Epsteinius translucidus Lin, 2020

Lin, Yu-Chi, Braby, M. F. & Hsu, Yu-Feng, 2020, A new genus and species of slug caterpillar (Lepidoptera: Limacodidae) from Taiwan, Zootaxa 4809 (2), pp. 374-382 : 376-379

Epsteinius translucidus Lin , sp. nov.

( Figs 1–4, 11 , 13, 14 , 17 , 29, 30 , 36, 37, 45, 46 )

Material Examined. Holotype ( Figs 1, 2 ). ♂ ‘ TAIWAN: NANTOU Co., Xitou , 1100m, 21.VII.2015, reared from Camellia sinensis ( HSU 15 G16M), pupated 23.VII.2015, emgd. 16.VIII.2015, Y.C. Lin and R. J. Lin’ [white label, printed] , ‘ Holotype Epsteinius translucidus Lin’ [red label, printed] ( NHM) .

Paratypes. 2 ♂, 6 ♀. 1 ♂ labeled similarly to holotype but with date ‘ 25. VI.2013 ’, ‘( HSU 13 F15M)’ and ‘emgd. 19.VII.2013 ’; 1 ♂ labeled similarly to holotype but with date ‘ 19.IX.2018 ’, ‘( HSU 18 J30M)’ and ‘pupated 5.X.2018 , emgd. 19.X.2018 ’; 1 ♀ labeled same as holotype; 2 ♀ labeled similarly to holotype but with date ‘ 19. IX.2018 ’, ‘( HSU 18 J30M)’, and ‘pupated 30.IX.2018 , emgd. 24.X.2018 ’ and ‘pupated 8.X.2018, emgd. 3.XI.2018 ’; 3 ♀ labeled similarly to holotype but with date ’ 18. VI.2019 ’, ‘( HSU 19 F41M)’, and ‘emgd. 20.VII.2019 ’, ‘emgd. 24.VII.2019 ’, and ‘emgd. 6.VIII.2019 ’ ( NTNU) .

Description. Male ( Figs 1, 2, 11 , 36, 37 ): Head: frons hairy, brown; eyes semi-oval, grey with black center; labial palpus porrect, with 2 nd segment pointed upwards and 3 rd segment short, orange with brown patch; galeae small, partially covered by labial palpus; antenna filiform. Thorax: dark brown dorsally, pale-orange ventrally; legs orange with brown scaling, banded by brown on tarsi, hind leg tibia with four slender spurs, two in the middle and two at the end. Forewing: 5.3–5.5 mm long (from base to apex 5.4 ± 0.1 mm, n = 3); upperside orange-brown with irregular dark brown markings, becoming more pronounced towards base, with purple iridescent suffusion (more visible when alive), a broad dark brown submarginal band, scale fringe orange; underside ground color dark grey, broadly pale grey along dorsum, costa orange, a narrow black submarginal band, followed by a narrow orange terminal band, scale fringe orange with grey near tornus. Hindwing: upperside dark grey black, scale fringe grey; underside ground color pale yellow-grey, dorsum broadly grey, scale fringe grey.

Female ( Figs 3, 4 , 45, 46 ): similar to male, but larger, forewing 5.5–6.6 mm long (from base to apex 6.1 ± 0.5 mm, n = 5). The 5 th tarsomere with a long triangular recessed pad ( Fig. 45 ) bearing sensilla and spinules ( Fig. 46 ).

Male genitalia ( Figs 13, 14 ): Uncus rather short, narrowly pointed, dorsally with few long hairs near base. Gnathos originating high on tegumen, weakly down-curved, fused before middle with short, blunt dorsal process from junction, long slender distal half with sharply down curved tip. Vinculum ventrally ill-defined, membranous. Valva distally narrowing and up-curved, inner surface densely hairy except near base; a long, distally up-curved, band-like process from inner dorsal margin of valva, and below a straight thorn-like process from base of valva; a sacculus-like process from ventral base of valva, consisting of a bulbous base terminating in a large curved gradually tapering horn-shaped spine reaching beyond dorsal margin of valva. Juxta weakly sclerotised. Phallus short, very wide and rounded at base and gradually narrowing to down-curved, strongly sclerotised ventral apex; vesica with two large cornuti, consisting of a more basal folded and apically curved sclerite and a more distal spine-like sclerite from a wide base.

Female genitalia ( Fig. 17 ): Anal papillae flat, semicircular; posterior apophyses very long and slender, anterior apophyses very short and stout; lamella postvaginalis a deeply concave spinulose membrane, lamella antevaginalis with a long conspicuously spinulose knob centrally, flanked by a small plate on each side. Ductus bursae gradually widening from ostium, membranous, longitudinally plicate, narrowed before junction with corpus bursae. Corpus bursae ovate, small, half length of ductus bursae, with two large signa, each a convex plate with a row of flat complex teeth across its center.

Immature stages ( Figs 24–33 ): Final instar larva ( Figs 26, 27, 31, 32 ) 6.5–7.8 mm in length (7.1 ± 0.5 mm without spine length, n = 7), 3.2–4.7 mm in width of A3 (3.9 ± 0.5 mm without spine length, n = 7). Head brown. Body slug-like with no spine on T1; one spine and one seta on a protuberance for each D1 and D2, one spine on a protuberance for SD of T2; two spines on a protuberance for D, one spine each on a protuberance for D2 and SD of T3; two spines on a protuberance for D, one spine on a protuberance for SD of A1–A8; one spine and two setae on a protuberance for D of A9; no spine on A10. Coloration of body semi-translucent whitish-green in early instars ( Figs 24, 25 ), becoming semi-translucent green in final instar, some individuals with an indistinct brown patch laterally on A3–A4. Cocoon ( Fig. 28 ) spheroid, 5.1–6.0 mm in long axis (5.3 ± 0.5 mm, n = 5) and 3.3–4.2 mm in short axis (3.8 ± 0.3 mm, n = 5), brown. Pupa ( Fig. 40 ) 3.9–4.6 mm in length (4.3 ± 0.3 mm, n = 3), 2.2–2.4 mm in width (2.3 ± 0.1 mm, n = 3); pupal eyepiece with a fracture line ( Figs 41–42 ).

Etymology. The specific name translucidus is derived from the Latin word trans, which means through or across, and the Latin word lucidus, which means under light or full of light. The species group name refers to the semi-translucent coloration of the larva, and is a compound descriptive name comprising an adjective combination with the ending of the second name in masculine form to agree with the gender of the generic name.

Distribution. Epsteinius translucidus is currently known only from montane areas of central Taiwan at an altitude from 800 to 1100 m.

Biology. Larvae have been found on Camellia japonica L. (HSU 13F16M and 13K14M) and C. sinensis (L.) Kuntze (HSU 13F15M, 13K13M, 15G16M and 18J30M) ( Theaceae ) in June, July, September and October. Of the nine larvae reared in captivity, the pupal stage varied from 14–30 days. These observations suggest there are at least two generations annually, with adults emerging in summer (July–August) and again in autumn (October–November).

The larva of E. translucidus is semi-translucent, and it usually rests on the abaxial leaf surface. Whilst feeding on the underside of a leaf, the edge of the body is almost transparent, making the larva exceedingly difficult to detect. The feeding behavior is also unusual: most limacodid larvae consume the entire leaf, eating the epidermis only in the early instars ( Cock et al., 1987); however, E. translucidus retains the feeding pattern typical of early instars throughout its entire life and never eats the whole leaf. This unusual feeding pattern results in the leaf having a skeletonized appearance ( Fig. 33 ). The final instar larva of E. translucidus closely resembles the skeletonized leaf and thus presumably relies on crypsis to avoid predation, unlike many other nettle caterpillars that rely on aposematism and an array of conspicuous poisonous spines.

Predation is an important selective pressure and some prey have evolved cryptic coloration to reduce the likelihood of being visually detected and eaten ( Webster et al., 2015). Transparency is a common strategy for aquatic organisms in mid-water environments to mimic the background and to decrease detectability by visual predators ( Kerfoot, 1982; Langsdale, 1993; Tsuda et al., 1998). However, in terrestrial organisms, transparency is a relatively rare adaptation for avoiding predation. Larvae of E. translucidus appear semi-transparent and rest on the abaxial side of a leaf, and thus, represent an interesting case in which crypsis is based on transparency through its body color, resting behavior, and feeding pattern.

Figures

FIGURES 1–12. Adults of Epsteinius translucidus and Microleon longipalpis: 1, 2, E. translucidus Lin, sp. nov. holotype male upper side and underside; 3, 4, E. translucidus Lin, sp. nov. paratype female upper side and underside; 5, 6, M. longipalpis male upper side and underside; 7, 8, M. longipalpis female upper side and underside; 9, 10, M. longipalpis holotype male upper side and label data (Yokohama, Japan) (NHM); 11, 12, male heads of E. translucidus Lin, sp. nov. and M. longipalpis.

FIGURES 13–16. Male genitalia of Epsteinius translucidus and Microleon longipalpis: 13, 14, genitalia (ventral) and phallus (lateral) of E. translucidus Lin, sp. nov.; 15, 16, genitalia (ventral) and phallus (lateral) of M. longipalpis.

FIGURES 17–18. Female genitalia of Epsteinius translucidus and Microleon longipalpis: 17, E. translucidus Lin, sp. nov.; 18, M. longipalpis.

FIGURES 19–33. Life history of Epsteinius translucidus and Microleon longipalpis: 19–23, M. longipalpis, showing dorsal and subdorsal views of early instar larva, dorsal view and subdorsal views of final instar larva, and cocoon without reverse neat and circular cut after adult emergence; 24–33, E. translucidus Lin, sp. nov.; 24–25, early instar larva, showing dorsal and subdorsal views; 26–27, final instar larva with brown lateral patch, showing dorsal and subdorsal views; 28, cocoon, without reverse neat and circular cut after adult emergence; 29–30, adult female, showing lateral and ventral views; 31–32, final instar larva without brown lateral patch, showing dorsal and subdorsal views; 33, final instar larva on host plant, showing transparent edge of larval body from abaxial leaf surface under sunshine.

FIGURES 34–46. Head, pupa, and female 5th tarsomere of Epsteinius translucidus and Microleon longipalpis: 34–35, head with right labial palpus and galeae of M. longipalpis; 36–37, head with right labial palpus and galeae of E. translucidus Lin, sp. nov.; 38–39, eclosed pupa and ruptured pupal eye of M. longipalpis (arrow denotes fracture line); 40–42, uneclosed pupa, uneclosed pupal eye, and eclosed ruptured pupal eye of E. translucidus Lin, sp. nov. (arrow denotes fracture line); 43–44, female 5th tarsomere and sensilla of M.longipalpis; 45–46, female 5th tarsomere and sensilla of E. translucidus Lin, sp. nov..