Oilseed rape is an important crop in Europe. Many insect pests, mainly Coleoptera, feed on various parts of this plant at different cultural stages. Creation of genotypes more resistant to these pests via the expression of entomopathogenic proteins in transgenic plants could reduce the need for chemical control. We thus investigated a new crop protection strategy based on the expression of proteinase inhibitors (PI) in transgenic oilseed rape to limit attacks by coleopteran pests. A serine PI (CII from soybean) and a cysteine PI (OCI from rice), able to inhibit the corresponding proteolytic activities of these coleoptera in vitro, were introduced via Agrobacterium in a spring genotype. The expression level of the introduced PIs was determined and homozygous plants were obtained. The impact of ingestion of OCI or/and CII expressed in transgenic plants was evaluated on growth, development and mortality of four pests feeding on oilseed rape (Baris, cabbage stem flea beetle, rape stem weevil and cabbage seed weevil). Although there were no marked deleterious effects on the tested insects, various reactions were observed at the gut proteinase level. The results are discussed along with prospects for improving pest resistance in oilseed rape. Moreover, since this plant is highly attractive to pollinating insects, possible deleterious effects on honeybees were assessed. Honeybees mainly possess serine gut proteinases, and in vitro feeding bioassays allowed us to determine a threshold dose (50-100 mug/g pollen) of a serine PI, beyond which negative effects were observed. Consumption of high doses of this PI (much higher than those produced in leaves) induced protease overproduction. However, oilseed rape expressing serine PI, under control of the CaMV 35S promoter, does not threaten honeybees, since the transgene is not expressed in pollen and nectar.
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