Chitin-binding vicilin from Erythrina velutina seeds was purified by ammonium sulfate followed by affinity chromatography on a chitin column and gel filtration on Superose-6-10-300-GL. The Erythrina velutina vicilin, called EvV, is a tetrameric glycoprotein composed of 1.85% carbohydrates and M r of 216.6 kDa, consisting of two subunits of M r of 54.8 and two subunits of M r of 50.8 kDa. The EvV homogeneity was confirmed in native PAGE where it was observed to be a unique acid-protein band with slow mobility in this gel. Effect of EvV on C. capitata larvae was examined by bioassay and its mechanism of action was determined by immunodetection techniques and fluorescence localization in chitin structures that are present in C. capitata digestory system. EvV when added to diet caused strong effect on mortality (ED50 of 0.14%) and larval mass (WD50 of 0.12%). These deleterious effects were associated to the binding to chitin structures present in peritrophic membrane and to gut epithelial cells, and its low digestibility in C. capitata digestive tract. These results are the first demonstration of a proteinaceous bioinsecticide from plant origin effective against C. capitata larvae. EvV may be part of the pest management programs or an alternative in plant improvement program.