© 2020, Sociedade Entomológica do Brasil. Nesomesochorinae is a rather small subfamily of Darwin wasps (Insecta: Hymenoptera: Ichneumonidae), only with three described genera. We recognize a fourth nesomesochorine genus from Perú and describe it as a new genus, Bina Shimizu & Alvarado gen. nov. The new genus is distinguished from previously described genera of Nesomesochorinae by the following combination of character states: mandible parallel-sided proximally and abruptly strongly narrowed ventroapically so that its lower apical tooth is much smaller and sharper than upper tooth; propodeum with lateromedian longitudinal carinae between anterior and posterior transverse carinae developed on more than posterior 0.9 so that the area superomedia is more or less enclosed; thyridium of 2nd metasomal tergite sometimes very large; 1st metasomal tergite stout and arched; body highly shiny. Binagen. nov. comprises two species also described as new to science: B. huayrurae Shimizu & Alvarado sp. nov. (type species of Binagen. nov.) and B. nigra Shimizu & Alvarado sp. nov. Identification keys to genera of Nesomesochorinae and to species of Binagen. nov. are provided.