The estimation of biomass in insect populations is a key factor to quantify the available resources and energy fluxes in ecosystems food webs. <span name="style_italic">Cornops aquaticum</span> is a common herbivore in <span name="style_italic">Eichhornia</span> plants in wetlands of Northeast Argentina. We aimed to analyse its biomass variation, related to the different grasshopper age categories populations in two host-plants: <span name="style_italic">Eichhornia azurea </span>and<span name="style_italic"> Eichhornia crassipes</span>. For this, standard samplings of <span name="style_italic">C. aquaticum</span> populations were carried out with an entomological net of 70cm diameter in two wetlands with <span name="style_italic">E. azurea </span>and<span name="style_italic"> E. crassipes</span>, in Corrientes and Chaco Provinces; besides, dry weight was also obtained (directly and indirectly), and a regression model to indirectly estimate the biomass from a linear dimension measure (hind femur length) is proposed. A total of 2 307 individuals were collected and separated in different age categories; their abundance and linear dimension data were obtained. The model proposed was lnDM=lna+b*lnH (where DM=dry mass, <span name="style_italic">a</span> and <span name="style_italic">b</span> are constants and H=hind femur length) (R<span name="style_sup">2</span>=0.97). The population biomass variations of C. aquaticum were due to the relative abundance of each age category and the grasshopper individual dry weight. No significant differences were found between populations biomasses obtained by direct and indirect methods in <span name="style_italic">E. azurea </span>and<span name="style_italic"> E. crassipes</span> floating meadows. This model made easier the <span name="style_italic">C. aquaticum</span> biomass calculation for both individuals and the population, and accelerated the processing of high number of samples. Finally, high biomass values of populations and individual age category (especially in adults) emphasize the importance of <span name="style_italic">C. aquaticum</span> as a consumer and a resource for predators on <span name="style_italic">Eichhornia</span> floating meadows food webs. Rev. Biol. Trop. 63 (1): 127-138. Epub 2015 March 01. floating meadows food webs. Rev. Biol. Trop. 63 (1): 127-138. Epub 2015 March 01.

peso seco; Eichhornia; fémur; acridio semiacuático; modelo de regresión; abundancia poblacional; lirio de agua