Dichocrocis frenatalis Lederer, 1863

Matsui, Yuki, Wachi, Nakatada & Yoshiyasu, Yutaka, 2025, Discovery of Dichocrocis frenatalis Lederer, 1863 (Lepidoptera, Crambidae, Spilomelinae) in mangrove environments of the Ryukyu Islands, Japan, and tribal placement of the genus, ZooKeys 1243, pp. 143-158 : 143-158

Dichocrocis frenatalis Lederer, 1863

Figs 1 , 2 , 3 , 4 , 5 , 6 , 7 (Japanese name: nettai-kurosuji-ki-nomeiga )

Dichocrocis frenatalis Lederer, 1863: 448, pl. 17 fig. 15; Moore 1877: 616; Mally et al. 2019: electronic supplement file 1; Rao and Sivaperuman 2020: 20; Whitaker et al. 2023: 54.

Dichocrocis pandamalis (part): Hampson 1896: 306.

Diagnosis.

This species is externally similar to Conogethes pandamalis but can be distinguished by the continuous postmedial line straight from costa to CuA 2 in the forewing (in C. pandamalis it is interrupted and protruded between M 2 and CuA 2), and the narrow and black terminal line in both wings (in C. pandamalis the terminal line is lacking). Several undescribed species that are possibly congeneric have been found in Borneo [cf. Dichocrocis sp. 1 –9 of Whitaker et al. (2023)] and on the Andaman Islands (B. Sumit Kumar Rao pers. comm.), but D. frenatalis can be distinguished from these species based on the aforementioned characters. Dichocrocis sp. 15 and 16 of Whitaker et al. (2023) most resemble D. frenatalis , but they are best distinguished by broad terminal lines on both wings (in D. frenatalis they are very narrow).

Redescription.

Head (Fig. 1 A ). Frons yellowish orange, smooth. Vertex with yellow scales, anterior scales porrect, posterior scales erect. Maxillary palpus pale yellow, minute. Labial palpus yellow, upturned, first and second palpomeres with raised scales ventrally. Ocellus distinct, brownish, touching compound eye. Chaetosemata absent. Antennae about 4 / 5 of forewing length, light brown, dorsally covered with pale yellow scales, ciliate in male, filiform in female; scape yellow. Proboscis covered with yellow scales basally.

Thorax and legs. Thorax yellowish orange dorsally, pale yellow ventrally. Legs almost pale yellow; foreleg tibia with a bold blackish brown band medially; midleg tibia with a pair of spurs, inner spur about 2 / 3 length of outer one; hindleg tibia with two pairs of spurs, respective inner spurs about 2 times longer than outer ones.

Wings (Fig. 1 B – D ). Forewing length 6.00– 8.80 mm (Suppl. material 1: table S 1). The mean forewing length (± SD) was 7.10 ± 0.85 mm for males (n = 10) and 7.09 ± 0.71 mm for females (n = 10), with no statistically significant difference between sexes (t = – 0.029, df = 17.387, p = 0.978). Forewing ground color yellowish orange; basal fleck black, ending around Cu vein; antemedial line black, gently excurved; postmedial line black, straight from costa to CuA 2 vein, incurved at a right angle on CuA 2 vein, then oblique toward dorsum; marginal line black and narrow, running along termen; discocellular lunule black, nearly V-shaped; cell with a small black dot inside the discocellular lunule, but often disappearing; cilia pale yellow, banded with brownish orange medially. Hindwing ground color yellowish orange; discocellular lunule a black bar, often connected with postmedial line; postmedial line black, straight from costa to distal CuP vein, strongly narrowed (often disappearing there) and incurved at an acute angle between veins CuA 2 and CuP veins, running toward discocellular lunule, then thicken again and extending to dorsum; marginal line as in that of forewing, disappearing around tornus; cilia concolorous with that of forewing. In males, both wings tend to be narrower and each line thicker than in the female. Both wings underneath pale yellowish orange with the same maculation as above, but slightly weaker.

Wing venation (Fig. 2 ). Forewing Sc and R 1 separate; R 2 concurrent with R 3 + R 4 basally; R 3 stalked with R 4 at 1 / 4 distance from cell; R 5, M 1, M 2, M 3, CuA 1, and CuA 2 separate, almost equidistant; A 1 + 2 weakly sinuate near tornus; A 3 weak, straight; discal cell closed; male retinacular hook absent. Hind wing Sc + R 1 stalked with Rs at 4 / 5 of length; M 1 stalked with Sc + R 1 at upper angle of cell; M 2, M 3, and CuA 1 close basally; CuA 2 distant from CuA 1; CuP and A 1 + 2 strong; A 3 strong, weakly sinuate; female with two frenular bristles.

Abdomen. Yellowish orange; in male, terminal segment enlarged, hair-pencils often visible (Fig. 3 A ). Tympanal organs (Fig. 3 B, C ) with praecinctorium not bilobed; tympanum and conjunctivum forming a shallow angle medially; bulla tympani relatively small and narrow, anterior margin truncate; fornix tympani protruded ventrally; saccus tympani extending about 1 / 3 of 2 nd sternite, with straight posterior ridge; venula secundae absent. Male 8 th tergite (Fig. 3 C ) with a broad longitudinal sclerotization, its anterior end Y-shape, lateral margins tapered posteriorly, posterior end with strong wrinkles; both sides of posterior portion with a short linear sclerotization. Male 8 th sternite with two longitudinal sclerotizations, connected to strongly sclerotized and anteriorly convex anterior margin (Fig. 3 C ).

Male genitalia (Figs 4 , 5 ). Tuba analis (ta) weakly sclerotized, about 2.5 times longer than uncus. Uncus narrow, curved ventrad, apex covered with ventrally directed and bifid chaetae. Tegumen somewhat broad, tapered toward uncus. Parateguminal sclerite [sensu Solis et al. (2020)] extending from tegumen complicated in structure, composed of a saddle-shaped pad (sp) dorsally and a larger triangular sclerite (ts) ventrally, each with hair-pencils consisting of six types of specialized scales: the entire sclerite with many tufts of slender spatulate scales (ss), the dorsal and ventral tufts strongly bent inwardly, otherwise bent in various directions; the saddle-shaped pad dorsally with a tuft of somewhat broad spatulate scales (bs) that ventrally bent and distally tapered; the triangular sclerite with a tuft of long, lamellate scales (ls) at its apex, and a cluster consisting of short, blackish brown filiform scales (fs 1), longer and brown filiform scales (fs 2), and short hock-shaped scales (hs) internally. Gnathos absent. Saccus (sa) large and broad in dorsoventral view, rounded. Valva costa with a straight sclerotized ridge (sr) extending distal 1 / 4 and a large rounded basal bulge (bb), costal margin strongly concave at the termination of the ridge, dorsally with dense hair-like setae; inner surface with a wavy furrow (wf) running from apex to basal 2 / 3; ventral margin subtriangularly bulged medially, its apex with a tuft of long hair-like setae (vs); fibula (fb) spatula-shaped, basally separates into two arms, ventral arm concurrent with saccular base; sacculus (sl) a membranous band. Transtilla narrow, weakly connected medially. Juxta (jx) elongate, medially constricted with two longitudinal ridges, dorsal margin truncate, ventral margin medially concave and laterally connected to basal sacculus. Phallus (ph) with antero-ventrally extended caecum; vesica covered with fine microspines, without cornuti.

Female genitalia (Fig. 6 ). Papillae anales broad. Anterior apophyses slightly curved, apex blunt. Posterior apophyses broader than anterior ones, dilated near base. Antrum somewhat narrow, membranous, funnel-shaped. Ductus bursae membranous, sclerotized near corpus bursae, lateral margins of the sclerotization lightly tapered (Fig. 6 C ). Ductus seminalis emerging from the posterior end of ductus bursae. Spermathecal gland with lagena. Corpus bursae ellipsoid, 1 / 5 from anterior end with a transverse band composed of needle-like spines (ca 0.15–0.30 mm, Fig. 6 D ), and anterior portion from it sparsely covered with similar but shorter spines (ca 0.07–0.09 mm, Fig. 6 D ).

Material examined (n = 212 individuals).

Okinawa I. • 2 ♂; Nago-shi, Ôura ; 1 July 2009; U. Jinbo; NSMT . Ishigaki I. • 1 ♀; Takeda-rindô ; 21 May 2009; U. Jinbo; NSMT; • 1 ♂; Yarabe-rindô ; 22 Aug. 2022; I. Aoki; gen. slide no. YM 878; ELKU . Iriomote I. • 1 ♀; Tedô-san parking ; 30 May 2015; Y. Matsui; LT; ELKU; • 1 ex.; ditto; 5 Apr. 2024; T. Mano; LT; ELKU; • 1 ♂; Sonai ; 11 Jan. 2023; Y. Yoshiyasu; OMU; • 1 ♂ 1 ♀; ditto; 4 June 2024; T. Mano; • 2 ♀; Haemi ; 22 to 24 Nov. 2019; F. Ishiwata; gen. slide no. YM 876, 877; ELKU; • 3 ♀; ditto; 6 Oct. 2024; T. Mano; • 4 ♂ 5 ♀; Komi ; 25 May 2009; U. Jinbo; NSMT; • 1 ♂; Funaura ; 22 Sep. 2000; M. Kinjo & S. Katada; RUMF; • 1 ♀; ditto; 4 Oct. 2000; M. Kinjo & S. Katada; RUMF; • 1 ♂; ditto; 18 Jan. 2001; M. Kinjo & S. Katada; RUMF; • 1 ♀; ditto; 25 May 2009; U. Jinbo; NSMT; • 3 ♂ 2 ♀; ditto; 4 Apr. 2023; N. Wachi; TBRC and ELKU; • 5 ♂ 3 ♀; ditto; 21 Apr. 2023; N. Wachi; TBRC and ELKU; • 2 ♂; ditto; 24 Apr. 2023; N. Wachi; TBRC; • 4 ♀; ditto; 2 May 2023; N. Wachi; TBRC; • 3 ♀; ditto; 5 May 2023; N. Wachi; TBRC; • 5 ♂ 2 ♀; ditto; 20 May 2023; N. Wachi; TBRC; • 7 ♂ 1 ♀; ditto; 23 May 2023; N. Wachi; TBRC and ELKU; • 4 ♂ 1 ♀; ditto; 3 June 2023; N. Wachi; TBRC; • 5 ♂ 2 ♀; ditto; 6 June 2023; N. Wachi; TBRC and ELKU; • 4 ♀; ditto; 26 June 2023; N. Wachi; TBRC; • 4 ♂ 6 ♀; ditto; 4 July 2023; N. Wachi; TBRC; • 2 ♂ 2 ♀; ditto; 7 July 2023; N. Wachi; TBRC; • 2 ♂ 4 ♀; ditto; 12 July 2023; N. Wachi; TBRC; • 4 ♂ 4 ♀; ditto; 14 July 2023; N. Wachi; TBRC; • 1 ♂ 1 ♀; ditto; 13 Mar 2024; N. Wachi; TBRC; • 1 ex.; ditto; 4 Jun 2024; N. Wachi; prey of Maira aenea (Fabricius) ( Diptera : Asilidae ); iNaturalist observation ID: 220722951; TBRC; • 1 ex.; ditto; 18 Jun 2024; N. Wachi; prey of M. aenea ; iNaturalist observation ID: 224300521; TBRC; • 2 ♂; ditto; 26 Mar 2025; N. Wachi; TBRC; • 4 ♂ 3 ♀; ditto; 9 Apr 2025; N. Wachi; TBRC; • 1 ♀; ditto; 3 Dec. 2024; Y. Matsui & N. Wachi; ELKU; • other 90 individuals; ditto; N. Wachi; TBRC (see Suppl. material 2: table S 2).

Distribution.

India ( Nicobar Islands) ( Lederer 1863), Indonesia (Sumatra Island) ( Mally et al. 2019), Hong Kong ( Whitaker et al. 2023), Japan (Okinawa, Ishigaki, and Iriomote Islands) (this study).

Biological notes.

Our collection data suggest that the adults occur almost year-round. In the mangrove environment of Funaura, Iriomote Island, aggregations of adults on the underside of leaves were occasionally observed during the day (Fig. 7 A, B ). The aggregations included both sexes, although males were significantly more numerous. Some adults were observed being preyed upon by a robber fly, Maira aenea (Fabricius) ( Diptera , Asilidae ) (Fig. 7 C, D ). The occurrence of this robber fly in mangrove environments has been reported in previous studies ( Utsugi 2006; Tomazovic and Grootaert 2010).

Tribal placement.

The results from our molecular phylogenetic analysis placed D. frenatalis in Steniini (see below). In addition, the following genital characters, as proposed by Mally et al. (2019) for Steniini , support this placement: bifid uncus chaetae, undulated valva costa, well-separated valva fibula and distal sacculus, broad saccus, phallus with caecum, and corpus bursae with spinose texture and lacking signa. Since D. frenatalis is the type species of Dichocrocis , we assign the genus to the tribe Steniini .

Remarks.

In this study, we identified the Japanese specimens of this species as D. frenatalis based on the wing maculation of the type specimen (abdomen missing) preserved in the Natural History Museum, London, UK ( NHMUK) (Fig. 1 B ), in addition to the original description. We consider this identification to be justified at this time for the following reasons: 1) the abdomen of the type specimen is lost, rendering identification based on genitalia impossible, 2) no additional specimens of this species have been collected at the type locality (B. Sumit Kumar Rao pers. comm.), and 3) although Whitaker et al. (2023) illustrated many (putative) Dichocrocis species, none of them exhibit wing maculation matching that of D. frenatalis .

Figures

Figure 1. Dichocrocis frenatalis adults. A. Head; B. The holotype (bottom) preserved in NHMUK (photo by Richard Mally); C. Male; D. Female.

Figure 2. Dichocrocis frenatalis female wing venation.

Figure 3. Dichocrocis frenatalis abdominal structures. A. Male abdominal tip with visible hair-pencils (indicated by arrows); B. Tympanal organs; C. Male abdominal cuticle (slide no. YM 878). b. ty: bulla tympani, con: conjunctivum, f. ty: fornix tympani, hp: hair-pencils, prae: praecinctorium, sac. ty: saccus tympani, s 8: sternite 8, t 8: tergite 8.

Figure 4. Dichocrocis frenatalis male genitalia (slide no. YM 878). bb: basal bulge of valva costa, bs: broad spatulate scale, fb: fibula, fs 1: filiform scale 1, fs 2: filiform scale 2, hs: hook-shaped scale, jx: juxta, ph: phallus, sa: saccus, sl: sacculus, sr: sclerotized ridge of valva costa; ss: slender spatulate scale, ta: tuba analis, vs: valva setae, wf: wavy furrow.

Figure 5. Dichocrocis frenatalis male genitalia. A. Parateguminal sclerites (most scales removed, slide no. YM 1276); B. Whole genitalia, unmounted, left lateral view (internal hair-pencil scales removed); C. Whole genitalia, unmounted, dorsal view; D. Ditto, dorsal view; D. Ditto, ventral view. ls: lamellate scale 1, ph: phallus, sa: saccus, sp: saddle-shaped pad, ts: triangular sclerite, ss: slender spatulate scale, vs: valva setae.

Figure 6. Dichocrocis frenatalis female genitalia. A. Whole genitalia, ventral view, spermatophore in the corpus bursae indicated by dotted circle (illustration by YY); B. 8 th to 10 th abdominal segments, lateral view (spermathecal gland excluded); C. Sclerotization of ductus bursae, magnified view (slide no. YM 877); D. Spines on corpus bursae, magnified view (slide no. YM 877).

Figure 7. Biology of Dichocrocis frenatalis in Funaura, Iriomote Island, Japan. A. Aggregation of adults on the underside of a leaf (23 May 2023), a female is indicated by an arrow, while the others are males; B. Aggregation of male adults on the underside of a leaf (26 Aug. 2023); C. An adult preyed upon by a mangrove-associated robber fly, Maira aenea (Diptera: Asilidae) [18 June 2024, photo by Nakatada Wachi (@ wachinakatada); https://www.inaturalist.org/observations/224300521; accessed on 11 Mar. 2025] D. Pinned specimens of the robber fly and its moth prey in Fig. 7 C.