Toxicity and Efficacy of Six Insecticides on Field Population of Nilaparvata lugens(Stal)

The stem-dipping of rice stalks was used to determine the susceptibility of Nilaparvata lugens(Stl)to 6 insecticides.Different field populations collected from 3 regions in Fujian from 2009 to 2010 were used for the study.The experiment was conducted by spraying the insecticides during the beginning of the peak N.lugens nymph-hatching in the late-rice growing field at Xianyou County.The results showed that the susceptibility of N.lugens nymphs to insecticides decreased with the insect's age.The toxicity of nitenpyram to N.lugens was the highest among the 6 insecticides.The LC50 on the 2nd,3rd and 4-5th instar nyphms of N.lugens populations were 0.9417-1.0167 mg·L-1,1.187 2-1.341 0 mg·L-1 and 1.6102-1.9370 mg·L-1,respectively.Isoprocarb exhibited the lowest toxicity among all insecticides tested,with LC50 on 2nd,3rd and 4-5th instar nyphms of 37.118 3-46.7335 mg·L-1,45.924 1-56.9504 mg·L-1 and 50.993 8-70.1912 mg·L-1,respectively.The insecticide resistance to imidacloprid of the N.lugens population in Fuzhou was considered high,and the population in Longhai and Xianyou extremely high;and,that of all 3 N.lugens populations moderate to thiamethoxam,buprofezin and isoprocarb.All 3 populations were susceptible to nitenpyram.Among the 6 insecticides,nitenpyram and isoprocarb exhibited a control effect on the field populations of N.lugens more rapidly than the others.But,the control effect of nitenpyram and pymetrozine lasted longer than that of the others.In the beginning of the peak N.lugens nymph-hatching,imidacloprid was effective with a dosage of 30-45 g(a.i.)hm-2.In recent years,the serious insecticide resistance and the declined efficacy of imidacloprid,long-term applications to control N.lugens with large dose have become inappropriate and inpractical.Alternative strategies,such as alternating and rotating the use of different insecticides,need to be explored.It was postulated that nitenpyram and/or pymetrozine could be the candidates as replacements for imidacloprid.