Vicilin (7S globulins) storage proteins from legume seeds were found to associate with chitin and chitin-containing structures. Several experiments have shown that they interfere with spore germination of filamentous fungi and with the sporulation of yeasts. The association of vicilins from non-host seeds with the chitin component of the mid gut of bruchids strongly deter development of these insects. The significance of this finding for the evolutionary discrimination of legume seeds by bruchids is discussed.