Oil composition of sweet flag (Acorus calamus) and its toxicity against the maize weevil

Abstract

Essential oil of Acorus calamus L. rhizome from Daman, Makwanpur, Nepal was extracted using Clevenger-type hydro-distillation apparatus and toxicity to Sitophilus zeamais was evaluated. Further, chemical constituents of essential oil were also analyzed by GC-mass spectrometer. The major chemical constituents identified were of β-asarone (79.7%), Methyl isoeugenol (4.08%), Dehydroxy-isocalmendiol (4.03%), Shyobunone (3.27%), (0.93%), δ-Cadinene (0.85%), Epishyobunone (0.68%), and Isoshyobunone (0.47%). For the weevils, when released in methanol diluted sweet flag essential oil treated scintillating vial, LC₅₀ at 24, 48, and 72 hrs were estimated to be 1.23 (y=2.21x-0.22), 0.45 (y=1.68x+0.58) and 0.17 (y=2.98x+2.29) percent concentration of oil respectively. Hundred percent weevil mortality was obtained within 24 hours with 10% concentration while it took more than 120 hrs. with 0.16 % concentration. Essential oil of potential plant could be one of the good alternatives to chemical pesticides in managing storage pests. Essential oil of sweet flag rhizome can be further tested in field and storage pests. MRL should be ascertained to allowable limits as β-asarone has carcinogenic effect at certain level.