Binding of garlic (Allium sativum) leaf lectin to the gut receptors of homopteran pests is correlated to its insecticidal activity

The homopteran insect pests sometimes cause serious damage to many crop plants. Unfortunately this particular class of insects can not be controlled by Bacillus thuringiensis insect control protein or any other established insect control agent. However, purified garlic leaf lectin (ASAL), a 12 kDa dimeric mannose binding protein has been found to have detrimental effect on growth and survival of two important homopteran insect pests, Lypaphis erysimi, commonly known as aphids and Dysdercus cingulatus (red cotton bug). The insecticidal activity of ASAL towards these insects has been monitored through insect bioassay using synthetic medium and the respective LC50 values for both the insects have been determined. The unique binding ability of ASAL to the inner epithelial membrane of the affected insect gut has been demonstrated through immunohistochemical analysis. The receptor proteins of the gut epithelial cells responsible for the specific binding characteristics have also been identified through Western analysis. The ligand-binding ability of this lectin, correlated with the insecticidal property, facilitated to ascertain the mode of action of the particular lectin on above mentioned insects physiology. This also gives an indication that garlic leaf lectin remains stable even in the insect gut environment. These findings open up the possibility of using garlic leaf lectin as a potent control agent to engineer crop plants for insect resistance. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.