang, 1991). Acronicta major, which is highly similar to Acronicta gigasa in external morphology and causes misidentification, is known as a polyphagous forest pest. This species damages a wide range of tree species, including genera Acer, Prunus, and Malus of Rosaceae and Fabaceae. It is recognized as an agricultural and urban pest because these trees are commonly planted as fruit trees and street trees. We anticipate that the utilization of this study as fundamental data will be crucial for the exact identification of these two species and the development of effective pest management and control strategies.