To detect biocontrol agents of the invasive aquatic weed Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae), surveys were conducted in the basins of the Paraná and Uruguay rivers in Argentina and the basin of the Amazon river in Peru and Brazil. Among the captured delphacids, Megamelus scutellaris Berg was the most abundant. Berg originally described this species on the basis of a macropterous female. In this contribution, the macropterous and brachypterous male and the brachypterous female are described, and the holotype female is redescribed. Some biological aspects are recorded.