Helenoscoparia nigritalis, (Walker, 1855) (Walker, 1875)

Karisch, Timm & Fowler, Liza, 2021, Description of the larva of Helenoscoparia nigritalis (Walker, 1855) (Pyraloidea: Crambidae: Scopariinae), Metamorphosis 32 (1), pp. 15-23 : 16-20

RESULTS

The specimens from St Helena were identified from their barcodes as H. nigritalis with a likelihood of more than 99 %, the specimen from Sollnitz as E. lacustrata (Panzer, 1804) with a likelihood of 100 %. The barcodes of our material are stored in BOLD.

Description of the larvae

Larva, particularly the tergites, dirty yellowish or pastel green; head, prothoracic shield and pinacula blackish or very dark brown; last instar 8–11 mm long.

Head ( Figs 2 , 3 ): Orthognathous, brown; epicranial suture present; frons with P1 about half as distant from AF1 as from P2, P2 closer to V1 than to P1; AF1 slightly more dorsal in the adfrontal area, AF2 slightly dorsal of lower end of median suture; F1 closer to ventral margin of frontal area than to the middle; C1 on lateral end, C2 straight below F1 at clypeus margin; clypeus margin with distinct undulations; A1, A2 and A3 forming a nearly right-angled triangle, distance between A1 and A2, A2 and A3 nearly equal, between A1 and A3 about 1.5 times longer; L1 above upper stemma, fairly close to A3; six stemmata, arranged in a semicircle, anterior part with three attached stemmata, the others isolated; O1 just below the middle of the distance of stemma 2 and the three attached stemmata, O2 oblique below stemma 1; SO2 and SO3 ventral between stemmata 5 and 6.

Thorax ( Figs 4 , 5 ):

Prothoracic shield with long XD1 and XD2, XD2 closer to SD1 than to XD1; SD1 closer to SD2 than to XD2, with longer seta than SD2; dorsal setae D1 and D2 fairly long, about the same separation as XD1 and XD2, positioned in postmedian area of shield; prespiracular plate formed as a lateral plate, bisetose, L1 and L2 at anterior margin; subventral pinaculum bisetose, setae long, approximated. Thoracic segments 2 and 3 each with broad, semi-circular dorsal pinaculum with two strong and long dorsal setae (D1 and D2) and two long, approximated subdorsal setae (SD1 and SD2); three long lateral setae, two very close at anterior pinaculum, another further apart on posterior pinaculum; a single seta on subventral pinaculum (SV1); four fairly short setae at the semi-circular sclerotisation at the base of the legs, and one very short seta just caudal of that sclerotisation; femurs and tibias with four setae each.

Abdomen ( Figs 5 , 6 ):

A1–2: dorsal, subdorsal and subventral pinacula unisetose; lateral pinaculum bisetose; ventral with two pinacula, medio-ventral with three shorter and approximated setae, ventrally with one short and fine seta.

A3–6: one long seta on each dorsal and on the subdorsal pinaculum, lateral (subspiracular) pinaculum bisetose; subventral pinaculum with stronger SV1; base of prolegs with two semicircular sclerotisations, medio-ventrally with three setae, MV2 slightly closer to MV1 than MV3 to MV1, ventral sclerotisation unisetose.

A7: long, strong D1 and D2, D1 slightly anterio-lateral on pinaculum, subdorsal plate unisetose; lateral (subspiracular) pinaculum bisetose; subventral pinaculum with one rather long central seta; medio-ventral pinaculum bisetose, ventral pinaculum unisetose.

A8: long, strong D1 and D2, D1 lateral on pinaculum; subdorsal plate unisetose; lateral (subspiracular) pinaculum bisetose; subventral pinaculum with one rather long central seta; medio-ventral pinaculum unisetose, ventral pinaculum unisetose.

A 9: dorsal pinaculum with very long D 1 in postmedian half; subdorsal pinaculum with stout SD 1 in dorsal area and fine, rather long SD2 posterio-ventrally; L1 long, strong, placed more posteriorly; medio-ventral and ventral pinacula unisetose.

A 10: D1 long; L1–3 very long, in slightly dorsally arched line; SV1–4 rather stout, SV1 closer to SV2, SV2, 3 and 4 nearly evenly spaced; several ventral setae.

Pupa ( Figs 7–8 ):

6–7 mm; amber; palpi maxillares distant from maxillae; mandibulae quite large, nearly triangular; palpi labiales open; proboscis longer than forelegs, slightly shorter than middle legs; at the end of the abdomen broad ventrolateral protrusions; end of abdomen bell-shaped, with two pairs of strong, straight, rather long bristles.

With exception of the more distinct end of the abdomen with the two pairs of strong bristles the pupa fits well with the characters of pupae of Scopariinae , given by Patočka (2001).

Remarks

Larvae of E. lacustrata ( Figs 9 , 10 ) and S. ambigualis are ( Fig. 11 ) very similar to one another and differ mainly in the form of the prothoracic shield and the prespiracular and subventral pinacula. The differences between H. nigritalis and the two European Scopariinae are much more obvious ( Table 1 ).

Notable are the different shape of the prothoracic shield, the extended lateral sclerotisation of the whole spiracular area and the stronger sclerotisations in the subventral part of the integument and around the bases of the legs. In H. nigritalis the dorsal pinacula of A2 and A3 are fused with the subdorsal pinacula and form a broad, semicircular sclerotisation. In E. lacustrata and S. ambigualis subdorsal and dorsal pinacula are well separated and comparatively small. Furthermore in E. lacustrata the sclerotisations at the bases of the legs are less extensive as in H. nigritalis .

On the other abdominal segments, the sclerotisation of the anterior dorsal pinacula is more extended than in the European species. The lateral pinacula are different in shape on A3–6. In contrast to the distinct size and shape of several pinacula, the number and arrangement of setae is very similar in H. nigritalis , E. lacustrata and S. ambigualis .

Judging from the size, shape and arrangement of pinacula, a distant position of the St Helenian species of Scopariinae from the Europeans seems to be justified and therefore the separate genus Helenoscoparia is confirmed by our study of the larva.

From the description of the subfamily given by Hasenfuss (1960) we confirm that in H. nigritalis AF 2 is located below P2; P1 is closer to P1 (on the other side of the body) than P2 to P2; stemmata 4, 6 and 5 are positioned in a right angle; A3 is closer to stemma 2 than to stemma 1. AF1 to AF2 is about the same distance as AF1 to F1. The right or acute angle formed by O1–O3 was not found, either in the illustration in Hasenfuss (1960: Fig. 181) or on the larva of H. nigritalis .

Prothorax: XD2, SD1 and SD2 form a right angle as described in Hasenfuss (1960) and SD1 is further from SD2 than from XD2. SV1 is macroscopic, and the distance between D1 and D1 (on the opposite side) is shorter than between D2 and D2. L2 is dorsocaudal from L1 and on A8 the line from D1 to SV1 passes in front of the stigma, and the line from SV1 to L2 passes behind the stigma. On A1 and A2 there are three MV-setae. On A9 setae L1 and SV1 are absent; SD2 is very fine and D1 is dorsocranial to it; setae D1 are on a single pinaculum and the distance D1– D1 is shorter than D1–SD2. Concerning the position of the ventrolateral setae of A10, further studies on more material of H. nigritalis are necessary. With regard to the size of the stigma and the length of the setae D1, D2, L1 and L2, H. nigritalis fits Hasenfuss’s (1960) description of Scoparia .

Biology and ecology of the larva

Larvae of H. nigritalis have been found in several different micro-habitats. We assume that it accepts a broad range of habitats, if sufficiently damp. The larva was first observed in the thin layer of soil and humus between the lower surface of the lichen Parmotrema reticulatum (Taylor) M. Choisy on big rocks ( Fig. 12 ) in the zone of the former cloud forests, now mainly covered with introduced ferns and vascular plants, especially New Zealand Flax ( Phormium tenax J.R. & G. Forst).

On 3 rd Nov. 2019, a second habitat was discovered on the surface of soil in the shade of Eucalyptus trees and under fallen dead leaves of Eucalyptus around a house at Burnt Rock at 500 m. a.s.l. ( Fig. 13 ).

Larvae were also found next to a chicken coop. Webbings partially covered areas with Bryum argenteum Hedw. and Ceratodon purpureus (Hedw.) Brid. On 30 th Nov. 2019, larvae were traced in webbing over moss ( Bryum dichotomum Hedw. and B. argenteum ) growing from a leaking water tank ( Fig. 14 ) at Burnt Rock.

Subsequently, larvae have been observed by the second author amongst mosses in different types of forest. In the Eastern part of the island there are semi-arid habitats with sparse vegetation where larvae seem to prefer the soil surface under plants or in places where water is dropping from the leaves [L.F.’s observations at Horse Point ( Fig. 15 ), and Isaac, Fowler & Stevens 2018]. In all places the larvae were found moving in thin silky tunnels in webbing. When the webbing was turned over, the caterpillars often clung to the web ( Fig. 16 ). A few larvae crawled away and hid in silky holes in the soil crust.

The larvae from Cabbage Tree Road were fed with P. reticulatum and pupated successfully and hatched, although the moths were comparatively small. Larvae were only seen at night at Cabbage Tree Road, but everywhere else larvae were also active by day. Besides the lichen, the larvae were also seen feeding on several species of moss, including those mentioned above ( Fig. 14 ). On a shade net covering a chicken coop at Burnt Rock, larvae were found to feed on (probably) algae and protonema stages of mosses ( Fig. 16 ).

Pupae were found at Cabbage Tree Road in the substrate where larvae were living ( Fig. 7 ). Because the moths hatched during transport in sealed bags, further research is necessary to determine the duration of pupation.

Figures

Figure 2 – Head of H. nigritalis (anterolateral).

Figure 3 – Head of H. nigritalis (lateral).

Figure 4 – Head and first thoracal segments of H. nigritalis (lateral).

Figure 5 – Integument of H. nigritalis.

Figure 6 – 10th abdominal segment of E. lacustrata.

Figure 7 – Pupa of H. nigritalis in substrate at Cabbage Tree Road (2017, photo D. Pryce).

Figure 8 – Pupa of H. nigritalis, ventro-lateral view.

Figure 9 – Integument of larva of E. lacustrata..

Figure 10 - 10th abdominal segment of E. lacustrata.

Figure 11 – Larva of S. ambigualis; a – lateral, b – dorsal, c – caudal [after Smith 2004; reproduced from Entomologist’s Gazette 55 (2004) with kind permission].

Figure 12 – Larva of H. nigritalis under lichens at a rock at Cabbage Tree Road near Taylor’s (2018, photo D. Pryce).

Figure 13 – Larva of H. nigritalis at the underside of a Eucalyptus leaf, Burnt Rock (2019, photo L. Fowler).

Figure 14 –H. nigritalis larva in a silky tunnel in the soil at Burnt Rock, with particle of moss (2019, photo L. Fowler).

Figure 15 – Webbings of H. nigritalis in moss at a water tank at Burnt Rock (2019, photo L. Fowler).

Figure 16 – Shade web of chicken coop with trace of frass of H. nigritalis larva (2020; photo L. Fowler).