Introduction
The genus Aximopsis sensu lato Ashmead, 1904 (Eurytomidae) was re-defined by Lotfalizadeh et al. (2007) to include Conoaxima Brues, 1922, Eurytomaria Masi, 1943, Mesoeurytoma Cameron, 1911, Aximogastroma Narendran, 1994 and the Eurytoma nodularis Boheman, 1836 species group. This genus is currently recognised, based on a suite of homoplastic morphological characters: postgenal laminae raised, prepectus with a strong medioventral tooth, subventral carinae of prepectus delimiting a raised surface, subventral prepectus with a deep pit, mesopleuron with a horizontal ventral shelf and a completely delimited epicnemium (Lotfalizadeh et al. 2007, Gates et al. 2025). The 43 described species of Aximopsis s.l.. are found worldwide, except in Australia and Antarctica (UCD Community 2023) and the genus includes many undescribed species in tropical regions. Aximopsis are parasitoids of endophytic insects living in branches, stems or leaf mines; most known species are parasitoids of Coleoptera, Lepidoptera and Hymenoptera (Zerova and Seryogina 2006, Lotfalizadeh et al. 2006, Lotfalizadeh et al. 2007, Gates and Delvare 2008, Gates 2009, Lotfalizadeh and Hosseini 2014, Delvare et al. 2019, Naghizadeh et al. 2019, Lotfalizadeh et al. 2020, UCD Community 2023).
About half of the known Aximopsis s. l. species belongs to the nodularis group, which can be recognised by the presence of: 1) a conspicuous mesopleuron ventral shelf; 2) carinate fore coxae; 3) distinctly petiolate female metasoma; and 4) male funicular segments with two convex apices and covered with long pubescence (Lotfalizadeh et al. 2007, Lotfalizadeh and Hosseini 2014). The nominal species Aximopsis nodularis is a European species with a wide host range that includes Apidae (including Ceratina Latreille, 1802), Curculionidae, Cynipidae, Ichneumonidae, Sphecidae and Vespidae (UCD Community 2023). Other members of the nodularis group have been recorded as parasitoids of Coleoptera (Anthribidae, Buprestidae, Chrysomelidae (Bruchinae)), Diptera (Tephritidae), Hymenoptera (Apidae, Cynipidae) and Lepidoptera (Coleophoridae, Noctuidae, Pyralidae) in the Afrotropical, Neotropical and Palearctic Regions (UCD Community 2023). The placement of this group is unstable: as most were originally described within Eurytoma Illiger, 1807 and subsequently moved to Aximopsis (Lotfalizadeh et al. 2006, Zerova and Seryogina 2006, Lotfalizadeh et al. 2007, Gates and Delvare 2008, Gates 2009, Lotfalizadeh and Hosseini 2014, Delvare et al. 2019, Naghizadeh et al. 2019, Lotfalizadeh et al. 2020, UCD Community 2023). Recent phylogenomic analyses have recovered a paraphyletic relationship between Aximopsis s.l.. and genera, such as Chryseida Spinola, 1840 and Axima Walker, 1862 (Zhang et al. 2025, Park et al. 2026); thus, the placement of the species group will likely change in light of revision (G. Delvare, pers. comm.).
Species from multiple genera of eurytomines have been recorded in association with Ceratina, including Axima zabriskiei Howard, 1890 on C. dupla Say, 1837 and C. calcarata Robertson, 1900 in North America (Vickruck et al. 2010); Aximopsis nodularis on C. callosa (Fabricius, 1794) in Europe (Zerova and Seryogina 2006); and Eurytoma apiculae Bugbee, 1966 on C. dallatorreana Friese, 1896, C. nanula Cockerell, 1897, C. punctigena Cockerell, 1916 and possibly C. calcarata in North America (Bugbee 1966, Vickruck et al. 2010). Additionally, records of undescribed Eurytoma species have been documented on C. australensis (Perkins, 1912) in Australia (Vickruck et al. 2010).
Here, we describe a new species of eurytomine reared from the larvae of Ceratina smaragdula (Fabricius, 1787) from Hainan Province of China that belong to the nodularis group and we tentatively place it within Aximopsis s.l..
Materials and methods
Insect collection
The host bee Ceratina smaragdula naturally utilises dead twigs of Scaevola taccada (Asterales, Goodeniaceae) for nesting. To obtain nests of this host and thereby rear its parasitoid, we collected nest‑bearing twigs from two sources: (1) naturally occurring dead twigs along roadsides with visible nesting signs (a circular entrance hole and accumulated wood dust) and (2) artificial trap nests made of sun‑dried twigs placed in PVC holders near S. taccada thickets. Nest collection was conducted in Wenchang Town (19°33'N, 110°46'E) of Wenchang City and Yongxing Island (16°50'N, 112°20'E) of Sansha City, Hainan Province from September 2023 to December 2025, covering the peak nesting season of the host bees. All occupied twigs were gathered at dusk and sealed with tape to prevent adult insect escape.
In the laboratory, each twig was dissected longitudinally under a Nikon SMZ25 stereomicroscope. Brood cells containing parasitoid larvae or pupae were kept individually in ventilated tubes at room temperature and checked daily for adult emergence. The last parasitoids emerged in June 2026 in the laboratory. Emerged adults of parasitoids were preserved in 100% ethanol for morphological and molecular studies. All nest tubes containing insect brood (including parasitoid larvae, pupae or host remains) were preserved in 100% ethanol for further examination.
Specimens of Aximopsis qiong sp. nov. are deposited in two institutions: South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China (SCBG); and Institute of Zoology, Chinese Academy of Sciences, Beijing, China (IZCAS).
Morphological terminology and abbreviations
Terminologies follows Burks et al. (2025) for general chalcidoid morphology and Lotfalizadeh et al. (2007) for eurytomid-specific terms. The following measurements and abbreviations were used: F1–Fn, the first and the following flagellomeres; POL (post-ocellar distance), the distance between the inner margins of the posterior ocelli; OOL (ocellar–ocular distance), the distance from the outer margin of lateral ocellus to the inner margin of compound eye; LOL (lateral–ocular distance), the distance between lateral and frontal ocelli; and Gt1–Gtn, the first and the following gastral tergites.
DNA sequencing and molecular analyses
Genomic DNA was extracted from the right fore-leg of four specimens using the TIANamp Micro DNA Kit (Tiangen Biotech, Beijing, China) following the protocol of Taekul et al. (2013). The mitochondrial cytochrome oxidase subunit 1 (COI) gene sequences were amplified as described in Chen et al. (2023).
For phylogenetic analysis, Phylloxeroxenus sp. Ashmead, 1888 (GenBank accession: PV031844) was selected as the outgroup. In addition, COI sequences of related taxa (Delvare et al. 2019, Zhang et al. 2025) were downloaded from GenBank, including Chryseida bennetti Burks, 1956 (PV031771), Chryseida burksi Zerova, 1980 (PV031772), Chryseida sp6 (PV031775), Aximopsis sp1 (PV031741), Aximopsis sp2 (PV031742), Aximopsis sp. (MH878925), Aximopsis gabrielae Zhang, Gates & Campos, 2022 (PV031740), Aximopsis balajasi Delvare, 2019 (MH878922, PV031738) and Aximopsis collina (Zerova, 1984) (MH878923, PV031739). In total, 16 COI sequences, including the four obtained from the Chinese specimens (GenBank Accessions PZ568852-PZ568855), were used for phylogenetic analysis. The phylogenetic tree was reconstructed using IQ-TREE v.3.1.2 (Wong et al. 2026) under a Maximum Likelihood framework, using ModelFinder (Kalyaanamoorthy et al. 2017) to find the best evolutionary model. To assess support, we performed 1000 Ultrafast Bootstrap (UFBoot, Hoang et al. (2017)), along with ‘-bnni’ to reduce the risk of overestimation. The resulting tree was visualised with iTOL v.7 (Letunic and Bork 2021) and further refined in Adobe Illustrator 2025.
Imaging
Multifocal images of voucher specimens deposited in SCBG were produced using a Nikon SMZ25 microscope, equipped with a Nikon DS-Ri 2 digital camera system (Melville, NY, USA). Photographs of live insects were taken with a Canon 5D Mark IV camera (Tokyo, Japan) fitted with a 100 mm macro lens. Image plates were subsequently assembled and post-processed using Adobe Photoshop CS6 Extended.
Discussion
This study reports Aximopsis qiong sp. nov., a new species of eurytomid parasitoid reared from larvae of the small carpenter bee C. smaragdula in Hainan, China. From a taxonomic perspective, A. qiong represents the first record of the genus Aximopsis from China and only the second species recorded in association with Ceratina nests, following A. nodularis (UCD Community 2023). The sister-group placement of A. qiong with other members of the Palaearctic nodularis group is only weakly supported by COI data, underscoring the need for a comprehensive taxonomic revision of Aximopsis sensu lato to clarify phylogenetic relationships amongst the cosmopolitan Aximopsis and the two New World genera Axima and Chryseida.
Beyond its taxonomic significance, the discovery of A. qiong carries important ecological and management implications, given the role of its host. Ceratina smaragdula is a widely distributed pollinator across southern Asia and plays a significant role in sustaining both natural plant communities and agricultural productivity through its pollination services (Ali et al. 2024). On Hainan Island and its associated archipelagos, this bee represents a particularly important wild pollinator in coastal ecosystems, where it extensively utilises dead twigs of the native littoral shrub S. taccada for nesting (unpublished data). Our field surveys reveal that this key pollinator is subject to significant parasitoid pressure from A. qiong. This gregarious ectoparasitoid exhibits a strongly female-biased sex ratio (3.6♀:1♂), a trait that would be expected to exacerbate its negative impact on the reproductive success of local C. smaragdula populations.
These findings raise a critical concern for pollinator management. Artificial trap nests constructed from native plant materials (like S. taccada twigs in this study) are increasingly recognised as an effective strategy for monitoring and augmenting solitary bee populations to enhance pollination services (Rahimi et al. 2021). Our results confirm that C. smaragdula readily accepts such nests, making it a promising candidate for managed population enhancement in island and coastal restoration projects (unpublished data). Nevertheless, without appropriate precautions, trap nests may inadvertently function as concentrated breeding resources for A. qiong, facilitating its local population increase and intensifying parasitism pressure on the targeted pollinator. Under such conditions, trap-nesting initiatives risk undermining or even reversing their intended conservation outcomes (MacIvor and Packer 2015). To prevent the inadvertent introduction and amplification of A. qiong in managed bee populations, we recommend that trap-nesting programmes implement routine inspections and, where feasible, remove or destroy parasitised brood cells prior to parasitoid emergence.
Notably, C. smaragdula has recently been documented as an invasive species in Hawai'i (Shell and Rehan 2017). While this invasive context might invite speculation about the potential use of of A. qiong for biological control, the lack of host specificity documented in congeners, such as A. nodularis, makes such application highly uncertain. More importantly, the primary value of documenting A. qiong in its native range lies in the warning it provides for local conservation: in Hainan, where C. smaragdula serves as a key pollinator, trap‑nesting programmes could inadvertently spread this parasitoid and undermine pollination services. Management efforts should, therefore, prioritise excluding A. qiong from augmented C. smaragdula populations, rather than promoting it as a biocontrol agent.