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| Sirenobethylus charybdis Wu, Vilhelmsen & Gao, in Wu, Vilhelmsen, Li, Zhuo, Ren et Gao, 2025. |
Abstract
Background: Carnivorous insects have evolved a range of prey and host capture mechanisms. However, insect predation strategies in the fossil record remain poorly understood.
Results: Here, we describe †Sirenobethylus charybdis n. gen. & sp., based on sixteen adult female wasps in Kachin amber from the mid-Cretaceous, 99 Mya (million years ago), and place it in Chrysidoidea: †Sirenobethylidae n. fam. The fossils display unique morphological modifications on the tip of the abdomen consisting of three flaps from the modified abdominal sternum 6 and tergum and sternum 7; the lower flap formed from sternum 6 is preserved in different positions relative to the other flaps in different specimens, indicating that they form some sort of grasping apparatus. Nothing similar is known from any other insect; the rounded abdominal apparatus, combined with the setae along the edges, is reminiscent of a Venus flytrap. Phylogenetic analysis suggests that the new family is a separate lineage close to the base of Chrysidoidea.
Conclusions: †Sirenobethylus probably was a koinobiont parasitoid wasp; the abdominal grasping apparatus may have been used to temporarily immobilize the host during oviposition. The new fossils suggest that Chrysidoidea displayed a wider range of parasitoid strategies in the mid-Cretaceous than they do today.
Keywords: Sirenobethylidae, Chrysidoidea, Morphology, Grasping apparatus, Phylogeny
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| †Sirenobethylus charybdis sp. nov., holotype (specimen CNU-HYM-MA2015124) female. A Dorsal view as preserved. B The tip of abdomen and ovipositor in ventral view, showing trigger hairs (black arrows). C The tip of abdomen and ovipositor in lateral view, showing trigger hairs (black arrows), ovipositor (orange arrow) and groove on the sternum 7 (blue arrow). D Habitus reconstruction. Scale bars: A 0.5 mm; B 0.3 mm; C 0.2 mm. Abbreviations: S6 sternum 6; T7 tergum 7; S7 sternum 7 |
Systematic paleontology
Order Hymenoptera Linnaeus, 1758.
Infraorder Aculeata Latreille, 1802.
Superfamily Chrysidoidea Latreille, 1802.
Family †Sirenobethylidae Wu, Vilhelmsen & Gao fam. nov.
Type genus. †Sirenobethylus Wu, Vilhelmsen & Gao gen. nov.
Diagnosis. Head hypognathous, with medial line on vertex. Antenna with nine flagellomeres, antennal sockets simple, close to posterior margin of clypeus; clypeus projecting and acute in lateral view, slightly convex; mandibles with four apical teeth along truncate apical margin; occipital carina distinct, complete. Propleuron not exposed in dorsal view; prosternum small, diamond-shaped, exposed; notauli present. Female macropterous. Second abdominal (first metasomal) segment in dorsal view with angular anterolateral corners; tergum 7 longer than wide, distinctly narrower than other terga; sternum 6 wider than other sterna, laterally expanded distally, paddle-shaped, projecting posteriorly, posterior margin concave, with a dozen very long, slender setae; many thick spines on dorsal surface of sternum 6. Sternum 7 with median part accommodating ovipositor shaft dorsally and two lateral parts curving outwards before approaching median part distally; median and lateral parts of sternum 7 separated by weakly sclerotized areas. Sting sheaths on either side of the sting, apparently shorter than sting.
Genus †Sirenobethylus Wu, Vilhelmsen & Gao gen. nov.
Type species. †Sirenobethylus charybdis Wu, Vilhelmsen & Gao sp. nov.
Etymology. The new generic name is a combination of the Greek ‘sireno-’ meaning ‘female humanlike beings with alluring voices in Greek mythology’, and ‘bethylus’, from the nominal genus of Bethylidae. ‘Sireno-’ is also a reference to Mammalia: Sirenia, as the ‘tail’ of the wasp in ventral view resembles that of a manatee. The gender is masculine.
†Sirenobethylus charybdis Wu, Vilhelmsen & Gao sp. nov.
Etymology. The epithet refers to Charybdis, the sea monster in Greek mythology who alternately swallowed and disgorged copious amounts seawater three times a day.
Materials. Holotype. Female, CNU-HYM-MA-2015124.
Locality and horizon. The amber specimen was collected from Kachin (Hukawng Valley) of northern Myanmar, which is dated at 98.79 ± 0.62 Mya [17, 18].
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| Bayesian phylogenetic tree based on morphological characters. The large black dots show the age of the Kachin amber species; the branch nodes of this phylogenetic tree are not time-calibrated, the geological time scale refers only to the fossil taxa. The numbers on the branch nodes are posterior probabilities. Green branches: Chrysidoidea; blue branches: Vespoidea; orange branches: Apoidea. Families with habitus images associated indicated in purple: †Sirenobethylus charybdis (Sirenobethylidae), Chrysis ignita (Chrysididae), Pristocera depressa (Bethylidae), Embolemus ruddii (Embolemidae), Rhopalomutilla carinaticeps (Mutillidae), Polistes nimpha (Vespidae), Scolia quadripunctata (Scoliidae), Formica rufa (Formicidae) |
Qiong Wu, Lars Vilhelmsen, Xiaoqin Li, De Zhuo, Dong Ren and Taiping Gao. 2025. A Cretaceous Fly Trap? Remarkable Abdominal Modification in A Fossil Wasp. BMC Biology. 23, 81. DOI: doi.org/10.1186/s12915-025-02190-2 [27 March 2025]
