Genes of three naturally occurring monocot mannose-binding lec- tins from snowdrop (Galanthus nivalis L. agglutinin, GNA), garlic (Allium sativum L. leaf agglutinin, ASAL), and onion (Allium cepaL. agglutinin, ACA) and a recombinant fusion lectin between ASAL and ACA genes were expressed in a bacterial system. The pure and active form of the recombinant lectin peptides were utilized for estimation of their sensitivity potential against feeding nymphs of mustard aphid (Lipaphis erysimi (Kaltenbach)), a major sap-sucking insect pest of Indian mustard (Brassica juncea (L.) Czern.), an oilseed crop. The artificial diet bioassay revealed that ACA and the fusion lectin con- tained higher toxicity potential than GNA and ASAL. Ectopic ex- pression of these lectins in mustard plants confirmed their protective capacity on the development of the population of aphids on transgenic plants. Based on the strong possibilities that lectins originating from diverse sources would have differential insecticidal potential against different insects, deployment of the appropriate lectin gene figures as crucial in the transgenic approach to protect crop plants against sap- sucking insect pests.