One form of natural defense of plants against insects is mediated by proteinase inhibitors. The inhibitors are thought to have coevolved with insect herbivory, and to function by blocking the digestive proteases in the larval gut, thereby limiting the release of amino acids from food protein. As a consequence, the larvae are arrested in development, and eventually die. Genes encoding protease inhibitors have been used to produce resistant transgenic plants as a crop-protection strategy. In a former study, we showed the influence of Kunitz-type inhibitors from D. mollis (Leguminosae-Mimosoideae) seeds on digestive enzyme properties and development A. kuehniella and C. cephalonica larvae, two Lepidoptera insects.
       Incubation with whole midgut extracts of  A. kuehniella or C. cephalonica for up to 6 h at 37 °C had no effect on DMTI or DMTI-II, the larval proteases were unable to digest the inhibitors. The larval trypsin-like activity was also determined by incubating a mixture of midgut extract with different concentrations of inhibitors for 15 min at 37 °C. Increasing concentrations of inhibitors progressively decreased the trypsin-like activity. Neither DMTI nor DMTI-II, when incorporated into artificial diet at 2%, were active as insecticide agents against these two species. The results suggest that insects were able to physiologically adapt to inhibitors by altering the digestive proteolytic activity.
       Nevertheless, this study does not discard the use of inhibitors from D. mollis in plant biotechnology against other species of insects; they just help us to understand how they work as biological agents.
       Supported by: CNPq, FUNDECT, FINEP, and CAPES