RESUMO
Ageratum houstonianum, commonly called as bluemink or flossflower, is a predominant weed growing widely in the western Himalaya region. Here, we studied its chemical composition of essential oil (EO), characterization of pure compounds, screening of EO, fractions and pure compounds for their insecticidal activities against larvae of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) and aphid, Aphis craccivora Koch (Hemiptera :Aphididae).The volatile composition of the EO from above ground parts of A. houstonianum was extracted by steam distillation and characterized by GC and GC–MS analysis. Precocene II (42.16%), precocene I (18.65%) and beta–caryophyllene (15.56%) were the main constituents. Fatty acid composition of the plant was determined using GC–MS after derivatization. The compounds ageratochrome and 1–heptadecene were isolated and characterized using Mass, 1H and 13C NMR spectroscopy. EO, hexane/methanol fractions and isolated compounds were tested against P. xylostella and A. craccivora. Results indicated that EO, hexane fraction, ageratochrome and 1–heptadecene showed more toxicity to larvae of P. xylostella (LC50=2.82, 4.91, 2.15, 4.86 mg/mL, respectively); whereas methanol fraction was more effective against A. craccivora (LC50=1.11 mg/mL) in the residual toxicity assay. The EO also showed repellent activity to P. xylostella (RC50 =2.25 mg/mL).