| Rice planthoppers, including the brown planthopper(BPH), Nilaparvata lugens(St?l), and the white-backed planthopper(WBPH), Sogatella furcifera(Horváth), are typical long-distance migratory rice pests in China and other countries in Asia. In recent years the frequency and serverity of the outbreak of rice planthoppers increased, and caused a great threat to rice production in China. Temperature increased the initial populations of rice planthopper in many countries in southeast Asia. However, the key factors that caused the outbreak of BPH and WBPH in China include earlier immigration time, more immigration events, high number of immigrants, and higher reproductive rate in the field. In this study, we firstly collected the first appearance data of immigrants of rice planthoppers based on light trap data in 2001-2013. Then, we used the geographic information system(GIS) to analyze the spatial distribution of the first appearance date of in recent 10 years. Furthermore, we identified the source areas of WBPH migrants in different locations, and calculated effective accumulative temperature in order to find the relationship between temperature and light trap data. Moreover, we simulated the condition of short-term exposure to high temperature clarify effects of the survival and fecundity of BPH to see how BPH response to the heat stress under global warming stress. Our results provided the information of the influence of temperature on the migration and reproduction of rice planthoppers, and will help us to predict and manage the outbreak of rice planthoppers in China. The results were as follows:1 Distribution of the first appearance date of rice planthoppers, WBHP and BPH, during 2001 to 2013.The objective of this study is to clarify the fluctuation of the first apperance date of rice planthoppers under light traps into south part of China. The light trap data of WBPH and BPH from 2001 to 2013 at major rice production areas were collected and analysised by using spatial analysis function in Arc GIS. Results suggested that the immigration of WBPH occurred earlier than BPH. The first appearance date of rice planthoppers was earlier at the east part of China than the west on the same latitude. Comparing to other years, WBPH and BPH immigrated earlier into China in 2006, 2007 and 2008. Results were used to compare with the published data from 1977 to 1995 in order to find how the global warming influence the first appearance date of rice planthoppers in China. The result showed the influence varies according to different locations. Comparing with the period from 1977 to 1995, the first appearance date was earlier at the south China rice production area, and was almost the same in the middle and lower reaches of Yangzi River rice production areas, but appeared a little bit late in south Yangzi River rice production areas.2 The influence of the average monthly temperature on the migration, an initial immigration periods of WBPH.In this part, we tried to use the back trajectory model(HYSPLIT) to find the source areas of WBPH that migrated into different locations, and used to find out if the average monthly temperature in source areas will affect the first appearance date in the immigrated areas. We found that average monthly temperature and the first appearance date were no significantly correlated, except two locations(Taicang, Anhui province and Longzhou, Guangxi province).The first appearance date in Longzhou, Guangxi had a significant negative correlation with the average temperature in February at region 31(North Vietnam and Hanoi)(R=-0.578*), indicated that the higher the average temperature in February in Hanoi, North Vietnam, the earlier the date of first appearance in Longzhou. The lowest monthly temperature in February in Hanoi, Vietnam was 14.6℃, which is almost 4 degree lower than the average monthly temperature during 2001 to 2013. Therefore, the first apperance date in Longzhou was 7 d later than the average appearance date in the period of 2001 to 2013. During the years that the higher average monthly temperature in February was high in 2007 and 2009, the date of first apperance in Longzhou was 12 d and 5 d earlier than normal. Longzhou, Guangxi locates at the border of Chian and Vietnam, with sub-tropical climate, and few WBPH can overwinter in this area.3 Effects of short-term exposure to high temperature on the survival and fecundity of BPH.The objective of this study is to clarify effects of brief high temperature exposure on survival and fecundity of BPH. The survival rate, reproduction and the survival rate from egg to adult of F1 progeny of BPH were evaluated after the adults exposed to 33, 35, 37, 39, 39.5 and 40℃ for 2 h, respectively and then kept in the incubator at 25℃ for breeding. Within the range of 33-37℃, the survival rate and fecundity of BPH were not significantly different from untreated adults. Within the range of 39-40℃, the survival rate of BPH were decreased. After exposure to 39.5℃for 2 h, the survival of male and female adults were less than 50%. After exposure to 40℃ for 2 h, the female adult survival rates dropped to 4.5%, and the male adults were 6.7%. All of the adults died within 24 h. Furthermore, high temperature had an adverse effect on fecundity of female adult. The average fecundity distinctly decreased under exposure of high temperature for 2 h. The total survival rate from egg to adult of F1 progeny was significantly reduced when the adults exposed to 33-39.5℃. With the temperature increasing, the total survival rate from egg to adult of F1 progeny decreased from 80.4% to 61.8-75.5%. Female adults ceased oviposition activities after exposure to 40℃. The oviposition rhythms and the number of eggs of F1 progeny hatching per day also changed in these heat shock treatments, with prolonged oviposition period and F1 progeny hatching peak period after exposured to 39.5℃. The survival and reproduction of BPH significantly decreased after exposured to temperatures of 39-40 ℃. When the exposure temperature exceed 39℃, it has the potential threats to the survival and fecundity of BPH. |
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