A FEEDING DETERRENT FOR THRIPS-PALMI KARNY (THYSANOPTERA, THRIPIDAE) FOUND IN TOMATO LEAVES - ISOLATION AND IDENTIFICATION

Despite its polyphagous nature, Thrips palmi does not really attack tomato plants. In efforts to elucidate the chemical basis responsible for the tomato's resistance, a crystalline compound possessing strong antifeeding activity for this insect species was isolated from tomato leaves by means of methanol extraction, water/butanol partition, silica gel chromatography, and preparative high-performance liquid chromatography. According to responses to certain test reagents, qualitative and quantitative LC profiles of component sugars, melting point, specific rotation, UV-, IR-, MS-, H-1-NMR- and C-13-NMR-spectra, the compound was identified as alpha-tomatine, a known steroidal glycoalkaloid in tomato plants. The immunity of tomato plants to T. palmi is explained solely by the occurrence of alpha-tomatine, because T. palmi does not use airborne information (attractants/repellents) to avoid tomato leaves, and tomato leaves apparently provide the required phagostimulants and nutrients.