Chemical profile, mosquitocidal, and biochemical effects of essential oil and major components of Dysphania ambrosioides against Culex quinquefasciatus Say

To seek new mosquito control agents while avoiding the environmental impacts and toxicity hazards of conventional pesticides, the essential oil of Dysphania ambrosioides was obtained by hydrodistillation and analysed using GC-FID and GC-MS. The compounds 1-methyl-4-(1-methylethyl)-2,3-dioxabicyclo[2.2.2]oct-5-ene (cis-ascaridole), 1-methyl-4-(1-methylethyl) benzene (p-cymene), and 1-isopropyl-4-methyl-1,3-cyclohexadiene (p-mentha-1,3-diene also known as alpha-terpinene) were identified as the major components. The EO and the major fractions showed remarkable mosquitocidal activity against third in star larvae and adults of Culex quinquefasciatus Say. The oil and fractions were assayed at 3.125, 6.25, 12.5, 25, and 50 mu l/l. Mortality was time- and dose-dependent. At 24 h post-exposure at an assayed concentration of 50 mu l/l, the larval and adult mortalities ranged between 80.11-100% and 91.22-100%, respectively. Strong larvicidal and adulticidal activities were recorded in the cases of the crude oil and cis-ascaridole. The LC50 values after 24 h of treatment ranged between 6.2-20.1 mu l/l and 5.1-13.9 mu l/l against larvae and adults, respectively. The corrected percentage mortalities increased over time with the tested plant oil and the major fractions relative to the control. The time required to achieve 50% mortality (LT50) decreased remarkably with all treatments. The tested EO and major fractions effectively inhibited larval acetylcholinesterase activity with IC50 values ranging from 8.44 to 64.80 mM compared with 2.08 x 10(-3) mM for the reference standard, methomy. The results indicate the potential of developing natural mosquitocides against C. quinquefasciatus based on the tested EO and its major fractions.