Effective duration of pesticide-induced susceptibility of rice to brown planthopper (Nilaparvata lugensStål, Homoptera: Delphacidae), and physiological and biochemical changes in rice plants following pesticide application

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Abstract
The effective durations of pesticide-induced susceptibility of rice to brown planthopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and physiological and biochemical changes in rice plants following pesticide applications, were studied. The effective duration of the herbicide butachlor on the susceptibility of rice variety Zhengdao 2 to BPH exceeded 16 days. The difference in damage rating between rice plants with pesticide treatments and control plants gradually decreased with days after treatment (DAT). There was a significant correlation between damage rating and DAT. The number of rice tillers at 3 – 10 DAT and plant heights at 7 – 10 DAT declined on Zhengdao 2 with the butachlor treatment. On the other hand, there were no effects of butachlor on damage rating, number of rice tillers and plant height for Xiushui 63. This might be related to tolerance of Xiushui 63 to butachlor. For Zhengdao 2, the fungicide jingganmycin and the insecticide bisultap had a significant influence on BPH damage, number of rice tillers and plant height. In contrast to butachlor, jingganmycin and bisultap had a significant effect on BPH damage to Xiushui 63. However, these two pesticides had no significant effect on the number of rice tillers and plant height of Xiushui 63. In general, the effective duration of butachlor on rice plants was greater than jingganmycin and bisultap. Oxalic acid content and photosynthesis in rice plants declined significantly after jingganmycin and bisultap treatments. These findings are consistent with those of pesticide-susceptibility of rice to BPH. Pesticide-induced susceptibility of rice resistance to BPH counteracts the role of varietal resistance in integrated pest management.