Abstract: Field experiments in three sites in Zhejiang province were carried out for evaluation of efficacy and economic efficiency of formulation and dosage of pymetrozine in controlling rice planthoppers， by economic threshold model-based simple judgment rule of chemical control. Wettable granule （WG） of pymetrozine was as effective as suspension emulsion （SE） with the same rate of 75 g a.i.·hm-2 in controlling the small brown planthopper （SBPH）, Laodelphax striatellus, in rice panicle. Rates of 75 g a.i.·hm-2 and 1125 g a.i.·hm-2 of 50% pymetrozine WG had efficacies of 60%-97% from 1 to 21 days after treatment （DAT） for controlling SBPH and the white-backed planthopper, Sogatella furcifera, in mid-season of rice growth. Same rates of 50% pymetrozine WG obtained the efficacies of 77%-98% for the brown planthopper, Nilaparvata lugens, from 4 to 21 DAT. The trends of control efficacies for the three planthoppers species in the two experimental sites were similar and could be well\|fitted by Logistic models against DAT and reached the final maximum value of 98%， suggesting both the rates of the WG formulation of pymetrozine have fast and sustainable controlling effect for at least 21 days. The economic threshold model\|based simple judgment rule of chemical control indicated that 50% pymetrozine WG in a rate of 75 g a.i.·hm-2 is the optimal selection in control of the three species of rice planthoppers in both japonica rice and indica hybrid rice.

Key words: pymetrozine, rice planthopper, economic threshold model, chemical control