Is oilseed rape specific glucosinolates content a key cue for larval infestation of Psylliodes chrysocephala in field conditions?
Résumé
The cabbage stem flea beetle (CSFB - Psylliodes chrysocephala) is among the main pests in winter oilseed rape (OSR - Brassica napus) across Europe. Specific glucosinolates compounds found mainly in Brassicacea plants are feeding stimulant for the CSFB specialist insect and have an impact on their larval development. However, it remains unclear if glucosinolates profile (GP) is a key cue for females’ host acceptance to lay their eggs in proximity of a chosen plant. Increasing evidences of the reduction of CSFB attacks by OSR-mixed cropping systems were provided in recent years. The impact of genetic variability and companion plant on OSR’s GP and its possible implication in CSFB host acceptance were investigated. Three OSR varieties were grown in microplots with or without Fababeans intercropping, in a field trial with four replicates. GP of leaves from three samples per microplots were analyzed before CSFB infestation and Berlese traps were done on the sampled plants in winter to evaluate the number of larvae. The number of larvae per plant was positively correlated with the concentration of Glucoraphanin and of Butyl-glucosinolate and negatively correlated with Glucobrassicanapin’s concentration. The varietal factor was the main driver of the variability in GP among the surveyed plants. Mixed cropping had an effect on some specific glucosinolates concentration and its effect was variety- dependent. However, only the genetic factor had a significant influence on the OSR infestation. We brought evidence of the impact of specific glucosinolates on host acceptance of CSFB in field conditions and its variability among OSR cultivars.