Over the last few years, several plant lectins have been studied for their effects on higher animals and insects, but still the working mechanism of these plant defence proteins remains enigmatic. In some cases it was seen that the eventual discomfort caused by lectins is so severe that experimental animals refuse to continue eating a lectin-containing diet. The latter phenomenon may be indicative of a repellent effect of lectins. In this research we have investigated the anti-insect effect of garlic (Allium sativum) leaf (ASAL) and bulb (ASAII) lectins that are expressed in tobacco plants. In choice feeding experiments, caterpillars of the cotton leafworm Spodoptera littoralis were exposed to combinations of leaves of transgenic tobacco plants expressing ASAL or ASAII, and wild type tobacco plants. The distribution of the caterpillars over the different leaves as well as the leaf damage were scored for different larval stages. Our results show that ASAL-expressing tobacco plants possessed the strongest anti-insect activity. These first results are evaluated in relation to the level of lectin expression in the tobacco plants, and potential mechanisms are discussed.
