Halictoxenos xenomorphae, Zheng & Gong & Li & Zhou, 2025

Halictoxenos xenomorphae sp. nov.

http://zoobank.org/ urn:lsid:zoobank.org:act:

( Figs 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Description of female adults. Head, thorax and first abdominal segment fused into cephalothorax, without distinct suture ( Figs 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 ). Cephalothorax dark orange, flattened and pentagonal, total length ca. 0.70 mm, width ca. 0.62 mm, lateral margins straight, included angle ca. 60°; ventral side face up, ventral surface slightly convex and covered by alveolate sculpture, dorsal surface glabrous, attached to host’s abdomen, light colored and slightly concave ( Fig. 1A–D View FIGURE 1 ). Head located in front, front margin arced, almost glabrous ventrally ( Figs 2A–B View FIGURE 2 , 3A–B View FIGURE 3 , 4A–B View FIGURE 4 ). Clypeus and labrum delimited by indistinct suture, antenna invisible ( Fig. 2A–B View FIGURE 2 ). Mandible length ca. 0.03 mm, enclosed into mandibular capsule, pointing forward, flattened, rounded apically with a triangular sharp mandibular tooth, almost glabrous but with several micro tubercles on mandibular bulge; mandibular tooth present behind the mandible, angulation variable ( Figs 2B View FIGURE 2 , 3B View FIGURE 3 , 4C View FIGURE 4 ). Base of mandible almost reach lateral margin, distance between mandible base and mouth opening subequal to mandibular width ( Figs 2B View FIGURE 2 , 3B View FIGURE 3 , 4B View FIGURE 4 ). Maxilla and maxillary palp invisible ( Figs 2B View FIGURE 2 , 3B View FIGURE 3 , 4B View FIGURE 4 ). Mouth opening width ca. 0.24–0.25 mm, nearly U-shaped with sclerotized margin ( Figs 2B View FIGURE 2 , 3B View FIGURE 3 , 4B View FIGURE 4 ). Birth opening smoothly curved, forming a circular arc of approximately 90°, width ca. 0.07 mm ( Figs 2A View FIGURE 2 , 3A View FIGURE 3 , 4B View FIGURE 4 ). Thoracic segments fused with each other, covered by alveolate-aciculate sculpture ( Figs 2A View FIGURE 2 , 3A View FIGURE 3 , 4A View FIGURE 4 ). Mesosternum with 6–10 asymmetrical tiny papillae with C-shaped orifices which surrounded by light-colored spots ( Figs 2A View FIGURE 2 , 3A View FIGURE 3 , 4A View FIGURE 4 ). Central part of the metasternum and abdominal segment I dark brownish, spiracles located on lateral corners of cephalothorax, first sternite fused with metasternum and with depressed lateral margins ( Figs 2A View FIGURE 2 , 3A View FIGURE 3 , 4A View FIGURE 4 ). Abdomen without sclerotization, hide and occupy most space in host's abdominal cavity, ca. 2/3 length of host’s abdomen, filled by germ cells and first instar larvae ( Fig. 1C–D View FIGURE 1 ).

Description of first instar larva. Light to dark grey, body length ca. 120–160 µm ( Figs 3C View FIGURE 3 , 5A–C View FIGURE 5 ). Head broad and glabrous, front margin truncate, conical in lateral view. Eyes located on lateral margin of head with a large papillae under each eye, a sharp stout conical setae situate in front of eye near front margin with several micro papillae under its base ( Fig. 5A–D View FIGURE 5 ). Latero-ventral area of mouth opening with three tubercles and a short conical setae which similar to dorsal one ( Fig. 5A–D View FIGURE 5 ). Thorax glabrous but with spinules on posterior margin of each tergite, which arranged in a pattern of 1–2 short spinules between 2 long spinules, spinules on first thoracic segment much shorter; first thoracic tergite with a pair of dorsal papillae in central area and a pair of lateral papillae, both second and third thoracic segment with only a pair of lateral papillae; each thoracic sternite with several posterior spinules ( Fig. 5A–C View FIGURE 5 ). Coxae wide and slightly fused with thorax and with 1 slender and numerous short sharp spines, spines much shorter on fore-coxa; femora stout with several apical spines; tibiae slender and glabrous with short apical spine, tarsus of foreleg and midleg flattened, ca. 1/3 length of tibia, while hindleg tarsus similar to hind tibia; claws flattened and expanded, paddle-shaped ( Fig. 5C, E View FIGURE 5 ). Abdominal tergites similar to metathoracic tergite but without papilla, sternites with posterior spinules similar to tergites, segment X small and fused with segment IX, segment XI with two slender and glabrous caudal setae, length ca. 80–120 µm ( Fig. 5A–C View FIGURE 5 ).

Material examined. Holotype: female, China: Zhejiang Province, Nanjing City, Lin’an District, Tianmu Mountain , 30°24'33.14'' N, 119°29'12.19" E, 1025 m a.s.l., 26–29.V.2025, Xuhongyi Zheng, Dewen Gong leg. GoogleMaps Paratypes: 13 females, same data as the holotype GoogleMaps .

Diagnosis. The new species is characterized by (1) female cephalothorax mandible with sharp tooth on inner apical angle, (2) distance between mandible base and mouth opening subequal to mandibular width, (3) birth opening slightly and smoothly curved, and (4) spiracles located on lateral corners of the cephalothorax.

The new species can be attribute to Halictoxenos by parasitic in Lasioglossum sp. of Halictidae , relatively sharply pointed and light-colored cephalothorax with dark metasternal area and abdominal segment I, mandibles with sharp mandibular tooth, maxillae and maxillary palp almost invisible, and mesosternum with conspicuous papillae in the central area. Compared with the 9 Asian Halictoxenos species, female cephalothorax of the new species can be separated from H. hondonis , H. latifemoralis , H. nambui by having distinct sharp mandibular tooth, from H. duplicis by intermandibular distance wider than the breadth of mouth opening, from H. evylaei by curved birth opening margin, from H. japonicus by less curved birth opening margin, from H. borealis by much wider distance between mandible and mouth opening, from H. robbii by lacking median darkish pattern, and from H. manilae by the location of mandibular tooth. It can be distinguished from the three European species by a slightly angular birth opening, distinct medial spots and sharp mandibular tooth.

Compared with other species with well-described planidia, planidia of H. xenomorphae sp. nov. can be distinguished from H. knereri by much longer caudal setae and shorter spinules on thoracic sternites, from H. fortunatus by bearing spinules on the third thoracic sternite.

Etymology. The species is named after xenomorph from the Alien series of movies, in reference to their similar parasitic and mysterious life history.

Distribution. China ( Zhejiang).

Biological notes. Field observations were conducted in Tianmu Mountain in 2023–2025. A single female H. xenomorphae sp. nov. was found protruding from a male Lasioglossum sp. resting on shrub leaves in 16 June 2023 and 30 May 2024, respectively ( Fig. 6 View FIGURE 6 ). Although dozens of bees were photographed and examined in 2023 and 2024, their exact numbers and detailed behaviors were not systematically recorded.

From 26 to 29 May 2025, we performed targeted observations to study the biology of this undescribed parasitic species. A comprehensive survey covering approximately 400 m ² was conducted at the mountain summit using visual surveys and sweep netting, with particular attention given to flowering plants frequently documented in studies of Stylopidae and Xenidae . All collected bees were kept alive and examined under a stereomicroscope after brief, non-lethal refrigeration. Most non-stylopized bees were released on the final day, except for 100 males and all females retained for further analysis.

During the May 2025 survey, more than 500 bees were collected, including 528 individuals of the host Lasioglossum species ( 496 males and 32 females). 14 neotenic females of the strepsipteran H. xenomorphae sp. nov. were collected—each infecting a single host—while no males were detected. Despite the scarcity of female hosts, their parasitism rate (25%, 8/32) far exceeded that of males that were parasitized (ca. 1.21%, 6/496). Additionally, dissections of 30 non-parasitized males and all non-parasitized females revealed no developing parasite larvae in their abdomens.

Lasioglossum sp. were active from 9:00 to 17:00 daily, after the sunrise. The bees preferred open areas near mountain trails. Despite the presence of ≥10 flowering plant species in the sampling area, Lasioglossum sp. exhibited relatively low floral visitation rates; though we paid special attention to flowers, only 20 individuals (both sexes) were captured on Quercus sp. inflorescences, all of which were non-stylopized. Males predominantly aggregated on shrub tops ( 20 cm – 4 m height), either resting or engaging in chase behaviors, whereas females were sporadically observed on shrubs or grasses.

All the female H. xenomorphae sp. nov. were found with the cephalothorax protruding from the tergite 4 of the host, either on the left or the right side, with no lateral preference. No obvious morphological differences distinguished stylopized from non-stylopized bees ( Fig. 7A–H View FIGURE 7 ). Female hosts possessed larger abdomens than males, and their H. xenomorphae sp. nov. parasites were significantly larger, consistently containing mature planidia. In contrast, when male hosts were parasitised they were smaller, and the female H. xenomerphae sp. nov. had only developing eggs. Planidial development varied: some females' abdomens were entirely packed with mature planidia, while others had few or none. Mature planidia were encased in the brood canal at the anterior body region, and was connected to the cephalothorax.

Molecular study. Sequences of 6 Halictoxenos species are available from GenBank. We sequenced the COI gene of our H. xenomorphae sp. nov. specimens and compared them to those sequences. Sequences of the two Japanese species, H. japonicus and H. hondonis , cannot be aligned with other sequences, thus excluded in this study. The genetic distances between the five species ranging from 0.150 to 0.340, 0.254 in average. The 0.185 distance between H. xenomorphae sp. nov. and H. spencei is the second lowest data in the Table 1.