Does host range influence susceptibility of herbivorous insects to non‐host plant proteinase inhibitors?

Abstract

AbstractWe examined the influence of proteinase inhibitors on digestive enzymes and development of oriental beetle, Exomala orientalis Waterhouse, European chafer, Rhizotrogus majalis (Razoumowsky), Phyllophaga white grub, Phyllophaga anxia (LeConte), cranberry root grub, Lichnanthe vulpina (Hentz), Japanese beetle, Popillia japonica Newman, Asiatic garden beetle, Maladera castanea (Arrow) (Coleoptera: Scarabaeidae), and the black cutworm, Agrotis ipsilon (Rottemburg) (Lepidoptera: Noctuidae). We demonstrated that all species within our test group had alkaline midguts that contained proteinase activity that could be inhibited, in vitro with serine proteinase inhibitors. Our data suggests that host range may influence the susceptibility to non‐host inhibitors. Chronic ingestion of the serine proteinase inhibitor, Kunitz‐soybean trypsin inhibitor (STI), significantly reduced proteolytic activity in vivo in those species with relatively specialized feeding habits (i.e., cranberry root grub, Japanese beetle, Asiatic garden beetle, and black cutworm). Chronic ingestion of STI also resulted in reduced larval growth and delayed pupation for black cutworm, and elevated larval mortality for Japanese beetle. However, chronic ingestion of STI did not influence larval survival for those species with relatively generalized feeding habits (i.e., oriental beetle, European chafer). Based on these results, we propose mechanistically‐based criteria for selecting proteinase inhibitors for phytochemical defense against herbivorous insects.