Natural products as sources of environmentally safer pest control agents.

摘要

Bioassay-guided fractionation of organic crude extracts of acorns obtained from live oak trees (Quercus virginiana) and flowers (pink and red) from Oleander plants (Oleander nerium) resulted in the isolation of bioactive fractions. The organic crude extracts were subjected to thin layer chromatography (TLC) and column chromatography (CC). The fractionation of the organic crude extracts yielded various fractions that were grouped together and the Infrared (IR) and 1H and 13C Nuclear Magnetic Resonance (NMR) survey spectra of the most bioactive fractions were acquired.;Various concentrations of the organic crude extracts from acorns and oleander flowers (100ppm, 200ppm, 500ppm and 1000ppm) were tested against the brine shrimps and the acute (6h exposure) and chronic (24h and 48h exposure) median lethal dose (LD50) values were determined. The estimated LD50 values indicated that the brine shrimps showed both dose and time dependent responses. The crude extracts showed strongest chronic toxicity toward the brine shrimps at 48h. The fractions obtained from purification of the organic crude extracts (concentration = 1000ppm) were also tested against brine shrimps (Artemia salina) and specifically against houseflies (Musca domestica) and nematodes (Rhabditis and Cephalobus species). The pest control activities of the isolated fractions were evaluated.;The isolated fractions from the organic crude extracts showed varied pesticidal activities against the brine shrimps, houseflies and nematodes. The acorn shell and nut and oleander flower fractions showed activities ranging from 67.0% to 100% against the brine shrimps after exposure to 1000ppm concentration for 48 h. Some of the fractions (1000ppm) showed very strong insecticidal activities toward houseflies and nematicidal activities toward nematodes while others showed low or no pesticidal activity. The Hexane:Acetone (90%:10%) fraction of the acorn nut showed the highest insecticidal activity (97.5% mortality rate) after 24h. The Hexane:Acetone (90%:10%) fraction of the acorn shell (100% mortality rate) and the Hexane (100%) fraction of the acorn nut (100% mortality rate) showed the strongest nematicidal activities against the rhabditis nematode species after 24h. These fractions however had very low effects on the cephalobus species. The bioactive fractions showed specificity in their activities against the houseflies and nematodes.