Contribution to the knowledge of Palaearctic species of Mesochorus GRAVENHORST: Subgenus Stictopisthus THOMSON (Hymenoptera, Ichneumonidae, Mesochorinae)

In this taxonomical survey, species of Mesochorus G RAVENHORST (subgenus Stictopisthus THOMSON) from the Palaearctic region are studied. New species are: Mesochorus (Stictopisthus) longistylus nov.sp. from Italy, Mesochorus (Stictopisthus) mandibulator nov.sp. from Mongolia, Mesochorus (Stictopisthus) nigrifrons nov.sp. from Europe and Russia, and Mesochorus (Stictopisthus) punjabi nov.sp. from Pakistan. Stictopisthus sacromontis SCHWENKE, 1999 is a new synonym of Mesochorus (Stictopisthus) bilineatus THOMSON, 1886. Stictopisthus madeirensis SCHWENKE, 1999 is a new synonym of Mesochorus (Stictopisthus) nemoralis (SCHWENKE, 1999). Stictopisthus hispanicus SCHWENKE, 1999 is a new synonym of Mesochorus (Stictopisthus) flavescens FONSCOLOMBE, 1852, and Stictopisthus polonius SCHWENKE, 1999 is a new synonym of Mesochorus (Stictopisthus) formosus BRIDGMAN, 1882. Mesochorus (Stictopisthus) dilutoides is a new name for Stictopisthus dilutus SCHWENKE, 1999 preoccupied in Mesochorus by RATZEBURG, 1844. The unknown ♂♂ of Mesochorus (Stictopisthus) maroccanus (SCHWENKE, 1999) and Mesochorus (Stictopisthus) ranini VIKBERG, 2017 and the unknown ♀ of Mesochorus (Stictopisthus) persicus RIEDEL et al., 2019 are described. All species are described and illustrated, and keys for the Palaearctic subgenera of Mesochorus and species of the subgenus Stictopisthus are provided.