Lectins are carbohydrate-binding proteins present in plants that are considered to play a role in plant-insect relationships for controlling herbivory insects. In addition recent progress in plant transformation has increased the interest in plant lectins to be used as tools in the control of important pest insects. However as the amounts of lectins are small there is need for miniature tools to screen for insecticidal potency. This paper describes a routine test for screening the toxicity of small amounts of plant lectins against the pea aphid Acyrthosiphon pisum. This aphid is of economic importance as it attacks a wide range of legumes including many important forage and vegetable crops, and in addition it is transmitting plant pathogenic viruses. As case study we tested here the insecticidal potency of the mannose-binding Galanthus nivalis (snowdrop) agglutinin (GNA). A liquid artificial diet was prepared containing essential amino acids, vitamins, minerals and 30% sucrose, and 230 µl was provided as food in a parafilm sachet on an in-house constructed cylindric plexiglass cage. The current design allowed us to test < 2mg of GNA to be mixed into the artificial diet preparing six concentrations ranging from 50 up to 1200 µg/ml. In each cage 20 neonate aphids were placed and followed for survival during 3 days; four replicates were tested per concentration. Using sigmoidal curve fitting, the LC50 for GNA was estimated 389 µg/ml (95% CL: 341-444). In summary the results show a strong acute toxicity of GNA lectin against A. pisum aphids.
