Ureases are nickel dependent metalloenzymes, that hydrolyze urea to ammonia and carbon dioxide, widespread among plants, fungi and bacteria. Urease (EC 3.5.1.5) of jackbean (Canavalia ensiformis) seeds was the first protein ever to be crystallized. Canatoxin, an urease isoform in these seeds is toxic to insects and fungi, suggesting that it may have an important role in plant defense. The entomotoxic effect is due to the release of a 10kDa peptide by cathepsins-like enzymes in the insect's midgut, being this unrelated to its ureolytic activity. Jackbean urease and soybean ureases are also insecticidal. A pest of cotton culture, the hemipteran Dysdercus peruvianus is used as one of experimental models in these studies. Nymphs of D. peruvianus are affected by jackbean ureases while adults insects are not. We are now studying the proteolytic processing of ureases by the insects seeking an explanation for this difference.  Midgut homogenates of 4th instars or adults were prepared and their proteolytic activity upon azocasein was determined (One unit of azocaseinolytic activity defined as the amount of enzyme(s) able to produce increments of 0.001 A420/h at 37º at pH 5.6). The in vitro hydrolysis of jackbean urease was performed by incubating urease with midgut homogenates during 24 hours, followed by SDS-PAGE and Western blot with anti-urease antibodies to determine the fragmentation pattern. Under the above conditions, we observed hydrolysis of urease with both adult’s and 4th instar’s enzymes, but only nymphs midguts homogenate hydrolyzed urease into fragments of about 10kDa. Bioassays to determine the toxicity of these fragments are under way. Our data suggest that differences in fragmentation pattern of urease with proteolytic enzymes of nymphs and adults of D. peruvianus may explain their susceptibility to the insecticidal effect of jackbean ureases.