Abstract

Sirex wood wasps (Hymenoptera: Siricidae) constitute a group of economically significant xylophagous pests that cause substantial damage to forestry globally. Herein, we present a systematic revision of the Chinese Sirex species. Through phylogenetic analyses, some taxonomic ambiguities were resolved. Sirex chimera sp. nov. is described (type locality: Chifeng, Inner Mongolia). Two new synonyms are proposed: S. rufiabdominis Xiao & Wu, 1983 and S. sinicus Maa, 1949 are synonymized with S. nitobei. S. dux (Semenov, 1921) stat. rev. is confirmed as a distinct species rather than a subspecies of S. juvencus or S. cyaneus, with the male described for the first time. Re-examination confirms that previous Chinese records of S. imperialis represent misidentifications of S. nitobei. The Chinese Sirex fauna is revised to comprise nine valid species: S. chimera sp. nov., S. dux, S. ermak, S. juvencus, S. nitobei, S. noctilio, S. piceus, S. tianshanicus, and S. vates. Comprehensive re-descriptions and a key to species are provided.

Key words

phylogeny, taxonomy, xylophagous insects, systematics

1. Introduction

The horntail family Siricidae (Hymenoptera: Symphyta) is a group of wood boring insects containing more than 120 species in 10 extant genera worldwide (Taeger et al. 2010; Schiff et al. 2012). Members of this family are phytophagous and represent a basal hymenopteran lineage, playing an important role in understanding the evolution of the order (Klopfstein et al. 2013; Rasnitsyn 1980; Manukyan and Smirnov 2021). Most Siricidae species are distributed in the Northern Hemisphere, with several species also found in the Afrotropical region (Goulet 2014; Taeger et al. 2010; Smith and Schiff 2002). Several species are frequently intercepted at ports far outside their normal home range, and some are regarded as invasive alien species. For example, the Palearctic Sirex noctilio has invaded Australia, New Zealand, South Africa, and South America (Morgan 1968, Schiff et al. 2012; Leavengood and Smith 2013). Nevertheless, studies on the ecology and taxonomy of this economically important group remain limited, particularly for the Palearctic fauna.

As the type genus of the family, Sirex comprises 29 recognized species primarily distributed across the Palearctic and Nearctic realms, with marginal extensions into the Oriental region (Taeger et al. 2010; Schiff et al. 2012; this study). Notably, invasive pests within this genus (e.g., S. noctilio and S. juvencus) have spread to Australia, Africa and South America via transcontinental transport, (Schiff et al. 2012; Leavengood and Smith 2013; Li et al. 2021). Despite the ecological significance of this genus, the taxonomy of Sirex remains contentious due to the deficiencies of earlier literature, the lack of specimens, and diverse color forms within single species, which compound the problem of taxonomic status and uncertainty of identification characteristics for many species. Despite this, the morphology of the ovipositor lancet pits has proven critical for resolving New World Sirex taxonomy (Goulet 2012). Kjellander (1945) first applied this character to differentiate S. juvencus and S. noctilio females. After that, Viitasaari (1984) consistently adopted this character in the fauna of Siricidae of Finland and nearby countries. Recent works formally codified this feature in dichotomous keys (Goulet 2012). The introduction of DNA barcodes can effectively assist in addressing the difficulties caused by polymorphism in taxonomy and species identification, as well as in the discovery of cryptic species with similar morphology (Goulet 2012; Schiff et al. 2012).

While Western hemisphere Sirex species have been comprehensively revised with integrated morphological, molecular, and ecological data (Schiff et al. 2012), Chinese siricid taxonomy has stagnated since the last century, with many problems that need to be solved. Xiao et al. (1992) compiled keys for both males and females, and provided brief descriptions for nine Sirex species known in China at that time (i.e. S. rufiabdominis Xiao & Wu; S. nitobei Matsumura; S. juvencus (Linnaeus); S. vates Mocsáry; S. piceus Xiao & Wu; S. imperialis Kirby; S. tianshanicus Semenov; S. ermak Semenov and S. sinicus Maa). However, previous research has not yet clarified the taxonomic status of Chinese Sirex species, especially in the aspects of the absence of illustrations, imprecise descriptions in the keys, lack of examination of type specimens, and incomplete species descriptions. These shortages make the identifications of some specimens problematic and the status of some species unreliable. In the present study, we aim to make a taxonomical revision of Chinese Sirex through the combined methods of morphological and phylogenetic analyses based on molecular data. A total of nine species is included in this revision, with a new species described, two new synonyms proposed, and a species newly recorded from China. Detailed descriptions, illustrations, and akey are provided for eight of these species, all based on examined material.

The ninth species, S. vates Mocsáry, could not be included in our detailed morphological assessment due to the lack of available specimens. This species is known only from its original description, which is superficial and lacks information about the number and deposition of type specimens. Furthermore, no additional specimens have been collected since its initial description. Nevertheless, we have reviewed the original description and relevant literature to discuss its taxonomic status in our study.

2. Materials and Methods

2.1. Taxon sampling

Eight of the nine Sirex species distributed in China were examined for morphological descriptions, with the exception of S. vates, whose description relies solely on previous literature. Distribution and host plant records are limited to China in this study. Six of the nine species were included in molecular phylogenetic analyses, as S. tianshanicus and S. piceus were excluded from genetic studies due to limited material (only type specimens available for morphological examination). To contextualize the Chinese taxa, we integrated additional sequences from Sirex spp. retrieved from Sun et al. (2016), Wooding et al. (2013), Roslin et al. (2022), Malm and Nyman (2015), Sikes et al. (2017), and Lombardero et al. (2016) into our phylogenetic framework. Specimen metadata associated with molecular analyses, including sample name, collection details, and GenBank accession numbers, are provided in Table S1 and Table S2.

2.2. Morphological comparison

Morphological terminology aligns with Schiff et al. (2012). Specimens were photographed using a SONY A7M2 digital camera equipped with a LAOWA FF 100 mm F2.8 CA-Dreamer Macro 2X macro lens. Image stacking was performed using Helicon Focus 6.7.1, followed by post-processing in Adobe Photoshop CC (Adobe Systems Inc., San José, CA, USA).

2.3. DNA Extraction, PCR Amplification and Sequencing

Genomic DNA from wood wasps was extracted using the D0926 Insect DNA Isolation Kit (Omega Bio-tek Inc., Norcross, GA, US), according to the manufacturer’s instructions. DNA integrity was verified by 1% agarose gel electrophoresis, with quantification performed on a JY300C electrophoresis system and a JY04S-3C gel imaging analysis system (JUNYI Electrophoresis Co., Ltd, Beijing, China). PCR primers used are LCO1490: 5’-GGTCAACAAATCATAAAGATATTGG-3’ and HCO2198: 5’-TAAACTTCAGGGTGACCAAAAAATCA-3’. Reactions were performed in a total volume of 50 μL, containing 25 μL of 2 × GoTaq® Green Master Mix (Promega, Madison, WI, USA), 2 μL of each primer, 2 μL of DNA template, and 19 μL of ultrapure water. The reaction procedure was as follows: initial denaturation for 2 min at 94°C, followed by 35 cycles of denaturation at 94°C for 30 s, annealing at 45°C for 30 s, and extension at 68°C for 2 min, with a final extension at 68°C for 10 min. Purified PCR products were sequenced bidirectionally on an ABI Prism 3730XL sequencer (Applied Biosystems, California, USA). Sequences were assembled and edited using Seqman v.7.1 and the DNASTAR Lasergene Core Suite software package (DNASTAR Inc., Madison, WI, USA).

2.4. Molecular phylogenetic analysis

Raw sequences were aligned and proofread in BioEdit 7.0.9 (Hall, 1999), excluding any with chromatogram double peaks. BLASTn verified sequences against NCBI references. Amino acid translation (MEGA X (Kumar et al. 2018), invertebrate mitochondrial code) was used to screen for NuMts. Nonsynonymous mutations, stop codons, and indels were checked to further reduce cryptic NuMts (Song et al. 2008; Bertheau et al. 2011). The phylogeny was reconstructed through the Bayesian Inference (BI) method as implemented in Phylosuite (Zhang et al. 2020). We estimated the most appropriate nucleotide substitution model by ModelFinder (Kalyaanamoorthy et al. 2017) and GTR was selected for the best-fitting model for the present phylogenetic analysis. To resolve phylogenetic placements, an analysis based on partial coding sequence of COI gene was carried out to compare the Chinese Sirex and related taxa. Seven species (Urocerus spp., Xeris spp. and Tremex spp.) were selected as outgroups. All novel sequences were deposited in GenBank (accession numbers are PV290776–PV290840; PV300958–PV300985).

Figure 1.

The Bayesian phylogenetic tree of the Sirex species based on COI sequences, with Urocerus spp., Xeris spp., and Tremex spp. as outgroup. Colored backgrounds delineate the species. Values at nodes indicate the posterior probability. A ladderized form tree is provided in Figure S1, the metadata of the samples are provided in Table S1 and S2.

BI analyses consisted of two independent runs, each with four Markov chain Monte Carlo (MCMC), which ran for 10 million generations (sampled every 1000^th generation with a 25% burn-in) to calculate the clade posterior probabilities (PP). The average standard deviation of split frequencies (ASDF), the potential scale reduction factor (PSRF), and the effective sample size (ESS) were used to evaluate the potential convergence of the BI analysis. Convergence was considered plausible when ASDF approaches 0, PSRF approaches 1, and ESS >> 200. Pairwise Kimura two-parameter (K2P) genetic distances (Kimura 1980) were computed in MEGA v.6 (Tamura et al. 2013).

3. Results

3.1. Phylogenetics analysis of Sirex species

To clarify the monophyly and phylogenetic relationships of Chinese Sirex species, we conducted a phylogenetic analysis using partial COI sequences from six Chinese species and 11 species distributed in the Western Hemisphere (Fig. S1). The results demonstrated strong support for the monophyly of all species, with high posterior probabilities (PP > 96).

Pairwise Kimura 2-parameter (K2P) genetic distances between Sirex and outgroup genera are ranged from 0.22 to 0.34 (Fig. 2). Interspecific divergence within Sirex is ranged from 0.02 to 0.21. Minimum divergence (0.02) was observed between S. nitidus and S. dux. In contrast, the maximum divergence (0.21) occurred between S. ermak and S. longicauda. Chinese species showed intermediate divergence levels, with K2P distances ranging from 0.07 to 0.13. Notably, while most genetic distances comparisons among Chinese species exceeded 0.1, S. nitobei and S. chimera exhibited lower divergence (0.07).

Figure 2.

The Kimura 2-parameter (K2P) distances (in percentage) Matrix between taxa. Species names of Chinese taxa are highlighted in pale red, other Sirex species in light blue, and outgroup taxa in gray.

3.2. Keys to Sirex species distributed in China

3.2.1. Key to females

1	Basal flagellar segments of antennae dark brownish or blackish (Figs 3, 4)	2
1’	Basal flagellar segments of antennae bright yellowish (Fig. 3G)	S. juvencus (Linnaeus, 1758)
2	Apical half of forewing darkened or with brownish spot/band near pterostigma (Figs 14A, 15A–D)	3
2’	Forewings mostly clear, at most tinted light brown near outer margin (Figs 11, 12)	5
3	Forewings with vein 3A basally present (Fig. 13B); pits near middle annuli of ovipositor less than 0.10 times as long as an annulus (Fig. 10C)	S. ermak (Semenov, 1921)
3’	Forewings with vein 3A completely absent (Figs 11, 12); pits near middle annuli of ovipositor at least 0.13 times as long as an annulus (Fig. 10)	4
4	Pits on genae 3–9 times distant compared to diameter of pits (Fig. 6K); tarsal pad of metatarsomere 2 0.3–0.4 times as long as ventral length of tarsomere (Fig. 7F); pits near middle annuli of ovipositor at least 0.4 times as long as an annulus (Fig. 10F)	S. noctilio Fabricius, 1793
4’	Pits on genae 0.1–2.5 times distant compared to diameter of pits (Fig. 6I); tarsal pad of metatarsomere 2 0.7–0.8 times as long as ventral length of tarsomere (Fig. 7E); pits near middle annuli of ovipositor at most 0.3 times as long as an annulus (Fig. 10E)	S. nitobei Matsumura, 1912 (see Note above)
5	Legs predominantly blackish (Figs 11, 12)	6
5’	Legs predominantly bright yellowish or reddish brown (Figs 12, 14)	7
6	Abdomen blackish with dark blue or purple metallic reflections (Fig. 9A); metatarsomere 2 with tarsal pad more than 0.6 times as long as ventral length of tarsomere (Fig. 7A); pits near middle annuli of ovipositor less than 0.5 times as high as lancet height in lateral view (Fig. 10A)	S. chimera Ge, sp. nov.
6’	Abdomen shiny black without distinct metallic reflections (Fig. 17); metatarsomere 2 with tarsal pad less than 0.5 times as long as ventral length of tarsomere; pits near middle annuli of ovipositor at least 0.5 times as high as lancet height in lateral view (Fig. 10G)	S. piceus Xiao & Wu, 1983
7’	Fore and middle femora and tibiae largely reddish brown	S. tianshanicus (Semenov, 1921)
7	Fore and middle femora and tibiae largely bright yellowish	S. dux (Semenov, 1921)

3.2.2. Key to males

1	Basal flagellar segments of antennae bright yellowish (Fig. 3F–H)	2
1’	Basal flagellar segments of antennae brownish or blackish (Figs 3, 4)	3
2	Hind femur largely blackish, with a yellowish spot apically; metatibia more than 4.0 times as long as its maximum width (Fig. 8C)	S. ermak (Semenov, 1921)
2’	Hind femur completely yellowish; metatibia less than 4.0 times as long as its maximum width (Fig. 8D)	S. juvencus (Linnaeus, 1758)
3	Abdomen distinctly bicolored, basal blackish segments with dark metallic reflections strongly contrast to middle bright yellowish parts (Fig. 9)	4
3’	Abdomen completely darkish, basal blackish segments weakly contrast to apical dark reddish-brown parts (Fig. 15E)	S. nitobei Matsumura, 1912 dark form
4	Hind femur completely blackish (Fig. 11D)	5
4’	Hind femur largely yellowish	6
5	Abdominal segment IV yellowish (Figs 9B, 11C), metatibia at least 4.0 times as long as its maximum width (Fig. 8A)	S. chimera Ge, sp. nov.
5’	Abdominal segment IV darkish (Figs 9D, 12C), metatibia less than 4.0 times as long as its maximum width (Fig. 8B)	S. dux (Semenov, 1921)
6	Abdominal segment IX yellowish (Fig. 9M), metatibia at least 4.2 times as long as its maximum width (Fig. 8E)	S. nitobei Matsumura, 1912 red form
6’	Abdominal segment IX blackish (Fig. 9L), metatibia less than 4.2 times as long as its maximum width (Fig. 8)	7
7	Abdominal segment III yellowish and VIII blackish (Fig. 9O); metatibia at least 3.7 times as long as its maximum width (Fig. 8F)	S. noctilio Fabricius, 1793
7’	Abdominal segment III blackish, and VIII yellowish (Fig. 18E); metatibia less than 3.6 times as long as its maximum width (Fig. 8)	S. tianshanicus (Semenov, 1921)

Figure 3.

Antennae of Sirex species distributed in China.

Figure 4.

Head (frontal view) of Sirex species distributed in China.

Figure 5.

Head (dorsal view) of Sirex species distributed in China.

3.3. Taxonomic revision of the Sirex species in China

3.3.1. Genus Sirex Linnaeus

Sirex Linnaeus, 1760 [1761]: 396. Type species: Sirex juvencus Linnaeus designated by Curtis (1829: plate 253).

Sirex subg. Paururus Konow, 1896: 41, 43. Type species: Sirex juvencus Linnaeus designated by Rohwer, 1911. Objective synonymy by Bradley (1913: 9).

Diagnosis.

Both sexes with vein Cu1 present on forewing; body always with blue, purple or greenish metallic reflections on dark areas; genae without ridge behind eye, without a white spot dorsally. Females with cornus in dorsal view not constricted near the middle.

3.3.2. Sirex chimera Ge, sp. nov.

https://zoobank.org/478D9409-CC69-40C7-B415-3E366E174DE5

Figure 11

Material examined.

Type specimens: 1♀ holotype, 6♀4♂ paratypes, Maojingba National Forest Park, Wangyedian Village, Chifeng, Inner Mongolia, 118.23114800E, 41.60897200N, 2022-VII-5~15, Bai GD leg. Deposited in Beijing Forestry University.

Figure 6.

Head (ventral view) of Sirex species distributed in China.

Figure 7.

Hind tarsus of females of Sirex species distributed in China.

Figure 8.

Hind tibia and tarsus of males of Sirex species distributed in China.

Figure 9.

Abdomen of Sirex species distributed in China.

Figure 10.

Ovipositor of Sirex species distributed in China.

Figure 11.

Sirex chimera Ge, sp. nov. A Holotype ♀, dorsal view. B Paratype ♀, lateral view. C Paratype ♂, dorsal view. D Paratype ♂, lateral view.

Etymology.

This specific epithet alludes to the Greek mythological monster Chimera which combined a lion’s head, a goat’s body and a serpent’s tail, denoting the males of the new species resembling S. noctilio and females resembling S. nitobei.

Diagnosis.

Females with wings largely clear (Fig. 11A); vein 3A of forewings absent; antennae and legs largely blackish (Fig. 3A); tarsal pad of metatarsomere 2 0.7–0.8 times as long as ventral length of tarsomere (Fig. 7A). Males with antennae completely dark (Fig. 3B); abdomen segments I–III and VIII–IX largely blackish, IV–VII light yellowish (Fig. 10B); metafemur blackish.

Female Description. Color: Body, legs blackish with dark blue metallic reflections (Fig. 11A, B), terga II–VII sometimes with dark purple metallic reflections medially (Fig. 10A). Antennae and palpi blackish (Fig. 3A). Forewings mainly clear, at most tinted with light brown near outer margin. — Head: Genae with pits less than 4.0 pit diameters apart (Fig. 6A); vertex with pits less than 3.0 pit diameters apart (Fig. 5A), and each pit diameter about 0.3 times as lateral ocelli. — Thorax: Mesoscutum with large pits densely developed in median area, transverse ridges vague. Metatarsomere 2 in lateral view about 2.2–2.5 times as long as height, length about 1.0–1.1 times length of tarsomeres 3+4; tarsal pad 0.7–0.8 times as long as ventral length of tarsomere (Fig. 7A). Forewings vein 3A absent. — Abdomen: Median basin of tergum IX with basal width about 1.2 times as long as median length, maximum width about 1.3–1.5 times as long as median length, median length about 0.55–0.65 times of cornus length. Cornus in dorsal view relatively short, with edges straight to slightly angulate midway; its median length 1.05–1.15 times as long as maximum width of abdomen at junction of terga IX and X. Sheath. Basal section about 1.2 times as long as apical section. Ovipositor. Pits near middle annuli (the area at base of apical section of sheath) 0.27–0.30 times as long as an annulus (Fig. 10A), pits scarcely decreasing in size toward ovipositor base, 0.35–0.41 times as high as lancet height in lateral view, 1.0–1.1 times as long as pits height.

Male Description.

Color: Head, thorax and coxae black with dark blue metallic reflections (Fig. 11C, D). Antennae and hind legs blackish (Fig. 3B), except the base of metatibia and metatarsomere 4 yellowish. Fore and middle legs predominantly yellowish, femora blackish at basal half and reddish brown at apical half, metatarsomeres 5 blackish. Forewings tinted with light yellowish and slightly pale brownish near outer margin. Abdomen segments I–III and VIII black with dark blue metallic reflections, terga III and VIII partly yellowish, segments IV–VII light yellowish, sternum IX blackish, rarely with yellowish tone at margins (Fig. 9B). — Thorax: Metatibia 4.0–4.3 times as long as maximum width (Fig. 8A). Metatarsomere 1 in lateral view 3.2–3.4 times as long as maximum height.

Distribution.

Only known from the type locality in Inner Mongolia (Chifeng City)

Host.

Larix gmelinii var. principis-rupprechtii (Mayr.)

Note.

All type specimens of the new species were collected during the same year from a single batch of logs at the local forest station. Both male and female individuals were observed emerging from these logs, as confirmed by the collecting researchers and forest station staff. This co-occurrence supports the association between the male and female specimens. Based on the field investigations conducted by the authors, to date the known distributional range of this new species has only been confined to its type locality. Notably, S. nitobei co-occurs with the new species in the same area, demonstrating two sympatric species (Fig. 19). The niche differentiation of these two species is reflected in their different host plants: S. chimera sp. nov. in Larix spp. and S. nitobei in Pinus spp. Phylogenetic analysis suggests that S. nitobei and S. chimera form sister groups, with each of the monophyletic lineage supported by high posterior probabilities (PP=100). The observed K2P genetic distance of 0.07 between these two taxa, coupled with diagnostic morphological differences, provides conclusive evidence for the status of S. chimera sp. nov., given the current status of knowledge for Sirex. Although the current known distribution of S. chimera remains restricted, its preferred coniferous forest habitat is extensively distributed across northern China.

3.3.3. Sirex dux (Semenov, 1921), stat. rev. (New record from China.)

Figure 12

Paururus dux Semenov, 1921, Russkoe Entomologicheskoe obozrenie, 17 [1917]: 90–91. (original description)

Sirex dux Semenov: Benson, 1943, Bulletin of Entomological Research, 34: 38. (keyed)

Sirex cyaneus dux Semenov: Benson, 1965, The Annals and Magazine of Natural History, series 13, 8 (87): 141. (treated as subspecies of S. cyaneus)

Material examined.

Type specimens: 1♀ holotype, “Abast” (in Russian) – Abastumani (Georgia, ca. 41°45’22’’N / 42°49’41’’E) VIII-17 (year not indicated), deposited in Museum St. Petersburg. Additional specimens: 8♀1♂ Banfanggou Valley, Urumqi, Xinjiang, 2016-VIII-5, Gao T and Lu ZB leg.; 7♀ Daifuseng Village, Wusu, Xinjiang, 2016-VII-3, Gao T and Lu ZB leg.; 3♀ Wulasitai Village, Wusu, Xinjiang, 2016-VII-27, Gao T and Lu ZB leg.; 4♀ Tiereketi Village, Habahe County, Xinjiang, 2017-VIII-5, 1035m, Gao T and Lu ZB leg.; 22♀ Haxionggou Valley, Miquan, Xinjiang, 2016-VIII-18, Gao T and Lu ZB leg.; 11♀ Jibuku Village, Qitai County, Xinjiang, 2016-VII-14, Gao T leg.; 2♀ Jiadengyu National Forest Park, Altai, Xinjiang, 2017-VII-27, 1418m, Gao T and Lu ZB leg.

Diagnosis.

Females with wings largely clear (Fig. 12A, F); vein 3A of forewings absent; antennae completely blackish; legs largely bright yellowish (except coxae blackish); tarsal pad of metatarsomere 2 about 0.8 times as long as ventral length of tarsomere (Fig. 7B).

Female Description.

Color: Head and thorax blackish with dark blue metallic reflections (Fig. 12A, E). Antennae and palpi dark brownish to blackish (Fig. 3C). Legs yellowish (except coxae black with dark blue metallic reflections). Forewings almost clear. Abdomen blackish with dark purple metallic reflections (Fig. 9C). — Head: Genae with pits 0.3–5.6 pit diameters apart (Fig. 6C); vertex with pits less than 5.0 pit diameters apart, and each pit diameter about 0.12–0.23 times as lateral ocelli (Fig. 5C). — Thorax: Mesoscutum with large pits densely developed in median area, with transverse and longitudinal ridges in coarsely pitted area. Metatarsomere 2 in lateral view about 2.2–2.3 times as long as height, length about 0.9–1.0 times length of tarsomeres 3+4; tarsal pad about 0.8 times as long as ventral length of tarsomere (Fig. 7B). Forewings vein 3A absent. — Abdomen: Median basin of tergum IX with basal width about 0.8–1.0 times as long as median length, maximum width 1.3–1.5 times as long as median length, median length 0.6–0.8 times of cornus length. Cornus in dorsal view short, with edges straight, its median length 0.9–1.1 times as long as maximum width of abdomen at junction of terga IX and X. Sheath. Basal section 1.05–1.15 times as long as apical section. Ovipositor. Pits near middle annuli (the area at base of apical section of sheath) 0.13–0.18 times as long as an annulus (Fig. 10B), pits moderately decreasing in size toward ovipositor base, 0.18–0.30 times as high as lancet height in lateral view, 1.08–1.60 times as long as pit height.

Male Description.

Color: Head, thorax, and coxae black with dark blue metallic reflections (Fig. 12C, D). Antennae and hind legs blackish (Fig. 3D). Fore and middle legs with tarsus yellowish, femora and tibiae dark yellowish brown. Forewings tinted light yellowish. Abdomen segments I–IV, VIII and sternum IX black with dark blue or purple metallic reflections, segments V–VII largely light yellowish with apical part of each segment darkish with purple metallic reflections (Fig. 9D). — Thorax: Metatibia 3.6 times as long as maximum width (Fig. 8B). Metatarsomere 1 in lateral view 2.9 times as long as maximum height.

Figure 12.

Sirex dux (Semenov, 1921). A ♀, dorsal view. B ♀, lateral view. C ♂, dorsal view. D ♂, lateral view. E Holotype ♀, dorsal view. F Holotype ♀, lateral view. G Original collection label of holotype.

Distribution.

Gansu (Zhangye City; Wuwei City; Baiyin City), Ningxia (Helan Mountains), Qinghai (Menyuan County), Xinjiang (Urumqi; Shihezi City; Yili City; Tacheng City; Altay Prefecture; Changji Prefecture).

Host.

Picea obovata Ledeb.; P. schrenkiana Fisch. & C.A.Mey (Fig. 19).

Note.

Females of this species can be easily distinguished from other Chinese Sirex species (excluding S. tianshanicus) by their entirely black antennae and predominantly yellowish legs. Although initially collected during field surveys conducted several years ago and known to exhibit a broad distribution across western China, no formal records of this taxon were published prior to this study. Notably, this study is also the first formal description of the male of the species, even though only one specimen was obtained through several years’ fieldwork. This taxon historically classified as a subspecies of S. cyaneus, our phylogenetic analysis suggests that S. dux and S. nitidus form a monophyletic group, which is sister to S. cyaneus. Based on the molecular findings and consistent morphological differentiation, we propose reinstating S. dux stat. rev. as a distinct species.

3.3.4. Sirex ermak (Semenov, 1921)

Figure 13

Paururus ermak Semenov, 1921, Russkoe Entomologicheskoe obozrenie, 17 [1917]: 92. (original description)

Sirex ermak Semenov: Benson, 1943, Bulletin of Entomological Research 34: 30–32. (listed)

Sirex ermak Semenov: Xiao et al., 1992, Economic Sawfly Fauna of China: 38–42. (described, figured, keyed)

Sirex ermak Semenov: Xiao & Wu, 1983, Memoir of Forest Entomology: 2–5. (described, figured, keyed)

Material examined.

4♀ Kadelate Village, Fuyun Country, Altai, Xinjiang, 2023-VIII-31, Ren L leg.; 6♀4♂ Kadelate Village, Fuyun Country, Altai, Xinjiang, 2024-VII-28~30, Ren L leg.; 4♀ Tiereketi Village, Habahe County, Xinjiang, 2017-VIII-5, 1035m, Gao T and Lu ZB leg.

Diagnosis.

Females with forewings more or less darkened at least in the middle part (Fig. 13A, B); vein 3A of forewings basally present (Fig. 13B); antennae completely blackish (Fig. 3E); legs largely darkish; tarsal pad of metatarsomere 2 about 0.8 times as long as ventral length of tarsomere (Fig. 7C). Males with flagellar basally yellowish (Fig. 3F); abdomen segments I–III and VII–IX blackish, IV–VI light yellowish (Fig. 9F). Metafemur largely blackish with a yellowish spot developed apically (Fig. 13E).

Figure 13.

Sirex ermak (Semenov, 1921). A ♀, dorsal view. B Forewing of female. C ♀, lateral view. D ♂, dorsal view. E ♂, lateral view.

Female Description.

Color: Head and thorax blackish with dark blue metallic reflections (Fig. 13A, C). Antennae and palpi dark brownish to blackish (Fig. 3E). Legs with coxae and femora black with dark blue metallic reflections, tibiae and tarsi dark brownish. Forewings with basal half almost clear and apical half pale brownish hue, sometimes with brownish moderately deepening before pterostigma, thus forms vague brownish bands (Fig. 13B). Abdomen blackish with terga I and IX dark bluish metallic reflections while terga II–VIII dark purple metallic reflections in dorsal view (Fig. 9E). — Head: Genae with pits 0.7–3.0 pit diameters apart (Fig. 6E), vertex and postocellar area with pits less than 3.5 pit diameters apart (Fig. 5E), and each pit diameter about 0.2–0.5 times as lateral ocelli. — Thorax: Mesoscutum with coarse net-like pits on median area, with indistinct transverse and longitudinal ridges in coarsely pitted area. Metatarsomere 2 in lateral view about 2.3–2.5 times as long as height, length about 1.15–1.25 times length of tarsomeres 3+4; tarsal pad about 0.8 times as long as ventral length of tarsomere (Fig. 7C). Forewings vein 3A basally present (Fig. 13B). — Abdomen: Median basin of tergum IX with basal width 0.8–0.9 times as long as median length, maximum width 1.1–1.2 times as long as median length, median length 0.8–0.9 times of cornus length. Cornus in dorsal view short, with edges straight and angulate midway, its median length 1.0–1.2 times as long as maximum width of abdomen at junction of terga IX and X. Sheath. Basal section 1.04–1.10 times as long as apical section. Ovipositor. Pits near middle of annuli (the area at base of apical section of sheath) 0.06–0.1 times as long as annulus (Fig. 10C), pits moderately decreasing in size toward ovipositor base, about 0.37 times as high as lancet height in lateral view, 0.5–0.6 times as long as pits height.

Male Description.

Color: Head, thorax and coxae black with dark blue metallic reflections (Fig. 13D, E). Antennae with scape and pedicel blackish, flagella basally yellowish from flagellomere 1 to flagellomere 3–5, distal part of flagellar darkish (Fig. 3F). Fore and mid legs with femora blackish (sometimes fore femora grades to brownish-yellow apically), tibiae and tarsi yellowish. Hind legs mostly blackish except a yellowish spot on the apical part of femora and metatarsomeres 4–5 yellowish. Forewings tinted light yellow and slightly pale brownish near outer margin. Abdomen with segments I–III and VII–IX black with dark blue metallic reflections, segments IV–VI light yellowish (Fig. 9F). — Thorax: Metatibia about 4.1–4.2 times as long as maximum width (Fig. 8C). Metatarsomere 1 in lateral view 3.3 times as long as maximum height.

Distribution.

Qinghai (Huzhu County, Banma County); Xinjiang (Fuyun County, Buerjin County).

Host.

Picea obovata; Larix sp.

Note.

A species distributed in both eastern and western China but not recorded in central China (Fig. 19). This species is similar to S. nitobei but can be distinguished from all Chinese Sirex based on the basally presence of vein 3A.

3.3.4. Sirex juvencus (Linnaeus, 1758)

Figure 14

Ichneumon Juvencus [sic!] Linnaeus, 1758; Systema Naturae (1): 560. (original description)

Sirex juvencus ab. pallescens Linnaeus: Stroganova, 1973, Novye i maloizvestnye vidy fauny Sibiri (6): 73–75 (Not available. Infrasubspecific name.)

Sirex juvencus ab. ermakianum Linnaeus: Stroganova, 1973, Novye i maloizvestnye vidy fauny Sibiri (6): 73–75 (Not available. Infrasubspecific name.)

Sirex juvencus ab. noctiliolum Linnaeus: Stroganova, 1973, Novye i maloizvestnye vidy fauny Sibiri (6): 73–75 (Not available. Infrasubspecific name.)

Sirex juvencus forma tipica Linnaeus: Stroganova, 1973, Novye i maloizvestnye vidy fauny Sibiri (6): 73–75 (Not available. Infrasubspecific name.)

Material examined.

5♀10♂ Kadelate Village, Fuyun Country, Altai, Xinjiang, 2024-VII-28~30, Ren L leg.; 24♀ Tiereketi Village, Habahe County, Xinjiang, 2017-VIII-5, 1035m, Gao T and Lu ZB leg.; 13♀ Jiadengyu National Forest Park, Altai, Xinjiang, 2017-VII-27, 1418m, Gao T and Lu ZB leg.

Diagnosis.

Females with apical half of forewings tinted pale brownish (Fig. 14A); vein 3A of forewings absent; antennae with flagellar basally bright yellowish (Fig. 3G); legs largely bright yellowish (except coxae blackish); tarsal pad of metatarsomere 2 about 0.7 times as long as ventral length of tarsomere (Fig. 7D). Male antennae with flagellar basally bright yellowish (Fig. 3H); hind femora bright yellowish.

Female Description.

Color: Head, thorax, coxae and abdomen black with dark blue metallic reflections (abdomen with segments II–VIII dark purple metallic reflections) (Fig. 14A). Antennae with basal half yellowish (except for scape dark brownish to brownish) while gradient to blackish towards the apical half (Fig. 3G). Femora brownish; tibiae and tarsi yellowish (sometimes with tarsomeres 5 brownish). Forewings with basal half clear and tinted pale brownish on apical half, brownish spot around cell 1R1 weakly developed. — Head: Genae with pits 0.1–5.0 pit diameters apart (Fig. 6G); vertex with pits less than 3.0 pit diameters apart, and each pit diameter 0.11–0.32 times as lateral ocelli (Fig. 5G). — Thorax: Mesoscutum with coarse, net-like pits in median area, transverse or longitudinal ridge indistinct or absent. Metatarsomere 2 in lateral view 2.0–2.5 times as long as height, length about 1.1–1.3 times length of tarsomeres 3+4; tarsal pad about 0.7 times as long as ventral length of tarsomere (Fig. 7D). Forewings vein 3A absent. — Abdomen: Median basin of tergum IX with basal width 0.8–0.9 times as long as median length, maximum width 1.0–1.2 times as long as median length, median length 0.7–0.8 times of cornus length. Cornus in dorsal view long and thick, with edges straight and curved apically, clearly angled at about 1/6 of the basal junction, its median length 1.2–1.3 as long as maximum width of abdomen at junction of terga IX and X. Sheath. Basal section 1.0–1.1 times as long as apical section. Ovipositor. Pits near middle annuli (the area at base of apical section of sheath) 0.25–0.30 times as long as an annulus, pits not decreasing in size toward base (Fig. 10D), 0.4–0.5 times as high as lancet height in lateral view, 0.9–1.0 times as long as pits height.

Male Description.

Color: Head, thorax and coxae black with dark blue metallic reflections (Fig. 14C). Antennae with basal half bright yellowish while blackish in the apical half (Fig. 3H). Fore and mid legs bright yellowish from femora to tarsi. Hind legs mostly blackish except femora bright yellowish. Forewings tinted light yellow and slightly pale brownish near outer margin. Abdomen with segments I–II blackish with dark blue metallic reflections; segments V–VIII light yellowish; segments III–IV and IX largely yellowish with more or less darkish tone (Fig. 9H). — Thorax: Metatibia about 3.9–4.0 times as long as maximum width (Fig. 8D). Metatarsomere 1 in lateral view 3.5 times as long as maximum height.

Distribution.

Heilongjiang; Jilin; Inner Mongolia; Shanxi; Gansu; Qinghai; Xinjiang.

Host.

Picea sp. (e.g. P. crassifolia Kom.; P. obovata Ledeb.; P. schrenkiana Fisch. & C.A.Mey.), P. sylvestris var. mongholica Litv.

Note.

This species is widespread in northern China. Its females can be easily identified by the yellowish color in the basal half of antennae.

3.3.5. Sirex nitobei Matsumura, 1912

Figure 15

Sirex nitobei Matsumura, 1912, Thousand insects of Japan. Supplement IV: 17–18. (original description)

Sirex nitobei Matsumura: Xiao et al., 1992, Economic Sawfly Fauna of China: 38–42. (described, keyed)

Sirex nitobei Matsumura: Xiao & Wu, 1983, Memoir of Forest Entomology: 2–5. (described, keyed)

Sirex rufiabdominis Xiao & Wu, 1983, Memoir of Forest Entomology: 2–5. syn. nov.

Sirex sinicus Maa, 1949, Notes d’Entomologie Chinoise, 13(2): 124–126. syn. nov.

Sirex imperialis W.F. Kirby: Xiao & Wu, 1983, Memoir of Forest Entomology: 2–5. (original record) [misidentification]

Material examined.

Type specimens: 1♀ holotype of Sirex rufiabdominis Xiao & Wu, 1983, Fuyang District, Hangzhou, Zhejiang, 1986-X-7, deposited in Chinese Academy of Forestry; 1♂ paratype of Sirex rufiabdominis Xiao & Wu, 1983, “Yangxian” probably Chuzhou City (due to illegible handwriting, the exact characters cannot be identified), Anhui, 1981 (month and date not indicated), deposited in Chinese Academy of Forestry. Additional specimens: 1♂ Mt. Jiulong, Mentougou District, Beijing, 2015-XII-25 (emerged), Gao T leg.; 2♀7♂ Chifeng City, Inner Mongolia, Gao T leg.; 10♀13♂ Fei County, Linyi, Shandong, 2019-IX, Xu Q leg.

Figure 14.

Sirex juvencus (Linnaeus, 1758). A ♀, dorsal view. B ♀, lateral view. C ♂, dorsal view. D ♂, lateral view.

Diagnosis.

Females with apical half of forewings moderately to strongly darkened (Fig. 15A–D); vein 3A of forewings absent; antennae completely blackish (Fig. 3I); tarsal pad of metatarsomere 2 0.7–0.8 times as long as ventral length of tarsomere (Fig. 7E). Males with flagellar basally brownish to dark brownish (Fig. 3J); abdomen segments completely darkish or I–II blackish, III–IX yellowish (Fig. 9L, M).

Female Description.

Color: With different color forms. Head, Antennae and thorax blackish with dark blue metallic reflections. In dark forms, legs blackish with more or less dark blue metallic reflections (Fig. 15A). In red forms, color of legs variable, coxae and femora blackish with dark blue or purple metallic reflections, while tibiae and tarsi from dark brownish to completely light reddish brown (variable based on individuals) (Fig. 15B, C, H). Forewings with basal half clear and apical half brownish to dark brownish (in red form comparatively light but darkened in dark forms), brownish area moderately deepening before pterostigma, sometimes forms vague brownish bands. Dark forms with abdomen completely blackish, terga I and IX always dark blueish metallic reflections while terga II–VIII dark purple metallic reflections in dorsal view (Fig. 9I). Red forms with color of abdomen variable, terga I and IX always dark blueish metallic reflections while terga II–VIII from more or less reddish brown to completely light reddish brown (Fig. 9J, K). — Head: Genae with pits 0.1–2.5 pit diameters apart (Fig. 6I), vertex and postocellar area with pits less than 2.0 pit diameters apart, and each pit diameter about 0.1–0.25 times as lateral ocelli (Fig. 5I). — Thorax: Mesoscutum widely covered with net-like pits in median area. Metatarsomere 2 in lateral view 1.7–2.0 times as long as height, length about 0.9–1.1 times length of tarsomeres 3+4; tarsal pad 0.7–0.8 times as long as ventral length of tarsomere (Fig. 7E). Forewings vein 3A absent. — Abdomen: Median basin of tergum IX with basal width about 0.8–1.1 times as long as median length (always less than 1.0 times in red forms, while more than 1.0 times in intermediate and dark forms), maximum width 0.9–1.3 times as long as median length (always less than 1.0 times in red forms, while about 1.2 times in intermediate and dark forms), median length 0.8–1.1 times of cornus length. Cornus in dorsal view rather short, with edges in the basal half straight and curved apically, distinctly angulate midway, its median length 0.7–0.9 times as long as maximum width of abdomen at junction of terga IX and X. Sheath. Basal section 1.1–1.3 times as long as apical section. Ovipositor. Pits near middle annuli (the area at base of apical section of sheath) 0.27–0.33 times as long as an annulus, pits not decreasing in size toward ovipositor base (Fig. 10E), about 0.4 times as high as lancet height in lateral view, 0.7–0.9 times as long as pits height.

Figure 15.

Sirex nitobei Matsumura, 1912. A Dark form ♀, dorsal view. B Intermediate form ♀, dorsal view. C Red form ♀, dorsal view. D Dark form ♀, lateral view. E Dark form ♂, dorsal view. F Red form ♂, dorsal view. G Red form ♂, lateral view. H Holotype ♀ of Sirex rufiabdominis Xiao & Wu, 1983. I Original collection label of holotype ♀ of Sirex rufiabdominis Xiao & Wu, 1983. J Paratype ♂ of Sirex rufiabdominis Xiao & Wu, 1983. K Original collection label of paratype ♂ of Sirex rufiabdominis Xiao & Wu, 1983.

Male Description.

Color: With different color forms. Head, thorax and coxae blackish with dark blue metallic reflections. Antennae with basal half dark brownish to brownish (except for scape blackish) and apical half blackish (Fig. 3J). Fore and middle legs brownish to yellowish brown (except coxae black). Hind legs with femora yellowish brown (in dark forms dark brownish) (Fig. 15E–G); metatibiae blackish. In dark forms with metatarsomere 1–3 and 5 blackish while metatarsomere 4 brownish in dorsal view; in red forms with metatarsomere 1–3 blackish while metatarsomere 4+5 yellowish brown. Fore and hindwings yellowish. Abdomen with segments I–II blackish with dark blue or purple metallic reflections; in dark forms with terga III–VIII (including sternum IX) dark brownish (Fig. 9L), while light yellowish brown in red forms (Fig. 9M). — Thorax: Metatibia 4.2–4.9 times as long as maximum width (Fig. 8E). Metatarsomere 1 in lateral view 2.7–3.1 times as long as maximum height.

Distribution.

Almost nationwide: Heilongjiang; Jilin; Liaoning; Inner Mongolia; Beijing; Hebei; Henan; Shandong; Shaanxi; Anhui; Jiangsu; Zhejiang; Gansu; Yunnan; Xinjiang.

Host.

Pinus sp. (e.g. P. tabuliformis Carr.; P. sylvestris var. mongholica Litv.; P. thunbergii Parl.; P. massoniana Lamb.)

Note.

This species is the most widespread Sirex species in China. Earlier studies mistakenly classified different color variants of it as distinct species (i.e. S. rufiabdominis Xiao & Wu) because their appearance varies greatly. After studying series of specimens (including type series of S. rufiabdominis Xiao & Wu), we discovered that these color variants are merely individually and continuously with no structural differences. Molecular phylogenetic analysis also confirms that they belong to the same species. Therefore, based on both morphological characters and molecular data, we propose S. rufiabdominis Xiao & Wu as a junior synonym of S. nitobei Matsumura, i.e. S. rufiabdominis Xiao & Wu, 1983 syn. nov. Another confusing case is S. sinicus Maa, which was named based on single male holotype from Beijing, where S. nitobei also occurs. By comparing the original description (Maa, 1949) with our examined specimens (the type specimen of S. sinicus has not been examined), we found no significant differences between S. sinicus and S. nitobei. We propose S. sinicus Maa as a junior synonym of S. nitobei Matsumura, i.e. S. sinicus Maa, 1949 syn. nov. Additionally, Xiao and Wu (1983) reported S. imperialis W.F. Kirby, 1882 in China based on specimens deposited in the Chinese Academy of Forestry. Our rechecking of these specimens also identifies them as S. nitobei, confirming that S. imperialis does not occur in China.

3.3.6. Sirex noctilio Fabricius, 1793

Figure 16

Sirex noctilio Fabricius, 1793, Entomologica systematica emendata et aucta. Vol. 2: 104–132. (original description)

Sirex melanocerus Thomson, 1871, Hymenoptera Scandinaviae. 1: 328.

Paururus atlantidis Ghigi, 1909, Sopra una nuova specie di Siricide delle Azore. 40 [1908] (3–4): 163–170.

Material examined.

2♀4♂ Dorbod County, Daqing, Heilongjiang, 2016-VI-30, Gao T leg.; Hekuangjunde Forest Farm, Hegang, Heilongjiang, 2013-VII-25~26, Wang H leg.; 4♀ Bamiantong Town, Mudanjiang, Heilongjiang, 2015-VIII-14, Wang ZG leg.; 3♂ Yushu, Jilin, Sun XT leg.; 3♀ Kangping, Shenyang, Liaoning, 2016-VI-25, Gao T leg.; 3♀ Zhanggutai Town, Fuxin, Liaoning, 2016-VI-25, Gao T leg.; 3♀4♂ Chengjiao Forest Farm, Chifeng City, Inner Mongolia, 2016-V-23, Gao T leg.

Diagnosis.

Females with brownish spot around cell 1R1 (Fig. 16A); vein 3A of forewings absent; antennae completely blackish (Fig. 3K); legs largely yellowish (except coxae blackish); tarsal pad of metatarsomere 2 0.3–0.4 times as long as ventral length of tarsomere (Fig. 7F). Males with antennae completely darkish (Fig. 3L); abdomen segments I–II and VIII–IX blackish, III–VII yellowish (Fig. 9O); hind femora reddish brown.

Female Description.

Color: Body, antennae and palpi black with dark blue or purple metallic reflections (Fig. 16A). Coxae and apical tarsomeres blackish; femora (except basal part brownish), tibiae and tarsi light yellowish brown (In black forms with metafemur blackish). Forewings mostly clear but with brownish spot around cell 1R1. — Head: Genae with small pits about 3.0–9.0 pit diameters apart (Fig. 6K), vertex and postocellar area with pits 1.0–8.0 pit diameters apart, each pit diameter about 0.1–0.2 times as lateral ocelli (Fig. 5K). — Thorax: Mesoscutum with large and shallowly pits in median area, pits more or less tooth-like process behind and teeth rarely fused transversally, thus without distinct transverse ridges. Metatarsomere 2 in lateral view 2.9–3.5 times as long as height, length about 1.1–1.4 times tarsomeres 3+4; tarsal pad 0.3–0.4 times as long as ventral length of tarsomere (Fig. 7F). Forewings vein 3A absent. — Abdomen: Median basin of tergum IX with basal width 0.9–1.1 times as long as median length, maximum width about 1.1–1.3 times as long as median length, median length 0.5–0.7 times of cornus length. Cornus in dorsal view short, with edges in the basal half straight and slightly curved apically, its median length about 1.0–1.2 times as long as maximum width of abdomen at junction of terga IX and X. Sheath. Basal part about 1.0–1.3 times as long as length of apical section. Ovipositor. Pits near middle annuli (the area at base of apical section of sheath) 0.50–0.75 times as long as an annulus, pits slightly decreasing in size toward base (Fig. 10F), 0.6–0.8 times as high as lancet height in lateral view, 1.4–2.0 times as long as pits height.

Male Description.

Color: Head, thorax, antenna and coxae black with dark blue metallic reflections (Fig. 16C, D). For and middle legs with femora (except for basal part brown), tibiae and tarsi light yellowish brown; metatibia and metatarsus blackish (except metatarsomere 4 and basal part of metatarsomere 5 yellowish brown); basal part of metatibia with yellowish brown area about 2.0–3.0 times as long as minimum width of tibia (Fig. 8F). Forewings light yellowish, with pale brownish hue slightly developed near outer margin. Abdomen with terga I–II and VIII (including sternum IX) blackish, while III–VII light yellowish brown (sometimes color of tergum III can be variable, from black with dark purple metallic reflections to yellowish brown) (Fig. 9O). — Thorax: Metatibia 3.8–4.2 times as long as maximum width (Fig. 8F). Metatarsomere 1 in lateral view 2.7–3.8 times as long as maximum height.

Distribution.

Mainly distributed in Northeast China: Heilongjiang; Jilin; Liaoning; Inner Mongolia.

Host.

P. sylvestris var. mongolica Litv.

Note.

Schiff et al. (2012) conducted a detailed discussion on the morphology, biology, and related taxonomic treatments of this species. Intriguingly, these authors also highlighted the presence of the black form. According to Schiff et al. (2012), the black form seems be rare and could be found in southern Europe only, and there are no intermediate color forms between the black form and other specimens of S. noctilio. In China, we have not yet collected the black form of males, but the black form of females was discovered with a very low proportion to the typical forms of approximately 1/1000.

Figure 16.

Sirex noctilio Fabricius, 1793. A ♀, dorsal view. B ♀, lateral view. C ♂, dorsal view. D ♂, lateral view.

3.3.7. Sirex piceus Xiao & Wu, 1983

Figure 17

Sirex piceus Xiao & Wu, 1983, Memoir of Forest Entomology, (2): 4–5. (original description)

Material examined.

Type specimen: 1♀ holotype, deposited in Chinese Academy of Forestry.

Diagnosis.

Females with wings largely clear (Fig. 17A); vein 3A of forewings absent; antennae completely blackish; legs largely blackish; thorax and abdomen shiny blackish; tarsal pad of metatarsomere 2 about 0.45 times as long as ventral length of tarsomere.

Female Description.

Color: Head, thorax and abdomen shiny blackish (Fig. 17A, B). Antennae and palpi dark brownish to blackish. Legs blackish to dark brownish. Wings clear, with apex and outer margin slightly brownish hue. Veins dark brownish to blackish, pterostigma black. — Head: Genae with pits less than 2.0 pit diameters apart; vertex with pits less than 4.0 pit diameters apart. — Thorax: Mesoscutum with large pits densely developed in median area, more or less reticulate patterns in coarsely pitted area. Metatarsomere 2 with its length 0.88 times length of tarsomeres 3+4; tarsal pad 0.45 times as long as ventral length of tarsomere. Fore wing vein 3A absent. — Abdomen: Median basin of tergum IX without longitudinal ridge, basal width about 0.7 times as long as median length, maximum width about 1.0 times as long as median length, median length 0.65 times cornus length. Cornus in dorsal view long, triangular shaped without distinct angulate midway, its median length 2 times as long as maximum width of abdomen at junction of terga IX and X. Sheath. Basal section 1.14 times as long as apical section. Ovipositor. Pits near middle annuli (the area at base of apical section of sheath) about 0.3 times as long as an annulus, 0.54 times as high as lancet height in lateral view, 0.85 times as long as pits height (Fig. 10G).

Distribution.

Qinghai (Maqin County). Only recorded from the type locality.

Host.

Picea sp. (Original label data).

Note.

According to the original description, this species was described on a single female holotype. In subsequent studies, no new specimens were collected or described. Although the original literature described that “body blue-black, with metallic reflections”, according to the examined holotype, the specimen (compared to other Sirex females with bluish metallic reflections) is much darker, with the blue reflections only be observed vaguely in lateral view. Since no more specimens have been studied, it is difficult to determine whether this character is stable.

3.3.8. Sirex tianshanicus (Semenov, 1921)

Figure 18

Paururus tianshanicus Semenov, 1921, Russkoe Entomologicheskoe obozrenie, 17[1917]: 91–92. (original description)

Sirex tianshanicus (Semenov): Xiao and Wu 1983, Memoir of Forest Entomology: 2–5. (original record)

Material examined.

Type specimen: 1♀ holotype, Issyk-kul near Przhewalsk, 1918-VIII-05, Ya. Korolkov leg., deposited in Museum St. Petersburg. Additional specimens: 1♀, Laomancheng, Urumqi, Xinjiang, 1981-V-24, Fan Yong & Li Hui leg., deposited in Chinese Academy of Forestry. 1♂, Kunlun Mountains, Qiemo County, Xinjiang, 1984-VII-12, deposited in Chinese Academy of Forestry.

Diagnosis.

Females with wings largely clear (Fig. 18A, D); vein 3A of forewings absent; antennae completely blackish; legs largely bright yellowish (except coxae blackish); Males antennae completely darkish; abdomen with segments I–III and IX darkish, IV–VIII yellowish brown; hind femora bright reddish brown.

Figure 17.

Sirex piceus Xiao & Wu, 1983. A Holotype ♀, dorsal view. B Holotype ♀, lateral view and original collection label of holotype.

Female Description.

Color: Head and thorax blackish with dark blue metallic reflections. Antennae and palpi dark brownish to blackish. Legs brownish to yellowish (except coxae black with dark blue metallic reflections). Forewings almost clear. Abdomen blackish with dark purple metallic reflections. — Head: Genae with pits less than 5.4 pit diameters apart; vertex with pits less than 6.6 pit diameters apart, and each pit diameter about 0. 25–0.46 times as lateral ocelli. — Thorax: Mesoscutum with large pits densely developed in median area, more or less reticulate patterns in coarsely pitted area. Metatarsomere 2 with its length 0.84 times length of tarsomeres 3+4. Fore wing vein 3A absent. — Abdomen: Median basin of tergum IX with distinct median longitudinal ridge, basal width about 0.75–0.82 times as long as median length, maximum width 1.0–1.1 times as long as median length, median length 0.7–0.8 times of cornus length. Cornus in dorsal view short, its median length 1.5–1.7 times as long as maximum width of abdomen at junction of terga IX and X. Sheath. Basal section 1.14 times as long as apical section. Ovipositor. Not examined.

Male Description.

Color: Head, thorax and coxae black with dark blue or greenish metallic reflections. Antennae dark brownish to blackish. Fore and middle legs reddish brown from femora to tarsi. Hind legs mostly blackish except femora bright reddish brown. Forewings tinted light yellow and slightly pale brownish near outer margin. Abdomen with segments I–III and IX darkish; segments IV–VIII yellowish brown. — Thorax: Metatibia about 3.1 times as long as maximum width. Metatarsomere 1 in lateral view 3.3 times as long as maximum height.

Distribution.

Xinjiang (near Urumqi, Qiemo County); South Gansu (near Zhuoni County)

Host.

Picea schrenkiana Fisch. & C.A.Mey.

Note.

Our recent field surveys failed to collect this species in Xinjiang, even near its originally reported sites (Xiao and Wu 1983). This absence could suggest local habitat alterations or undetected ecological requirements. Specimens determined as this species by Xiao are deposited in the collection of the Chinese Academy of Forestry, but their collection date was 1984 (postdating to the original records). This raises questions about their connection to the initial discovery. The ovipositor was not exposed in either of the examined female specimens, preventing examination of this structure.

Figure 18.

Sirex tianshanicus (Semenov, 1921). A Holotype ♀, dorsal view. B Holotype ♀, lateral view. C Original collection label of holotype. D ♀, dorsal view. E ♂, lateral view.

Females of this taxon show striking morphological similarity to S. dux, with which it has a substantial range overlap. However, the males of the two species exhibit notable morphological differences (e.g. yellowish hind femur in S. tianshanicus while darkish in S. dux). Detailed comparisons revealed that there are no consistent differences for the standard diagnostic features between the females. A potential distinguishing character is the shape of the median basin on tergum IX (flat-elliptical in Chinese S. dux, cushion-shaped in type specimens of S. dux and S. tianshanicus), but it appears variable across populations, diminishing its diagnostic value. Notably, multiple morphological measurements (including ratio-based characteristics) showed overlapping ranges between these two species across studies. Currently, leg coloration (bright yellow in S. dux while reddish brown in S. tianshanicus) serves as the only provisional diagnostic character for the female specimens, as ovipositor comparisons remain unavailable for S. tianshanicus specimens.

Figure 19.

Distribution map of Sirex species distributed in China. Distribution records were synthesized from existing literature documentation, specimen label data from examined material, and original field collections conducted by the authors.

3.3.9. Sirex vates Mocsáry, 1881

Sirex vates Mocsáry, 1881, Természetrajzi Füzetek, 5(1): 36–37.

Material examined.

No material examined, general description of female translated from the original description in Mocsáry, (1881).

General description of female.

Antennae with 21 segments, robust, blackish, covered with dark bristles. Abdomen dark bluish, dorsal segments II–VII completely silky, VIII–IX glossy, covered with sparsely setae; cornus short, conical, basal part completely smooth, apex pointed and rough; ovipositor shorter than abdomen. Legs blackish, tibiae and tarsi of fore and middle legs rust-colored. Wings sub-hyaline with violet sheen; apex slightly smoky, darkened part developed in the basal-middle part, veins black; costa yellowish-brown. Holotype ♀ length 31 mm.

General description of male.

Male unknown.

Distribution.

Sichuan (Guangyuan City) (as in the original description).

Host.

Unknown

Note.

The original publication did not specify type specimen numbers or deposition locations, though the specimens are presumably preserved in Hungarian National Museum, Budapest. This species seems not to have been collected after the original description. According to the description, this species has distinctive characteristics (e.g. a dark brownish band before pterostigma, which might be similar to that of S. nitobei). It is also worth noting that there are conflicting descriptions of the abdominal colors in literature. In Xiao and Wu (1983) and Xiao et al. (1992), it is indicated that abdomen is blackish without metallic reflections. However, the terga II–VII are dull yellowish-brown and terga VII–IX blackish in the description of Quinlyn et al. (2019) (In the original description, abdomen dark bluish, dorsal segments II–VII completely silky, VIII–IX glossy). Existing descriptions of the morphological features align perfectly within the variation range of S. nitobei. This suggests that the species might be merely a synonym of S. nitobei, but this suspicion needs to be confirmed by the examination of the type specimen.

4. Discussion

The wood wasp family Siricidae forms an “early diverging” hymenopteran lineage with a complex taxonomic history. Early studies focused on these insects due to their economic impact and accidental spread through global trade, primarily using simplistic color-based distinctions (e.g., abdominal or leg coloration) for identification (Middlekauff 1960; Smith and Schiff 2002). These characters are not reliable. Later approaches employed ratio-based measurements, including the proportions of basal/apical ovipositor sheath segments and forewing/ovipositor length ratios (Benson 1943), but these features frequently exhibited overlapping ranges between species and sometimes greater intraspecific than interspecific variation.

The taxonomy of Sirex faces persistent challenges due to its history: most taxa were established in the last century with inconsistent diagnostic criteria. Superficial early descriptions make species identification dependent on the examination of type specimens. Additionally, researchers used divergent diagnostic characters: Benson (1943) employed ovipositor/forewing ratios, whereas Xiao and Wu (1983) used ovipositor/abdomen length ratios (excluding the cornus), creating incompatible identification frameworks. Modern revisions by Goulet (2012) and Schiff et al. (2012) developed standardized morphological keys enhanced with DNA barcoding, substantially improving species delineation.

Notably, although mitochondrial COI partial coding sequences often fail to resolve closely related species in certain insect groups (e.g., Pieris and Colias butterflies; Ge et al. 2023), this marker appears to achieve excellent species-level resolution for both Nearctic and Chinese Sirex. This heightened resolution may stem from cyclical parthenogenetic dominance in some species. For instance, our field observations and laboratory rearing data revealed about five dozen of examined S. dux specimens are of females and only a single male specimen has been discovered to date (unpublished data).

However, COI alone provides limited phylogenetic signal for inferring interspecific relationships or higher-level groupings. Consistent with this limitation, our phylogenetic results show relatively low support at some basal nodes. Thus, although COI proves valuable for species delimitation in Sirex, we caution against relying solely on this marker for reconstructing higher level phylogenies, as is well known to be the case.

Phylogenetic analyses reveal notable intraspecific complexity. The Yunnan population of S. nitobei forms a highly supported independent clade, while S. noctilio contains distinct monophyletic lineages, suggesting cryptic speciation. As broad-waisted Hymenoptera, Sirex species exhibit obligate fungal symbiosis, offering a compelling model for co-evolution studies. Integrating phylogenetic and phylogenomic analyses of Sirex and their fungal partners could unravel the molecular mechanisms as well as the evolutionary history behind their specialized ecological adaptations.

5. Declarations

Author Contributions. Sixun Ge: Conceptualization (lead); data curation (lead); formal analysis (lead); methodology (lead); resources (lead); software (lead); visualization (lead); writing original draft (lead). Tai Gao: data curation (equal); resources (equal); visualization (equal); Yizhou Liu: data curation (equal); resources (equal); Jiale Li: data curation (equal); resources (equal); methodology (equal); software (supporting); Juan Shi: resources (supporting); funding acquisition (supporting); project administration (equal); Lili Ren: funding acquisition (equal); project administration (equal); resources (equal); supervision (equal); validation (lead); visualization (equal); writing review and editing (supporting). Hongliang Shi: conceptualization (equal); data curation (equal); resources (equal); methodology (equal); supervision (lead); funding acquisition (supporting); validation (equal); writing review and editing (lead).

Competing interests. The authors declare no competing interests.

Ethics approval and consent to participate. Not applicable.

Consent for publication. Not applicable.

Availability of Data and Materials. All sequences generated in this study were deposited in GenBank (accession numbers are PV290776-PV290840, PV300958-PV300985) Specimens deposited in Beijing Forestry University are available for re-examination by any researcher on request to Si-Xun Ge.

6. Acknowledgments

We gratefully acknowledge Sino-French Joint Laboratory for Invasive Forest Pests in Eurasia, Beijing Forestry University - French National Research Institute for Agriculture, Food and Environment (INRAE) for their supporting our work. We thank two anonymous peer reviewers and the handling editor for comments that improved the manuscript.

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Supplementary materials

Supplementary material 1

Tables S1, S2

Ge S, Gao T, Liu Y, Li J, Shi J, Ren L, Shi H (2025)

Data type: .zip

Explanation notes: Table S1. Metadata of sequences from literature used in this study. — Table S2. Metadata of sequences generated in this study.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.

Download file (19.98 kb)

Supplementary material 2

Figure S1

Ge S, Gao T, Liu Y, Li J, Shi J, Ren L, Shi H (2025)

Data type: .pdf

Explanation notes: A ladderized version of phylogenetic tree.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.

Download file (35.88 kb)