HIGH-LEVEL OF RESISTANCE TO PROTEINASE-INHIBITORS MAY BE CONFERRED BYPROTEOLYTIC CLEAVAGE IN BEETLE LARVAE

Incorporation of genes encoding proteinase inhibitors into oilseed rap e genome could confer resistance to Coleoptera, which are the major pe sts on rape in Europe. A detailed study of the digestive proteinase of a model cruciferous-feeding Coleoptera, Phaedon cochleariae, showed t hat this insect relies on a complex proteolytic system including serin e, cysteine, aspartyl proteinases, and leucine aminopeptidases. The in hibition of general and specific activities by a range of proteinase i nhibitors in vitro suggested that oryzacystatin I (OCI) and Bowman-Bir k inhibitor (BBI) would have adverse effects when ingested by the larv ae. However, the growth and the feeding of larvae reared on oilseed ra pe leaf discs treated with a high dose of OCI and/or BBI were not affe cted. Moreover, the levels and patterns of proteolytic activities were not modified in these larvae. The study of the interactions between P . cochleariae larval proteinases and OCI and BBI revealed that both in hibitors were rapidly cleaved by serine proteinases in association wit h leucine aminopeptidases, and consequently lost their inhibitory capa city. This mechanism of resistance is very efficient, and may be wides pread among Coleoptera. The major implications for insect control usin g proteinase inhibitor-based strategies are discussed. (C) 1998 Elsevi er Science Ltd. All rights reserved.