Changes in midgut endopeptidase activity of Spodoptera frugiperda (Lepidoptera : Noctuidae) are responsible for adaptation to soybean proteinase inhibitors

The development of transgenic maize plants expressing soybean proteinase in hibitors could reduce the economic damage of one of the major maize pests i n Brazil, the fall armyworm, Spodoptera frugiperda (J.E. Smith, 1797). We e xamined the influence of soybean proteinase inhibitors on digestive enzyme properties and development of S. frugiperda larvae. The inhibition of tryps in and chymotrypsin activities in vitro by soybean proteinase inhibitors su ggested that either Kunitz (SBTI) or Bowman-Birk (SBBI) would have a potent ial antimetabolic effect when ingested by insect larvae. However, chronic i ngestion of semipurified soybean inhibitors did not result in a significant reduction of growth and development of fall armyworm. Therefore, digestive serine proteinase activities (trypsin and chymotrypsin) of fall armyworm l arvae were characterized, The results suggest that S. frugiperda was able t o physiologically adapt to dietary proteinase inhibitors by altering the co mplement of proteolytic enzymes in the insect midguts.