Essential oil and polyacetylenes from Artemisia ordosica and their bioactivities against Tribolium castaneum Herbst (Coleoptera: Tenebrionidae)

Abstract

Five polyacetylenes (1-5) were isolated from Artemisia ordosica, one of the main arido-active shrubs growing in the arid areas in China. Their molecular structures were identified with NMR spectroscopy. The compounds were confirmed as capillene, capillin, capillinol, cis-dehydromatricaria ester and trans-dehydromatricaria ester. It was found that three compounds (1-3) had similiar structural skeleton of 2,4-hexadiyn-1-ylbenzene. The repellent and fumigant activities against Tribolium castaneum adults were investigated for compounds isolated and the essential oil. Bioassays showed that the essential oil extracted from the aerial parts of A. ordosica possessed fumigant toxicity of LC50=18.65mg/L air, and compounds (1-4) had stronger activities from LC50=4.06mg/L air to 6.16mg/L air against T. castaneum adults. At the tested concentrations (62.91 and 12.58nL/cm2), the crude essential oil and compounds (1, 2 and 4) showed the same repellent activity (p>0.05) with DEET against T. castaneum adults at both 2h and 4h after exposure. Compound 2 showed strong repellence (PR=100%) at tested concentrations of 62.91, 12.58 and 2.52nL/cm2 at 2h after exposure. Moreover, at tested concentration (62.91, 12.58, 2.52 and 0.5nL/cm2), the PR value of compound 4 was all higher than 90% at both 2h and 4h after exposure. The results showed that the crude essential oil and the isolated polyacetylenes possessed fair repellent and fumigant activities. Furthermore, potential relationships between structure and bioactivity were also discussed. It might be found that the existence of acetylenic bonds was the principal factor of fumigant activity, and with the increase of acetylenic bonds, the fumigant activity would enhance. In addition, it was believed that oxygenous groups connected to the acetylenic bonds might contribute to fumigant toxicity against T. castaneum adults.