In many cases over the years, we failed to forecast accurately outbreak of Rice stripe virus (RSV) disease using population density of overwintering small brown planthopper (SBPH), Laodelphax striatellus. What is the source of error in this viral disease assessment? For answering the question, spatial distribution of RSV in paddy fields was investigated in relation to the yield of rice grain, and the population density of overwintering SBPH in ridge of paddy fields. Total 14 paddy fields in 5 regions were surveyed in June, 2008. Disease assessment was carried out with each of 30 rice plants in the one of the borders, 5th, 10th line from ridge, and 90 rice plants in diagonal line for conventional method. The ears of rices from 18 plants in the same surveyed line were collected in the late of August for the weights of 100 rice grains. The infection rate of RSV was decreased by the distance from ridge; on the contrary, the increase tendency was shown in the yield of rice grains in the middle of paddy field. It is suggested that the border effect of viral distribution between ridge and paddy field is caused by the spatial distribution of the vector insect. Thus, in this case, the narrow border effect could represent that the SBPH migrated short distance from the ridge to paddy field. The conventional method, observing the disease in middle area of diagonal line, showed no correlation to the population density of overwintering vector generation in ridge. It might cause underestimation of the regional disease rate. The counting of RSV-diseased plant in border line only overestimated it also. However, the RSV infection rate in the near border had highly positive linear relationship (R2=0.91) to the regional average values by regression analysis. Therefore, the near border sampling method can improve the RSV disease risk assessment.

For the physiological study on environmental impact of genetically modified (GM) pepper plant on non-target but three-trophically related insect species, we investigated behavioral responses of Aphis gossypii and Aphidius colemani in Y-tube olfactometer to the cucumber mosaic virus (CMV)-resistant transgenic pepper plant (H15 GM line) expressing coat protein gene of CMV and its wild type pepper plant (untransformed, susceptible to CMV pathotype II, P2377 inbred line) in relation to CMV infection. CMV-infected plants were prepared with the 30 min of inoculation by the winged A. gossypii viruliferous or mechanical inoculation using CMV-Fny, and with molecular diagnosis using reverse transcriptase-polymerase chain reaction (RT-PCR) over 2 weeks after inoculation. In this study, time for attraction responses (attraction time) of A. gossypii were not significantly different in the pepper strain, and the virus infection of plant. However, the attraction time of A. colemani was significantly different between the GM plant and the non-GM plant. In addition, the attraction time of A. colemani to the GM plant was significantly decreased according to the CMV infection. For further study, the volatile organic compounds (VOCs) emitted by these plants were collected with an entrainment kit and analyzed by Gas Chromatography (GC) on HP-1 column. The specific VOCs related to CMV infection were detected in the GM plant over 4 weeks after inoculation of CMV in this study. Thus, it is suggested that VOCs of the GM plant in this study may be produced more as a signal attracting A. colemani in relation to CMV infection.