Perithous

Distinguished from similar pimpline genera by larval characters: mature larvae have maxillary and labial palpi with more than two sensilla. Final instar larvae can be differentiated from other Perithous species by presence/absence of spinules on tegument, number and arrangement of setae on cranial sclerites and mouthparts, and degree of epistoma development. Adults recognized by combination of large size, long ovipositor, and black coloration with yellow facial markings.

Associated with woodland habitats where solitary stem-nesting apoid wasps occur. Nests within pre-existing cavities in wood, hollow stems, or tunnels through pith of broken twigs or berry canes created by host wasps.

Palaearctic region, extending as far east as Japan. In Britain, first recorded from England in 1997 as a recent colonist, subsequently spreading across much of southern England and reaching Yorkshire by 2004. GBIF records from Denmark, Norway, and Sweden.

Idiobiont ectoparasitoid feeding externally on larvae of solitary stem-nesting apoid wasps. Perithous larvae have been observed to consume other parasitoid larvae that previously attacked the same host.

• Ectemnius - hostrelatively large Crabronidae of this genus are known hosts
• solitary stem-nesting apoid wasps - hostgeneral host group; larvae attacked in their nests
• other parasitoid larvae - prey/predatorconsumed by Perithous larvae when co-occurring on same host

Complete metamorphosis. Final instar larvae described; species pupates after larval development. Female attacks host larvae in their nests, permanently paralyzes host, and lays egg for external feeding. Multiple cells may be created in linear or branching tunnels.

Females hunt host larvae in their colonies, plucking them from stems and leaves, stinging them into permanent paralysis, and transporting them back to nest. Females create partitions of chewed plant pith or sawdust to close completed cells and form base of next cell; partitions can exceed 25 mm in thickness, possibly to deter parasites. Females have been observed guarding nest entrances to chase off potential parasites or competitors. Males wait outside nest tunnels to mate with emerging females.

Parasitoid controlling populations of solitary stem-nesting apoid wasps. Member of Pimplinae tribe Perithoini, which are almost exclusively parasitoids of other Hymenoptera. Competes with small carpenter bees (Ceratina spp.) for nesting sites.

Subject of genome sequencing as part of Darwin Tree of Life project. Artificial nesting blocks with small-diameter holes can attract related wasps, though Perithous itself is not commercially reared. Occasionally mistaken for pest species indoors, though these wasps are solitary and do not nest in buildings.

• ZatypotaBoth pimpline ichneumonids with similar larval morphology; distinguished by stipital sclerite expansion at lateral end and differences in setae arrangement on cranial sclerites and mouthparts in final instar larvae
• PemphredonBoth associated with stem-nesting wasp habitats and aphid predation/parasitism; Pemphredon are small Crabronidae that prey on aphids and are hosts for Perithous, which are larger ichneumonid parasitoids with different biology
• OmalusTiny cuckoo wasps that parasitize nests of aphid wasps including Pemphredon; much smaller and different family (Chrysididae) than Perithous

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Bug Eric: Aphid Killers: Pemphredon Wasps
• Descriptions of the Final Instar Larvae of Perithous septemcinctorius, Zatypota bohemani and Z. gracilis (Hymenoptera: Ichneumonidae: Pimplinae)
• The genome sequence of an ichneumonid wasp, Perithous albicinctus (Gravenhorst, 1829) (Hymenoptera: Ichneumonidae).