Xu Hongxing

Ecological Fitness of Non-vector Planthopper Sogatella furcifera on Rice Plants Infected with Rice Black Streaked Dwarf Virus

We evaluated the effects of rice black streak dwarf virus (RBSDV)-infested rice plants on the ecological parameters and its relevant defensive and detoxification enzymes of white-backed planthopper (WBPH) in laboratory for exploring the relationship between RBSDV and the non-vector planthopper. The results showed that nymph survival rate, female adult weight and fecundity, and egg hatchability of WBPH fed on RBSDV-infested rice plants did not markedly differ from those on healthy plants, whereas the female adult longevity and egg duration significantly shortened on diseased plants. Furthermore, significantly higher activities of defensive enzymes (dismutase, catalase and peroxidase) and detoxification enzymes (acetylcholinesterase, carboxylesterase and glutathione S-transferase) were found in WBPH adults fed on infected plants. Results implied that infestation by RBSDV increased the ecological fitness of non-vector planthopper population.

High Temperature Modifies Resistance Performances of Rice Varieties to Brown Planthopper, Nilaparvata lugens (Stål)

To investigate the effect of temperature on the resistance characteristics of rice varieties with different resistance genes to brown planthopper (BPH), Nilaparvata lugens (Stal), the resistances of IR26 (Bph1) and IR36 (bph2) to BPH population in Hangzhou, China were monitored in greenhouse during September in 2007 and 2008 by using the standard seedling screening techniques (SSST) developed by the International Rice Research Institute (IRRI). Furthermore, the changes in resistance of IR26 and IR36 to BPH, soluble sugar and oxalic acid contents in 25-day-old rice plants of susceptible variety TN1 and resistant varieties IR26 and IR36 were detected at five temperatures (22oC, 25oC, 28oC, 31oC and 34oC). IR26 completely lost resistance both in greenhouse and at the five tested temperatures. IR36 still had moderate resistance at natural temperature, but its resistance decreased gradually when the temperature increased from 25oC to 34oC, and fully lost its resistance at 31oC and 34oC. The highest durable resistance of IR26 and IR36 were recorded at 25oC. The soluble sugar content in plants of the three tested rice varieties increased with temperature increase, and the oxalic acid content increased with the temperature increase at first, maximized at 25oC, and then declined. Two-way ANOVA indicated significant effects of temperature and rice variety on contents of soluble sugar and oxalic acid in rice plants.

Bacterial Community in Different Populations of Rice Brown Planthopper Nilaparvata lugens (Stål)

Abstract The structures of bacterial communities in the brown planthopper (BPH) Nilaparvata lugens (Stal) from different geographic and resistant virulent populations were analyzed by using denatured gradient gel electrophoresis (DGGE). Results showed that the bacterial communities in BPH nymph from the first to the fifth instars varied with nymphal growth and development. The bacterial communities in the first-instar BPH nymph were similar to those in adults. Nine geographic BPH populations were divided into three groups based on the cluster analysis of DGGE fingerprint. The first group was from the Philippines; the second group was from Thailand and Hainan, Yunnan and Zhejiang provinces of China; and the third group was from Vietnam and Guangxi, Hunan and Jiangxi provinces of China. BPH populations adapted to different resistant rice varieties. The BPH populations from Mudgo (with resistant gene Bph1) and ASD7 (with resistant gene bph2) differed with those of the susceptible rice variety TN1.

Changes in Endosymbiotic Bacteria of Brown Planthoppers During the Process of Adaptation to Different Resistant Rice Varieties

ABSTRACT The specific primers of five species of endosymbiotic bacteria were designed to determine their numbers in three virulent populations of brown planthopper, Nilapavata lugens Stål, and to assess changes during adaptation to different resistant varieties using fluorescent quantitative PCR. The results showed that Chryseobacterium was the dominant bacteria in all three populations of brown planthopper, followed by Acinetobacter in TN1 population, Arsenophonus and Serratia in Mudgo population, and Arthrobacter and Acinetobacter in ASD7 population. When the TN1 population of brown planthopper was transferred to ASD7 (with resistant gene bph2) rice plants, Chryseobacterium was still the dominant bacteria, but the originally subdominant Acinetobacter declined to a level that was not significantly different from that of other endosymbiotic bacteria. After they were transferred to Mudgo (with resistant gene Bph1), Serratia and Arsenophonus increased significantly and became the dominant bacteria. However, they declined to a level that was not significantly different from that of the three other species after two generations. When ASD7 and Mudgo populations of brown planthopper were transferred to the susceptible variety TN1, the community of endosymbiotic bacteria in the ASD7 population of brown planthopper showed no significant changes. However, the numbers of Acinetobacter and Arthrobacter in the Mudgo population of brown planthopper exhibited a transient increase and returned to their original levels after two generations. After the Mudgo population of brown planthopper was transferred to ASD7 rice plants, the quantity of endosymbiotic bacteria fluctuated, but the bacterial structure did not change significantly. However, after the ASD7 population of brown planthopper was transferred to the Mudgo rice plants, the bacterial structure changed significantly. Serratia and Arsenophonus increased significantly and became dominant. Although Serratia and Arsenophonus decreased significantly after a generation, they were still greater than Chryseobacterium. It was presumed that Chryseobacterium was dominant in all three populations of virulent brown planthoppers, but had no significant effect on virulence variation of brown planthopper. However, Serratia and Arsenophonus might be correlated with virulence variation of brown planthopper.

Susceptibility to Insecticides and Ecological Fitness in Resistant Rice Varieties of Field Nilaparvata lugens Stål Population Free from Insecticides in Laboratory

A population of rice brown planthopper (BPH) Nilaparvata lugens collected from a paddy field in Hangzhou was successively reared on susceptible rice Taichung Native 1 (TN1) in a laboratory free from insecticides for more than 14 generations. The changes in susceptibility to insecticides and ecological fitness on different resistant rice varieties were monitored in each generation. The resistance ratio to imidacloprid sharply declined with the succession of rearing generations without insecticides from 359.94-fold at F1 to 6.50-fold at F14 compared with the susceptible strain, and the resistance ratio to chlorpyrifos was from 9.90-fold at F1 to 5.94-fold at F14. Nymphal duration and weights of newly hatched female adults were significantly affected by rice variety, generation and their interactions, but nymphal survival was significantly affected by the generation only. The ratio of brachypterous adults in males was affected by the generation and generation × variety interaction, whereas no difference was found in females. Nymphal duration extended with increasing generations, and the female nymphal duration was shorter in the susceptible variety TN1 than those in the resistant varieties IR26 and IR36. In addition, the female adult weight in TN1 was higher than those in IR26 and IR36. These results indicated that the resistance of field BPH population to insecticides was reversed after several generations of no-exposure to insecticides, and the ecological fitness in TN1 was higher than those in IR26 and IR36. These findings suggested the rational and reduced use of insecticides in combination with the manipulation of resistant rice varieties would be effective for BPH management.