Dietary proteinase inhibitors alter complement of midgut proteases

Abstract

Plant serine proteinase inhibitors (Pls) have the potential to restrict the growth and/or development of herbivorous insects. However, there are limitations to the efficacy of these Pls. An insect's susceptibility to a Pl is determined, at least in part, by the relative proportion of proteolytic enzyme activity in the midgut that is suppressed by that inhibitor. Insects adapt to dietary trypsin inhibitor in their host plant by secreting “inhibitor-resistant” trypsin(s). These “inhibitor-resistant” enzyme(s) may be the standard proteinase(s) secreted into the midgut (e.g., Pieris rapae), or may be enhanced following ingestion of proteinase inhibitor (e.g., Helicoverpa zea). In addition, insects may be pre-adapted to specific Pl(s), following adaptation to a Pl from the same family. For example, Pieris rapae is a crucifer specialist that is resistant to cabbage Pl, but is also resistant to Kunitz soybean trypsin inhibitor, a Pl in the same family as cabbage Pl, but from a non-host plant. The ultimate value of this pre-adaptation to herbivory by a species of insect will be determined by the number of different families of Pl in host plant(s) to which the species has adapted, and the distribution of those families among other species of plants. Thus, it is possible that the presence of a plant Pl limits herbivory by insect(s). However, multiple inhibitors, matched to the complement of enzymes in the insect's midgut, may be required to enhance this resistance of plants to herbivorous insects. © 1996 Wiley-Liss, Inc.