Insecticidal effects of extracts from Polygonum orientale L. and their action ways against Mythimna separate Walker.

Insecticidal activities of Polygonum orientale L.were seldom reported at home and abroad and the action ways of extracts from P.orientale against Mythimna separate Walker has not been investigated up till now.Study on insecticidal activities and action ways of the extracts can provide theoretical basis for formulating new type of botanical insecticides.The paper conducted insecticidal activities of extracts from P.orientale and their action ways against M.separate using immersion and sandwich methods.The results show that the extracts from seeds and stems in autumn had the highest effects and the contact mortality of methanol extract(diluted 5 times) against the 5th instar larvae of M.separate were 21.18% and 20.29%,respectively.Among the different solvent extracts,the ethanol extract from seeds had the strongest contact effect against the larvae,the adjusted mortality was 41.97%;the adjusted mortality of the methanol extract from stems in autumn was 20.29%.The adjusted mortalities of ethyl acetate extract from seeds and stems in autumn were 88.89% and 59.20%,respectively;the values of LC50 were 8.6466 and 29.0484 g·L-1(extracts).The contact mortalities of the two extracts(diluted 10 times) were all 100% against the 4th instar larvae of Pieris rapae L.The contact mortalities of ethyl acetate extract(diluted 5 times) from seeds were 70.27,87.5,and 90.00% against the 3rd instar larvae of Plutella xylostella L.,the fifth instar larvae of Helicoverpa armigera Hubner and Mamestra brassicae L.The ethyl acetate extract from seeds had stomach poisoning effect against the 3rd instar larvae and the adjusted mortality was 57.14%;the inhibition rate of ethyl acetate extract from stems in autumn against the 3rd instar larvae was 30.45%.