The aim of this paper is to shed light on the boundaries of two sympatric species of Cuernavaca, C. inexacta and C. longula, to enable further ecological studies. Species in this genus are associated with water hyacinths in wetlands of Northeastern Argentina (Paraná-Paraguay waterway system) and the Peruvian Amazon. This work lists new host records for Cuernavaca, which include Pontederia crassipes, P. cordata, P. subovata and P. rotundifolia (Pontederiaceae). A redescription for C. inexacta with new diagnostic genitalic features is also provided, as well as an updated identification key and a distribution map. The genus is distributed throughout Central and South America, reaching north and central Argentina in its southernmost distribution.