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Nilaparvata lugens (Stal) is a typical vascular feeder, primarily sucking the phloem sap of host plants. Its feeding on rice,Oryzasativa L., plants changes the pattern of allocation of assimilates between roots and shoots, and the root:shoot (R/S) ratio of assimilates is often measured as an index of physiological responses to N. lugens. The current study investigated changes in the R/S ratio of biomass, sucrose, and soluble sugar contents of rice plants in a susceptible variety (TN1) and a resistant variety (Xieyou 963). The results demonstrated that root and shoot biomasses in the two varieties linearly decreased with the increase of N. lugens infestation density. However, the relationship between changes in the R/S ratio of biomass andN.lugens density differed between rice varieties, with the R/S increasing with infestation density in TN1 and decreasing in Xieyou 963. Sucrose and soluble sugar contents and their R/S values were also signiÞcantly different between the two varieties. Compared with the control that was not infested by N. lugens, the R/S values of sucrose and soluble sugar at 3 days after infestation (DAI) increased but decreased at 6 DAI in TN1. The R/S values of sucrose and soluble sugar were higher at 6 DAI than those at 3 DAI in TN1, whereas these values were lower at 6 DAI than at 3 DAI in Xieyou 963. These contrasting results suggest that physiological responses to N. lugens infestation differ between the susceptible and tolerant rice varieties.

The use of selective insecticides in rice, Oryza sativa L., fields often causes resurgence of nontarget pest insects. This study was conducted to investigate the effect of two selective insecticides, buprofezin and imidacloprid, on Tryporyza incertulas (Walker), a nontarget pest. After larval feeding on rice plants treated with each insecticide, fecundity, ovary protein content, and titer of juvenile hormone III (JHIII) in the resulting female moths were determined with 'Xiushui 63' rice susceptible to T. incertulas and 'Zhendao 2' moderately resistant to T. incertulas. The fecundity of females developed from larvae that fed on the insecticide-treated Xiushui 63 plants was stimulated compared with that of moths from larvae that fed on rice plants that were not treated with either insecticide. There was no stimulating effect in females from larvae that fed on insecticide-treated Zhendao 2 plants. The weight of fourth instars (final instars) that fed on the insecticide-treated Xiushui 63 rice plants was significantly greater than that of control, increasing by 50.3 and 46.7% for 60 and 112.5 g (AI) ha(-1) buprofezin, and by 23.7 and 19.5% for 15 and 37.5 g (AI) ha(-1) imidacloprid treatments, respectively. Ovary protein content in adult females developed from larvae that fed on the rice treated with the high dose of buprofezin was significantly higher than that in control. For the high and low doses of imidacloprid during the second instar, and the low dose of imidacloprid during the fourth instar, JHIII titers in female adults were also significantly higher than that in control, increasing by 152.81, 90.52, and 114.19%, respectively.

The distribution of imidacloprid residue in different parts of rice, Oryza sativa L. (Graminales: Poaceae), plants was investigated for three rice varieties. Changes in larval hormones in Chilo suppressalis (Walker) (Lepidoptera: Pyralidae) that fed on imidacloprid-treated plant sources and the fecundity of resultant adult females (moths) also were determined. No significant differences in imidacloprid residue were detected in rice stem, leaves, and the unexpanded new leaf 7 d after treatment except in the rice variety Fengyouxiangzhan, in which residue content in leaves and the unexpanded new leaf was significantly lower than that in the stem. The percentage of reduction of imidacloprid residue after treatment varied with rice variety and plant parts. The greatest reduction in the three plant parts was shown in Wujing 15 compared with the other two varieties. The decomposition rate of imidacloprid residue in Wujing 15 was greater in leaves and unexpanded new leaf than in the stem, whereas in Wuyunjing 7 it was lower in leaves than in the unexpanded new leaf and stem. In Fengyouxiangzhan, the decomposition rate of imidacloprid in the stem increased 14 d after treatment. Juvenile hormone III and molting hormone titers in fourth instar larvae that had fed on rice plants treated with imidacloprid since the neonate stage were significantly higher than those in larvae fed on untreated plants (control). Juvenile hormone titer in larvae that had fed on Zizamia lalifolia Turcz galls treated with imidacloprid and the fecundity of the female moths that developed from such larvae were also significantly higher than that on the control counterparts. These results are discussed in relation to the impact of imidacloprid on nontarget insects and pest management.