Cornops aquaticum (Bruner, 1906) is a semi-aquatic acridid (Orthoptera, Tetraeniini) with a wide geographical distribuition, ranging from the South of Mexico (23°N) to Uruguay and the Northeast of Argentine (35°S). These grasshoppers can be found on leaves of the aquatic macrophyte Eichhornia spp. where they pass their life cycle. The study site “Sítio das Acácias” was located between the subdistricts of Ferraz and Ajapi (22°16’S, 47°34’W) near Rio Claro-SP, Brazil. Adult specimens were collected during daylight with the help of an entomological net in a flooded area affected by cattle, about 20m from the Corumbataí River. The body mass (g) and volume (ml) were measured in 3 males and 15 females. Relations between body mass (M) and volume (V) were obtained and are expressed by the equations V(male) = 0,1132 + 0,5543 . M; V(female) = 0,0893 + 1,0667 . M and V(male and female) = -0,0355 + 1,4860 . M. The correlation coefficients (r) (males = 0,41; females = 0,68; both sexes = 0,89) were significant (P<0,05 for males and females, P<0,01 for both sexes). The positive relation “body mass versus volume” in C. aquaticum also showed that the proportion of volume in relation to size does not depend on sex. Data are statistically reliable and calculations allow that body volumes are mathematically inferred from weight data in studies that need these parameters for routine calculations, such as respirometric constants of the Warburg respirometer.

Index terms: grasshopper, size, sex