INDISCRIMINATION OF MANDUCA-SEXTA LARVAE TO OVEREXPRESSED AND UNDEREXPRESSED LEVELS OF PHENYLALANINE AMMONIA-LYASE IN TOBACCO-LEAVES

Manduca sexta (L.) larvae were unable to discriminate between transgen ic tobacco leaves expressing high or low levels of phenylalanine ammon ia-lyase (PAL) in dual choice arenas. Tobacco leaves overexpressing PA L had up to ten times more chlorogenic acid and up to twice as much ru tin in their leaves than leaves containing the same sense-suppressed g ene. Caterpillars reared previously on artificial diet or tobacco leav es had no preference for either leaves over-or underexpressing PAL. Ap plication of exogenous chlorogenic acid to PAL-suppressed leaves at le vels similar to the overexpressed leaves did not affect M. sexta's cho ice. When applied at higher rates, treated leaves were preferred by ca terpillars reared on tobacco leaves but not by diet-reared larvae. Our results with leaves confirm earlier studies with M. sexta using simpl er substrates and mixtures of test compounds and provides further evid ence that leaf phenolics, such as chlorogenic acid, do not act as feed ing deterrents for larval M. sexta.