Antinutritive and toxic components of plant defense against insects

Chemical defense of the tomato plant against noctuid larvae is argued to result from suites of interactive chemical traits that simultaneously impair the acquisition of nutrients and toxify the insect. Defense results from tomatine, catecholic phenolics and phenol oxidases, proteinase inhibitors, and lipoxygenase. The catalytic role of plant oxidative enzymes in activating a variety of defense mechanisms is discussed. It is argued that the terms “digestibility reducer,” “toxin,” and “nutrient” signify ecological outcomes, not properties of molecules. Current views on the roles and the modes of activity of plant natural products against herbivorous insects are challenged. It is proposed that chemical context and mixture are critical determinants of biological activity, and that viewing natural products as isolated defensive factors is often misleading. © 1996 Wiley-Liss, Inc.