Different antimetabolic effects of related lectins towards nymphal stages of Nilaparvata lugens

Insect feeding trials were carried out to determine the effects of a range of mannose-specific lectins on third instar nymphs of the rice brown planthopper (BPH), Nilaparvata lugens. Sta˙l. Dose response curves show that Galanthus nivalis agglutinin (GNA) has the strongest toxic effect of the lectins tested, and is effective at concentrations considerably lower than those previously reported. Narcissus pseudonarcissus agglutinin (NPA) and Allium sativum agglutinin (ASA) exhibit a significant antimetabolic effect towards the insect but were less effective (on a molar basis) than GNA. LC 50 values for GNA, NPA and ASA are approximately 4 μM, 11 μM and > 40 μM respectively. These mannose-specific lectins are serologically identical, but differ in the number of subunits per protein molecule; ASA is a dimer, NPA is a trimer and GNA is a tetramer. The results obtained support the hypothesis, that the effectiveness of the mannose-binding lectins as antimetabolites is determined by the number of subunits per molecule. Two N-acetylglucosamine binding lectins, the dimeric Oriza sativa agglutinin (OSA) and the monomeric Urtica dioica agglutinin (UDA), were also tested but at a concentration of 0.1 % w/v exhibited no significant antimetabolic effect towards BPH, although the related lectin wheatgerm agglutinin (WGA) has previously been demonstrated to be toxic towards the insect