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A cretaceous fly trap? Remarkable abdominal modification in a fossil wasp
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.
Given this diversity and the lack of information from a number of chrysidoid families, including the extant Plumariidae, it is not possible to infer potential hosts for † Sirenobethylus by mapping lifestyles on the phylogeny, although most of the aforementioned groups have also been reported from Kachin amber [ 39]. 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) The sixteen Kachin amber specimens (CNU-HYM-MA2015118 – CNU-HYM-MA2015133) reported in this study were purchased by Mr. Fangyuan Xia in April, 2015 and donated to the Key Laboratory of Insect Evolution and Environmental Changes, College of Life Sciences, Capital Normal University in May, 2016.
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