Die Präimaginalstadien von Rinaca simloides Naumann, Nässig & Löffler, 2018 von Vietnam (Lepidoptera: Saturniidae)

"Abstract: The life-history of Rinaca simloides NAUMANN, NÄSSIG & LÖFFLER, 2018 (Saturnia (Rinaca)) from the Axan Mountain, 1,300 m, in the Tây Giang district of the Quảng Nam Province in the South Central Coast region of Vietnam is described and figured for the first time and compared with Rinaca simla (WESTWOOD, [1847]) (Saturnia) from Thailand and China. The authors found that the two taxa cannot be distinguished by the morphologies of their pre-imaginal instars alone. Since there are only minor or no obvious morphological differences between the adults of R. simloides and R. simla, we consider a separation of some Central and South Vietnamese populations as a distinct species to be doubtful rather. The taxonomic status of R. simloides is not deeper discussed here but further studies are considered needed (see “Taxonomical note”).

Rearing data and observations: The indoor rearing of R. simloides was carried out by the authors successfully by using Carpinus betulus L. (Betulaceae) as substitute host plant. Eggs were received in late January 2021 and stored in the fridge at 6° Celsius. Larvae hatched after the eggs have been put in the warm room. The first larva hatched on 29.iv.2021. The 1st molting took place on 09.v.2021, the 2nd molting on 15.v.2021, the 3rd molting on 23.v.2021, the 4th molting on 02.vi.2021, and the 5th molting on 12.vi.2021 (molting date of the first larva in each instar). Six larval instars were observed. The first cocoon was spun on 15.vii.2021. The data recorded under laboratory conditions are considered being most probably different from data which might be observed in the wild. The larvae were reared in open plastic container under varying indoor humidity and temperatures (18-23°C).

Descriptions of the immature stages of R. simloides (Central Vietnam):

Ovum (fig. 6): Length approximately 2.30 mm, width 1.55 mm and height (thickness) 1.43 mm, thickness of the eggshell about 0.025 mm. The egg is elongated barrel-shaped. The ends are strongly curved outwards. The larva hatches at one end. The almost round opening measures around 0.75 mm. The tiny structures on the surface of the egg shell cannot be identified at 80x magnification. Ground coloration whitish or pale brown; the egg is covered with a brown to darkbrown secretion for afixing the egg to the substrate. The eggshells are generally not eaten. All measurements were taken with the OLYMPUS® Stereo Zoom Microscope SZ40 fitted with the measuring eyepiece GWH10X-CD. Digital pictures were taken with OLYMPUS® E-M1 Mark III fitted with OLYMPUS® M.ZUIKO DIGITAL ED 60mm 2.8 Macro lense or OLYMPUS® M.ZUIKO DIGITAL 30mm 3.5 Macro lense (this is not an advertisement!).

1st instar larva (figs. 7-9): Head capsule matt black with a width (measured diagonally over the eyes) of 0.88-0.98 mm and an average width of 0.93 mm (n=6). Thoracic legs reddish-black, the thoracic segments matt black ventrally, abdominal legs and anal prolegs ventrally ocher yellow as well as the abdominal segments ventrally, anal prolegs black laterally, thoracic and abdominal segments black dorsally and laterally. All scoli are black but not the subspiracular scoli of the abdominal segments, which are connected with a yellow line and are pale brown colored. Spiracles tiny, brown colored. Scoli usually arranged in six longitudinal rows, those of the thoracic segments in 8 rows, and those of the 9th abdominal segment in 4 rows. The anal plate is with 2 scoli. All scoli bearing whitish or dark brown to black bristles of the “star wart” type on their apices and long hairs. The head capsule is with short whitish bristles, all subspiracular scoli bearing whitish bristles and much longer whitish hairs facing downwards to the substrate or aft from the 9th abdominal segment, the scoli of the prothorax bearing whitish bristles and longer hairs facing cephad. All other bristles are dark colored.

2nd instar larva (fig. 10): Clearly different from the previous instar. Head capsule light brown with whitish primary setae. Width of the head capsule 1.43-1.49 mm, average 1.45 mm (n=3); that means an average increase in width by 55.91 % from the previous instar. Thoracic legs light brown, anal and abdominal prolegs are yellow. Prothorax whitish, integument dorsal and subdorsal whitish, a black or almost black stripe is connecting subdorsal scoli from the mesothorax towards the anal segments. A turquoise stripe is running from the mesothorax towards the 8th abdominal segment laterally. Both stripes are less conspicuous at the thoracic segments. The larvae are yellowish colored ventrally and ventrolaterally, except the thoracic segnments which are more ocher. Scoli are transparent ocher, subspiracular scoli yellow. Spiracles colored as body. Strong bristles are present as in the previous instar but transparent brownish, body covered with medium sized whitish hairs dorsally and at least one long fleshy whitish hair at the apex of each scolus. Numerous long whitish hairs are present at the subspiracular scoli. Light brown patch on the outside of each anal proleg.

3rd instar larva (fig. 11): Clearly different from the previous instar. Head capsule pale greenish with whitish primary hairs. Width of the head capsule 2.30-2.33 mm, average 2.17 mm (n=8); that means an average increase in width by 49.66 % compared to the previous instar. Ground color like in the previous larval instar, but the black lateral stripe is replaced by more extensive turquoise with small black dots remaining. Head capsule, thoracic legs and abdominal prolegs weak yellowish green, larva ventrally and ventrolaterally and all scoli colored as head capsule and legs. Outside of the anal prolegs light bluish with a black crescent moon shape border. Subspiracular scoli connected with a yellowish orange line. The bristles at the apices of scoli like in the previous instar. The larva is covered with long whitish fleshy hairs dorsally. The fleshy hairs of the prothorax facing forward and those of the subspiracular scoli are pointing down. Anal plate and prolegs are with short strong bristles.

4th instar larva (fig. 12): Clearly different from the previous instar. Width of the head capsule 3.10-3.40 mm, average 3.20 mm (n=6); that means an average increase in width by 47.47 % compared to the previous instar. Thoracic legs brown, abdominal prolegs green and anal prolegs green with a broad black border, patch on the outside of each anal proleg with tiny brown dots. Integument dorsal an subdorsal whitish, anal plate light green, laterally yellowish green but spiracles and the area around the spiracles turquoise, a yellowish orange line connecting the subspiracular scoli. Prothorax, thoracic segments and abdominal segments ventrally and ventro-laterally green. Short ventrolateral hairs, hairs of the anal segments and of the prothorax yellow colored, all other pale bluish. Long thin hairs as in the previous instar colored weak bluish, stronger long single hairs present at the apices of subdorsal scoli.

5th instar larva (fig. 13): Not much different from the previous instar. It only differs in a few details. Width of the head capsule 4.50-4.80 mm, average 4.63 mm (n=4); this means an average increase of the width of 44.69 % compared to the previous instar. Integument laterally yellowish green, turquoise patches around the spiracles slightly reduced, the line connecting the subspiracular scoli conspicuous reddish brown colored. The larva rolls up its thoracic and anterior abdominal segments when disturbed and increases its volume because of the thick hair.

6th instar larva (figs. 14-16): Not obviously different from the previous instar. Width of the head capsule ca. 6.50-7.00 mm, average 6.75 mm (n=4); this means an average increase of the width of 45.79 % compared to the previous instar. As in the previous instar the larva rolls up its thoracic and anterior abdominal segments when disturbed (sphinx-like position) and increases its volume because of the thick hair.

Cocoon and pupa: Cocoon and pupae do not differ from those of R. simla (India, China). Therefore the descriptions of both are lacking herein.

Taxonomic note: Rinaca simla (WESTWOOD, [1847]) (Saturnia) from Thailand and India, as well as Rinaca simloides NAUMANN, NÄSSIG & LÖFFLER, 2018 (Saturnia (Rinaca)) from the Axan Mts., 1,300 m, Tây Giang District, Quảng Nam Province, South-Central Region, Vietnam obviously do not differ in their larval morphologies. Larvae from China and Okinawa show an enlarged black pattern. Likewise, there are no obvious distinguishing features among the adults that would justify a description of R. simloides as an independent species. The description of R. simloides was based on DNA studies (COI marker gene), which were mentioned in the original description but the result (the tree) was not presented. No taxonomic changes are made here, but it is proposed here to double-check the taxonomic status of R. simloides from Central Vietnam with more material."