A new species of Leptoconops Skuse from Argentina, description of the male of L. casali Cavalieri amp; Chiossone and a key to the Neotropical species (Diptera: Ceratopogonidae).

A new species, Leptoconops (Proleptoconops) chacoensis, is described and photographed from a female collected in a forest area of the Chaco province, Argentina. This is the first record of the subgenus L. (Proleptoconops) Clastrier from the Neotropical region south of Mexico, and the new species is compared with L. (P.) werneri Wirth Atchley from southern USA and Mexico and L. (P.) aviarum from Tajikistan. Besides, the first description of the male of L. (Leptoconops) casali Cavalieri Chiossone is provided, from males collected associated with females in La Rioja and La Pampa provinces, Argentina, and this species is newly recorded from several areas of the country, significantly enlarging its geographical distribution. In addition, a key to Neotropical species of the genus is provided.