1Laboratoire de Neurobiologie Comparée des Invertébrés, INRA, BP 23, 91190 Bures-sur-Yvette, France.
2Laboratoire de Biologie Cellulaire, INRA, Route de St Cyr, 78 026 Versailles Cedex, France.
Transgenic plants expressing proteinase inhibitors (PIs) to confer insect resistance is a new strategy under study for crop protection. To evaluate this strategy, the impact of such plants on non target insects is to be assessed. Honeybees being the major pollinating insect of many crops, we designed experiments to investigate the effect of proteins inhibiting the digestive processes of insects. The proteins were delivered at doses reallistic with those found in plants and at higher concentrations (10 to 100 times higher). First, the toxicity of PIs-added sugar solutions was evaluated on caged bees. Diets containing the highest concentration (1mg/ml) of PIs significantly increased the probability of death at a given time along their lifespan. Second, sublethal effects on the olfactory learning abilities were investigated on individual restrained bees. No effect was found after short-term exposure, whereas prior ingestion of some proteins at the highest dose significantly reduced the level of conditioned response to odour. Third, whole colonies were fed with a low concentration (6 µg/ml) of one PI during 2 months. Along the exposure period, the amount of protein residues in the food stored in the hive and in the bees was measured, the colony state was checked and the subsequent learning performances of foragers were tested. No drastic effects was found on any of these parameters. These experiments could be included in regulatory procedures for risk assessment of genetically modified crops.