Selected Proteinase Inhibitor Effects on Alfalfa Weevil (Coleoptera: Curculionidae) Growth and Development

Abstract

Proteinase inhibitors, which can inhibit digestive enzymes of specific insects, are a potential alternate control mechanism against herbivorous insects. An in vivo laboratory bioassay was developed to screen proteinase inhibitors for their ability to inhibit growth and development of the alfalfa weevil, Hypera postica (Gyllenhal). Larval foliar feeding, pupation, and adult emergence were significantly decreased by E-64, pHMB, and leupeptin, inhibitors of cysteine proteinases, at a concentration of 0.1%. Aspartic proteinase inhibitors (antipain and pepstatin) demonstrated mixed results at 0.1 and 0.5% concentrations. Serine proteinase (trypsin) inhibitors had no effect on any of the variables measured at 0.5%. These observations suggest that alfalfa weevil larvae use cysteine proteinases as major digestive enzymes and that other proteinases may be present as well. In vivo studies on the effects of proteinase inhibitors on herbivorous insects, in most cases, have been determined by measuring larval development (weight) and mortality. This study reports on the negative effects of specific proteinase inhibitors on insect larval foliar feeding, pupation, and adult emergence when ingested with an insect℉s preferred host.