Volatile, nonvolatile composition and biological activities of Ageratum houstonianum Mill. against diamondback moth, Plutella xylostella (L.) and aphid, Aphis craccivora Koch

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).

Seasonal incidence of black scale, Saissetia oleae (Olivier) on the fern, Thelypteris tylodes (Kunze) from western Himalaya

Incidence of insect pests on ferns, particularly sap suckers, needs attention as it causes more damage indirectly. Here, we recorded seasonal incidence of black scale, Saissetia oleae (Olivier) on Thelypteris tylodes (Kunze) (Thelypteridaceae) for a period of one year from May 2012 to April 2013 at weekly interval. Results have shown that incidence of S. oleae first occurs in the first week of May 2012 (5.4 scales/rachis).The infestation increases gradually from second week of May (6.6 scales/rachis) and attains its peak during the last week of July 2012 (27.8 scales/rachis) due to high temperature (20–27°) and relative humidity (74-83%). The infestation starts declining gradually from August 2012 to November 2012 (24.7 scales/rachis to 3.4 scales/rachis). The lowest scale incidence was observed during the last week of December 2012 (0.50 scales/ rachis) and second week of January 2013 (0.2 scales/rachis). The scale infestation was not observed from third week of January 2013 to entire March 2013. The incidences of scale infestation during the period of observation have shown to be significant linear positive correlation with temperature, relative humidity and rainfall.