Abstract The semiaquatic grasshopper Cornops aquaticum Bruner, which is highly specific of Eichhornia crassipes (Pontederiaceae), constitutes one of the most abundant herbivores in the Neotropical wetlands and a possible biological control agent of this weed in South Africa. The aims of this study were 1) to assess the performance of each age category of C. aquaticum on crop plants and the host plant E. crassipes; 2) to assess the feeding preference of this grasshopper on crop plants in the presence and absence of E. crassipes; and 3) to determine the presence of nymphs and adults of this grasshopper on crops and in the adjacent wetlands where Eichhornia plants are present. Crop plants included in this study were Zea mays, Oryza sativa, Saccharum officinarum and Ilex paraguariensis. The age categories of C. aquaticum population were nymphs A (instar I and II), nymphs B (instar III to VI) and adults (females and males). To assess grasshopper performance on E. crassipes and crop plants, survival and oviposi...