Research Article |
Corresponding author: Lu Jiang ( jianglu@syau.edu.cn ) Academic editor: Emmanuel Arriaga Varela
© 2024 Xiao-Yu Sun, Xu-Ming Dong, Lu Jiang.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Sun X-Y, Dong X-M, Jiang L (2024) Larval morphology of a Palearctic Rutelini, Parastasia ferrieri (Coleoptera, Scarabaeidae), with discussions on their feeding habits. Deutsche Entomologische Zeitschrift 71(1): 185-192. https://doi.org/10.3897/dez.71.113727
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Rutelini is one of the largest tribes of Rutelinae, widely distributed but primarily in the New World. Recently, both larvae and adults of Parastasia ferrieri had been discovered in Liaoning Province of northeastern China from the Palearctic realm. The third-instar larvae of P. ferrieri were described using light and scanning electron microscopy in order to discover more morphological characters for larval taxonomy. The larvae of P. ferrieri exhibit remarkable features, including four protuberances on labrum, no helus on epipharynx, two scissorial teeth on each mandible, five stridulatory teeth plus a blunt protuberance on each maxilla, and the obtuse claws on the thoracic legs. The correlation between morphological features and feeding habits is briefly discussed.
saproxylic, shinning leaf chafer, SEM, ultramorphology, white grub
Rutelinae, commonly known as shining leaf chafers, are so named due to the bright colors of most of their species and their adults feeding on plant leaves (
Larvae of Rutelinae are commonly referred to as white grubs, exhibiting diverse feeding and living habits at the tribal level (
The Rutelini encompass approximately a thousand species assigned into 93 genera, with a primary presence in the New World (
Parastasia is one of the largest genera within Rutelini, comprising approximately 105 species worldwide (
In this study, third instar larvae of P. ferrieri were obtained through rearing. Their morphology is described using light and scanning electron microscopy in order to better understand the morphological diversity within the group and help with the identification of larvae in this genus.
Larvae of P. ferrieri were collected from Qipanshan Forest Park in Shenyang City, Liaoning Province of northeastern China, in late October 2019. A total of 13 adult P. ferrieri beetles (Fig.
To conduct morphological observations, a total number of ten larvae were fixed in Dietrich’s solution (formalin: 95% ethanol: glacial acetic acid: distilled water = 6: 15: 1: 80, v/v), which was heated up to 70 °C and then left to cool naturally for 12 h under a fume hood before being preserved in 75% ethanol (
Photographs were captured using a SONY ILCE–7RM4 digital camera. Scanning electron microscopy (SEM) was employed to examine third instar larvae. These larvae were dissected and examined in 75% ethanol using a Leica EZ4HD Stereoscopic Zoom Microscope. After a two-minute ultrasonic cleaning and two rinses in 75% ethanol, they were prepared for SEM. Dissected organs underwent serial dehydration using graded ethanol, followed by replacement with tertiary butanol. They were then subjected to freeze-drying for 3 hours, sputter-coated with gold, and examined under a Hitachi S–3400N scanning electron microscope (Hitachi, Tokyo, Japan) at 5 kV. Nomenclature for larval morphology follows (
Voucher specimens of both adults (Fig.
Larvae are of typically scarabaeiform shape, bearing three pairs of thoracic legs on the C-shaped body (Fig.
The head capsules are 3.1 ± 0.15 mm (N = 10) in width. The larval head displays symmetrical adornment, boasting a total of 14 pairs of setae. These include two pairs aligned vertically on the clypeus, five pairs in the frontal region (comprising two pairs of posterior frontal setae and three pairs of anterior frontal setae), three pairs on the vertex, and four pairs in the genal area (Fig.
Larval head of Parastasia ferrieri. A. Head; B. Labrum; C. Antenna; D. Sensilla on the apex of antenna. AFS, anterior frontal seta; AT, antenna; CLP, clypeus; DES, dorsoepicranial setae; ES, epicranial stem; F, frons; FCS, frontoclypeal suture; LB, labrum; LP, labral protuberance; PFS, posterior frontal seta; SB, sensillum basiconicum.
The antenna is elongated and slender, comprising four segments, with the second segment being the longest (Fig.
The mouthparts are of a biting-chewing type, consisting of a labrum, a pair of mandibles, and a maxilla-labia complex.
Labrum exhibits symmetry and is slightly wider than it is long. The outer surface of the labrum displays symmetrical features, including four prominent protuberances and seven pairs of setae (Fig.
Epipharynx, membranous, situated on inner surfaces of labrum and clypeus. Epipharynx is further divided into distinct functional areas (Fig.
The paired mandibles are heavily sclerotized, bearing two anterodorsal setae and a row of 11 setae on the lateral surface (Fig.
Mandibles and maxillae of Parastasia ferrieri. A. Left mandible, dorsal surface; b Right mandible, dorsal surface; C. Right mandible, ventral surface; D. Left mandible, ventral surface; E. Maxillae and labia, ventral surface, insert showing the magnification of maxillary palpus; F. Maxilla, labia, and hypopharynx, dorsal surface. AC, acia; CAR, cardo; DC, dorsal carina; DO, digitiform organ; GL, glossa; HS, hypopharyngeal sclerome; IC, incisor; LL, lateral lobe; LP, labial palpus; M, mola; MP, maxillary palpus; PC, penicillus; PM, postmentum; PR, precoila; PRM, prementum; SC, scobis; ST, stridulatory teeth; STA, stridulatory area; SP, stipes; TP, truncate process; VP, ventral process.
The maxillae, labia, and hypopharynx are fused together to form a structural complex (Fig.
Each of the thoracic legs is composed of five segments: coxa, trochanter, femur, tibiotarsus, and a distal single claw (see Fig.
Thoracic legs, spiracles and raster of Parastasia ferrieri. A. Prothoracic leg, lateral view; B. Prothoracic spiracle; C. Raster; D. Magnification of the anterior palidia; E. Magnification of the hamate seta. BU, bulla; CL, claw; CX, coxa; FM, femur; RSP, respiratory plate; SS, spiracular slit; TT, tibiotarsus; TR, trochanter.
The respiratory plate is composed of numerous minute openings that encircle the oval bulla, along with a slightly curved spiracular slit (refer to Fig.
The raster is furnished with paralleled palidia, each composed of a longitudinal patch of mesal directed pali, surrounding a prominent septula. The palidia are submerged in a large number of setae, which are slightly longer and distributed at the lateral region.
In this study, larvae of P. ferrieri were described using scanning electron microscopy for the first time. The larvae of P. ferrieri are remarkable for the following structures: bearing four protuberances on labrum; no helus on epipharynx; two scissorial teeth on each mandible; five stridulatory teeth and a blunt protuberance on each maxilla; obtuse claws on thoracic legs, and 12 pairs of pali on raster. By the combination of these characters, larvae of P. ferrieri can be readily distinguished from most of the other larvae in Rutelini (
The labrum exhibits a wide range of morphological features within families or subfamilies of Scarabaeidae (
Previous comprehensive studies (
Mandibles, being the most heavily sclerotized structures on mouthparts, are structurally correlated with feeding habits (
The claws of thoracic legs show considerable morphological diversity across lineages (
Rutelinae usually attract attention due to their exquisite adult appearances or the economic losses caused by their larval stages (
Conceived and designed the experiments: LJ, XYS. Performed the experiments: XYS, XMD. Analyzed the data: XYS and LJ. Wrote the paper: XYS, XMD and LJ.
We are grateful to Ming-Zhi Zhao and Zi Shan for their kind help during our larval collecting and rearing periods. Our special thanks go to Dr. Yuan-Yuan Lu and Dr. Valentina Filippini for their valuable suggestions on our earlier draft. This research was financially supported by the National Natural Science Foundation of China (grant no. 32370470 and 31702036), China Postdoctoral Science Foundation (grant no. 2020M680982), Natural Science Foundation of Liaoning Province (2021-MS-230), Scientific Research Project of Education Department of Liaoning Province (LJKZ0641), Science and Technology Planning Project of Liaoning Province (grant no. 1618214601077) and Scientific Research Foundation for the Introduced Talent of Shenyang Agricultural University (grant no. 880417008).