Toxicity of Leaf Extracts of Ageratum conyzoides to Lepidoptera Pests of Horticultural Crops

Abstract

ABSTRACT The insecticidal activity of the hexane and alcohol extracts of the plants Ocimum selloi B., Ruta graveolens L., Leonotis nepetaefolia L., Datura stramonium L., Cordia verbenaceae L., Mentha piperita L., Mormodica charantia L. and Ageratum conyzoides L. were tested against larvae of Diaphania hyalinata (L.) (Lepidoptera: Pyralidae). Among these, the extract of only A. conyzoides showed biological activity. The hexane extract of this plant species was therefore successively fractionated by silica gel column chromatography for isolation and purification of the active chemical constituents. The insecticidal activity of the fractions and compounds were monitored through bioassays with larvae of D. hyalinata (L.), Dione juno juno (Cr.) (Lepidoptera: Nymphalidae) and Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). The compounds 5,6,7,8,3′,4′,5′-heptamethoxyflavone; 5,6,7,8,3′-pentamethoxy-4′,5′-methylenedioxyflavone and coumarin were identified as the active compounds in the fractions. The increasing order of susceptibility to coumarin was D. hyalinata < D. juno juno < T. absoluta. The increasing order of toxicity to D. juno juno was 5,6,7,8,3′-pentamethoxy- 4′,5′-methylenedioxyflavone < coumarin < 5,6,7,8,3′,4′,5′-heptamethoxyflavone.