| The Pesticides Laboratory of the Institute of Plant Protection, Gansu Academy of Agricultural Sciences, screened out one kind of Polygonum plant from 84 plant samples which can kill insects effectively(according to the results of indoor biological investigation of contact effects to Mythimna separate Walker). At present, there is a little of research on bioactivity, spectrum of killing insects and its action way at home and abroad. Therefore, the studies on bioactivity, spectrum of kill insects and its action way of this kind of the plant would certainly fill the research blank, and the results will provide theory basis to develop and exploit new safe, effective plant source pesticide, also, have very important practical significance to innovation of science and technology production.The findings indicated that the rank order of output rates of different parts of the plant extracted by methyl alcohol were stem in autumn stage > leaf and flower initial bloom stage > stem in initial bloom stage > seed; the rank order of output rates extracted by 5 different polar solvents was methyl alcohol > ethyl alcohol > acetone> ethyl acetate > petroleum ether. There were few differences to the output rates of the seed extracted by absolute ethyl alcohol, 95% ethyl alcohol, 90% ethyl alcohol, 85% ethyl alcohol, 75% ethyl alcohol and 50% ethyl alcohol, and the output rates were 7.2%~8.9% which approach to that extracted by industrial ethyl alcohol; the output rates of the seed extracted by 95% methyl alcohol, 90% methyl alcohol and 85% methyl alcohol were higher than that extracted by 95% ethyl alcohol, 90% ethyl alcohol, 85% ethyl alcohol, and industrial methyl alcohol extracted by absolute methyl alcohol, 95% methyl alcohol, 90% methyl alcohol, 85% methyl alcohol, 75% methyl alcohol and 50% methyl alcohol. The output rates were 5.3%~18.94% of the stem in autumn stage extracted by 6 different water content ethyl alcohol and methyl alcohol ,the difference was obvious. From whole level, the output rate of stem in autumn stage extracted by methyl alcohol was higher than that extracted by ethyl alcohol.The results of indoor biological investigation showed that the contact effects to Mythimna separate Walker of the methanol extracts from the seed was the strongest, its death rate was 21.2%, and the stem in autumn stage was stronger and its death rate was 20.3%. The contact effects of the ethyl alcohol extracts from seed was the strongest, its death rate was 42%, the next was the methyl alcohol extracts, its death rate was 21.2%; but the contact effects of the methyl alcohol extracts from stem in autumn stage was the strongest, its death rate was 20.3%, the next was the ethyl alcohol, its death rate was 14.3%. So, the best extracting solvent of the seed was industrial ethyl alcohol and the best extracting solvent of stem in autumn stage was industrial methyl alcohol.There were almost not contact effects of the methanol extracts from the seed on Plutella xylostella L., Aphis gossypii Glover, Macrosiphum avenae Fabricius, Brevicoryne brassicae L., Aphis medacaginis Koch and Tetranychus cinnabarinus Boiduval; but the contact effects to Heliothis armigera Hubner, Mamestra brassicae L., Laphygma exigua Hubner and P. rapae L. were strongest, and the death rates were 54.76%, 63.33%, 46.67% and 21.30%, repectively. There were no antifeeding effects to Mythimna separate Walker and Pieris rapae L.; no stomach poisoning effects to Pieris rapae L.; no the systemic effects to Myzus persicae (Sulzer); no suffocating effects to Pieris rapae L. and Mythimna separate Walker; no narcotism and killing egg effect to Mythimna separate Walker.The methanol extracts from the seed have good low temperature stability. The death rate, which the contact effect to Mythimna separate Walker, of fresh methanol extracts dilution five times was 21.1%, the death rate, which the contact effect to Mythimna separate Walker, of methanol extracts dilution five times was 19.7%, and lower 1.4% than fresh methanol extracts.The death rate of contact effects from seed float and precipitate were 56.2% and 66.2% respectively, which were 2.66 times and 3.14 times to extracts respectively, but the middle-level solution was no killing action. The toxicity regression equation of float and precipitate was 1.6629+2.8035X±0.105 and 1.6269+3.0380X±0.075, respectively; the values of LC50 were 0.1550 and 0.1289g/ml, which showed contact effects of the float and precipitate were higher than methyl alcohol extracts, the toxicity of the precipitate was a little higher than that of the float. |
