Toxicity and repellence of Citrus jambhiri Lush rind essential oil against maize weevil (Sitophilus zeamais Motschulsky 1855) (Coleoptera: Curculionidae)

Rind of matured fruits of Citrus jambhiri Lush was hydro-distilled to obtain essential oil (EO) which was subjected to Gas chromatography-Mass spectrometry (GC-MS) analysis. The EO was evaluated for fumigant toxicity (at 27- 107µL/L air) and repellence against maize weevil (Sitophilus zeamais Motschulsky). Area preference methodology was used to evaluate the repellence of the EO at 0.15-0.9 µL/cm2, while isopropanol served as control for both bioassays. The experiments were set up in a completely randomized design and data were subjected to analysis of variance and probit analysis. Fifty-two compounds were identified in the EO with the predominant compounds being a-terpineol (8.03%), citral (7.00%), 4-terpineol (6.52%), caryophellene (4.58%), cis-geraniol (4.44%), citronellal (4.38%), ß-bisabolene (4.01%) and n-hexadecanoic acid (4.70%). Others were a- bergamotene (3.74%), lemonol (3.23%), precocene I (3.33%) and ß-copaene (3.09%). Toxicity progressed with EO dose and exposure period and application of EO at 80 and 107µL/L air caused significantly higher mortality (33.75-100.00%) than isopropanol (0.00-22.50%). Lethal time for 50% assayed weevil (LT50) for the EO application at 107 µL/L air {7.51 (6.95-8.13) h} was significantly lower than the values obtained for 27 and 53 µL/L air {44.78 (27.49-312.61) and 21.87 (11.91-45.96) h, respectively}. EO caused significantly higher repellence (75.00-90.00%) than control (15.00%) at 24 hours after treatment. The results indicate that C. jambhiri rind EO has prospects as effective biorational formulation for control of maize weevil.