The effect of plant protein quality on insect digestive physiology and the toxicity of plant proteinase inhibitors

We examined the influence of protein quality on the growth of larval Spodoptera exigua (Hübner) and on the toxicity of soybean trypsin inhibitor to these larvae. Using artificial diets containing the test proteins (either soy, tomato foliar protein, gluten, zein or casein) we were able to show that (1) protein quality significantly influences the growth of larval S. exigua, (2) protein quality does not significantly effect the level of tryptic activity in the larval gut, (3) protein quality significantly alters the toxicity of soybean trypsin inhibitor to the larvae (i.e. the more nutrituous the protein, the less toxic the inhibitor), and (4) the aspect of protein quality that most significantly influences its effect on larval growth is the amino acid profile (particularly the lysine + arginine content).