A case of frozen behaviour: A flat wasp female with a beetle larva in its grasp in 100-million-year-old amber

Parasitism, a malignant form of symbiosis, wherein one partner, the parasite, derives benefits to the detriment of another, the host, is a widespread phenomenon. Parasitism sensu lato is understood here to include many phenomena, like parasitoidism, kleptoparasitism, phoresy and obligate parasitism. Insecta has many in-groups that have evolved a parasitic life-style; one of the largest in-groups of these is probably the group of Hymenoptera. Bethylidae, the group of flat wasps, is a smaller in-group of Aculeata, the group of hymenopterans with venom stings; representatives of Bethylidae are parasitic. They are more specifically larval ectoparasitoids, meaning that their immature stages are externally developing parasites that kill their host organism at pupation (end of interaction). They mostly parasitise immature representatives of Coleoptera and Lepidoptera. Female flat wasps search for a host for their progeny, paralyse it with their venom sting and then oviposit onto it. Herein we describe one of the oldest findings of parasitic interactions of parasitoid wasps with their progenies’ hosts, specifically a flat wasp female grasping and (potentially) stinging a beetle immature in Cretaceous Kachin (Myanmar) amber (ca. 100 million years old). This finding indicates that this type of parasitic interaction existed since the Cretaceous, temporally close to the earliest findings of representatives of Bethylidae.