Fumigant and Contact Toxicity of Ruta Chalepensis L. (Rutaceae) Essential Oil Against Five Coleopteran Stored Product Pests and Its Effects On Cholinesterases

The essential oil composition of aerial parts of Ruta chalepensis L. was analyzed with GC-MS. Seventy-nine compounds were detected representing 85.93 ± 1.08% (n = 3) of the essential oil. The major components of the essential oil were 2-undecanone 21.52±0.21%, 2-nonanone 18.31 ± 0.27%, and 2-nonyl acetate 13.22%. The highest insecticidal contact toxicity of the oil was observed against Rhyzopertha dominica F. with 0.018 μL/insect LD50 and 0.039 μL/insect LD90 after 24h. Essential oil also produced considerably low 0.50 and 0.59 μL/insect LD50 values after 24h against Sitophilus oryzae L. and Sitophilus granarius L. respectively. The lowest contact toxicity was observed against Tribolium castaneum Herbst. and Tribolium confusum Jacquelin du Val. 0.138 and 0.078 μL/insect LD50 after 24h respectively. The highest fumigant toxicity was observed against S. granarius for the application concentration of 10 μL, 10% oil/acetone (v:v) in a 10 mL chamber which afforded 100.00 ± 0.00 % mortality after 48h. The essential oil also produced high fumigant toxicity against S. oryzae, T. castaneum, and R. dominica which were 95.47 ± 3.41%, 93.30±5.54%, and 85.47 ± 3.41% mortality at 20 μL application concentration of the oil solution after 48h. The R. chalepensis essential oil produced low acetylcholinesterase enzyme 5.29 ± 1.20% (n=3) inhibition and mediocre butyrylcholinesterase enzyme inhibition 42.6 ± 0.71% (n=3). According to the insecticidal activity assays performed, R. chalepensis essential oil seems to be a promising source that could yield natural compounds that could be employed in stored product pest management.