A study on contact toxicity of extracts from Polygonum orientale against 13 species of agricultural pests.

Contact toxicity of extracts from Polygonum orientale against agricultural pests have seldom been researched.A study on contact toxicity of the extracts can provide a theoretical basis for formulating new types of botanical insecticide.Contact toxicity of the extracts against pests was carried out by the immersion method.Ethyl acetate extract from seeds of P.orientale had very strong contact toxicity against 4th or 5th instar larvae of Mythimna separate,Pieris rapae,Helicoverpa armigera,Mamestra brassicae,Spodoptera exigua and Agrotis ypsilon.Percentages of corrected mortality were between 87.5% and 100% when the concentration of the fraction was 16.80 g/L.The fraction also had very strong contact toxicity against 3rd instar larvae of Plutella xylostella,with a corrected mortality of 92.85% when the concentration of the fraction was 21.00 g/L.The ethyl acetate fraction from stems of P.orientale collected in fall had very strong contact toxicity against 4th instar larvae of P.rapae or 5th instar larvae of M.separate with corrected mortalities of 100% or 59.20%(33.60 g/L).Petroleum ether extract from stems of P.orientale in blossom had stronger contact toxicity against Aphis gossypii,with corrected mortality of 51.65%(0.27 g/L).Petroleum ether and methanol extracts from flowers of P.orientale in blossom had very strong contact toxicity against Tetranychus cinnabarinus,with corrected mortality of 100%(0.13 and 1.15 g/L).