Impact of pesticides used in paddy fields on the population of Laodelphax striatellus Fallén

For the purpose of understanding the toxicity and long-term effects of pesticides used in paddy fields on Laodelphax striatellus Fallen in order to control the pest scientifically and effectively,the toxicities of 14 pesticides and joint actions of 10 pesticides mixtures to Nilaparvata lugens Stl and L.striatellus were tested in laboratory by rice-stem dipping method.Long-term effects of triazophos,lambda-cyhalothrin,chlorpyrifos and buprofezin-chlorpyrifos on L.striatellus were detected as well.The toxicities of pymetrozine,buprofezin,acetamiprid and metolcarb to N.lugens were significantly higher than those to L.striatellus.The mixtures of imidacloprid-isoprocarb,imidacloprid-fenobucarb,buprofezin-chlorpyrifos,buprofezin-carbary1,buprofezin-dimethacarb and buprofezin-metolcarb were synergistic to N.lugens and antagonistic to L.striatellus,and the toxicities of the 9 mixtures to N.lugens were significantly higher than those to L.striatellus except for the mixture of imidacloprid-chlorpyrifos.The toxicities of triazophos,lambda-cyhalothrin,chlorpyrifos to the nymph of L.striatellus were much greater than to the adult.Triazophos,chlorpyrifos and lambda-cyhalothrin used in late stage of rice growth improved reproduction of L.striatellus in varying degrees,there by increasing wintering quantity of L.striatellus and the number of the pest immigrating to rice seedling bed next year.In conclusion,the doses of pymetrozine,buprofezin,acetamiprid,metolcarb,imidaclopridphoxim,imidacloprid-metolcarb,imidacloprid-isoprocarb,imidacloprid-fenobucarb,buprofezin-imidacloprid,buprofezincarbary1,buprofezin-dimethacarb and buprofezin-metolcarb controlling N.lugens could not control the population of L.striatellus.Triazophos,chlorpyrifos,lambda-cyhalothrin and buprofezin-chlorpyrifos boosted the population of L.striatellus when used in rice field.Instead of controlling L.striatellus,triazophos,chlorpyrifos and lambda-cyhalothrin actually promoted the breeding of the pest.