Toxic Action of Plant Extracts on Some Pests of Economic Importance

1 Plant Protection Institute, BG-2230 Kostinbrod, Bulgaria
2 Institute of Agriculture, BG-2500 Kyustendil, Bulgaria


VELCHEVA, N., N. ATANASSOV, V. VELCHEV, R. VULCHEVA, O. KARADJOVA and M. VELICHKOVA, 2001. Toxic action of plant extracts on some pests of economic importance. Bulg. J. Agric. Sci., 7: 133-139

The insecticidal activity of wild geranium – Geranium macrorrhizum L. (Geraniaceae); milkweed – Euphorbia cyparissias L. (Euphorbiacea); and milk thistle – Silybum marianum L. (Asteraceae) was tested against various agricultural pests: – the green peach-potato aphid – Myzus persicae Sulz (Homoptera, Aphididae); the greenhouse whitefly – Trialeurodes vaporariorum West (Homoptera, Aleurodidae), the codling moth – Laspeyresia pomonella L. (Lepidoptera, Tortricidae); the cabbage moth – Mamestra brassicae L (Noctuidae, Lepidoptera) and the two-spotted spider mite – Tetranychus urticae Koch. (Acarina, Tetranychidae). The standard bioassay was applied to investigate the ovicidal, the larvicidal, and the repellent activity of the three Bulgarian plant species. Tests were made on the water and ethanol extracts from leaves and stems of G. macrorrhizum and of E.cyparissias, and on the waste product of the seeds of S. marianum.
The aphicidal effect of G. macrorrhizum was established for the first time. The efficacy of 1% G. macrorrhizum extract against M. persicae on the seventh day after treatment was above 95%. The extracts from G. macrorrhizum had an ovicidal activity to the codling moth, causing mortality mainly to the embryos in the late stages of development. The efficacy of wild geranium extracts against T. vaporariorum eggs and larvae was insufficiant (12-17%).
The extracts from G. macrorrhizum and E. cyparissias had the highest larvicidal activity against L. pomonella.
The insecticidal property of the ethanol extracts from pharmaceutical waste products obtained from the seed of S. marianum was established for the first time. The highest efficacy (100%) was estabished against T. vaporariorum larvae, and against M. persicae (adults and larvae).
G. macrorrhizum and E. cyparissias plants synthesize substances with strong activities against T. urticae (above 90%). These extracts reduced considerably the density of the treated mite population on the third day post treatment.
All tested extracts exhibited no ovicidal and larvicidal effect on the M. brassicae.

Key words: plant extracts, ovicidal, larvicidal and repellent effect