Bio-insecticidal activity of three essential oils against Rhyzopertha dominica (Fabricius, 1792) (Coleoptera: Bostrichidae)

Natural plant extracts, especially essential oils, are used largely against plant pests. The aim of this study was to investigate the bio-insecticidal effect of chemical extracts of three plants, Mentha palegium I,. (Lamiales: Lamiaccae), Lavandula stoechas L. (Lamiales: Lamiaceae) and Rota chalepensis I.. (Sapindales: Rutaceae) collected from Tunisia, on the lesser grain borer Rhyzopertha dominica (Fabricius, 1792) (Coleoptera: Bostrichidae), which is a primary pest of stored wheat. To reach this goal, we firstly did bio-assays to test the toxicity of these plant extracts on R. dominica adults using different concentrations of plant extracts on wheat seeds. Secondly, we analysed the chemical compounds of these plant extracts using GC-MS and GC-FID. Our results demonstrated that R. dominicfc mortality was significantly higher with increasing plant essential oils concentrations (CL95 values 45.68, 11312 and 170.52 mu l/l((air)) for M. pules/am, R. chalepensis and L. stoechas, respectively. The main chemical compounds identified of M. pulegium oils were: pulegone (76.9 %), isomenthone (12.0 %) and limonene (1.73 %), whereas those from L. stoechas were: camphor (23.8 %), 1,8-cineole (17.8 %) and camphene (7.69 %). Rula chalepensis oil revealed high contents of imdecanone (51.2 %), 2-nonanone (39.16 %) and 2-decanone (2.32 %). Our results also showed that M. pulegium essential oil has a significant effect against R. dominicfc with LC50 value of 13.51 mu l/l((air)) compared to R. chalepensis and L. stoechas corresponding to 39.11 and 42.9 mu l/l((air)), respectively.