Abstract: Dynamics of the symbiote was monitored in different geographic and virulent populations of the brown planthopper (BPH), Nilaparvata lugens Stal, to determine its role in nymphal feeding selection, development and adult reproduction.Effect of symbiote on the activity of transaminases in BPH feeding on different resistant rice varieties was also examined. The results showed that the virulence of BPH to rice resistant varieties was closely related to number of the symbiote in BPH from the paddy fields, and abundance of the symbiote in BPH from Guangxi Province was markedly greater than that from Hangzhou and Longyou in Zhejiang Province, while no obvious differences in numerical dynamics of the symbiote were found among the three purified populations with different virulence to the resistant varieties (biotype Ⅰ, Ⅱ and Ⅲ) from the greenhouse in International Rice Research Institute (IRRI). Number of the symbiote reduced significantly in female adult of BPH biotype Ⅰ on resistant rice varieties IR26, Mudgo and ASD7 compared with that on susceptible rice variety TN1. The aposymbiotic nymph of biotype Ⅰ and Ⅱ treated by high temperature in egg stage preferred TN1 and ASD7 to Mudgo. The markedly lower nymphal survival rate, adult fecundity and activities of alanine transaminase and aspartic transminase, and longer nymphal duration were recorded in the three aposymbiotic biotypes than in control ones on susceptible and resistant rice varieties, however, the much greater changes occurred in the three tested biotypes when they fed on inadaptable resistant rice varieties. These results implied that the symbiote should play an important role in change of virulence of BPH population to resistant rice varieties.

Key words: Nilaparvata lugens, endosymbiote, virulence, resistant rice varieties