A Study On The Influence Of Typhoons On The Migration Of Brown Planthopper Nilaparvata Lugens (Stal)

Brown planthopper (BPH Nilaparvata lugens (Stal)) is one of most harmful pests to rice in the temperate and tropical regions of East and South Asia. Over the past few years, BPH has become a particularly serious problem in the rice-growing regions of China, resulting in a broad and significant reduction in rice yield. Many environmental factors contribute to BPH migration. These factors primarily include agricultural settings, atmospheric background, and geographic conditions. Amongst these, typhoons are one of most important weather processes that affect BPH movement. Consequently, the structure and climate of typhoons like stream fields and precipitation will definitely influence the migration of brown planthopper. Case studies that analyze insect migration and its close relationship with typhoon development processes are rare. In China, however, the influence of typhoons on the migration of rice brown planthopper (BPH) has recently been widely reported, especially in2005and2006. In order to comprehensively determine typhoon’s mechanism of influence on BPH migration, we examined the motion, vortex airflow, precipitation, wind direction, and the speed of horizontal and vertical sections through the storm’s movement passage, and correlated these with the effects of the typhoon on light trap catches and variations in insect migratory trajectory, as well as immigrant source regions. The main results are as follows:1. There are mainly three types of typhoons land and affect BPH migration in China:(1) The westward-moving type(type I), whose tracks appear mostly at15°-25°N, moves westward and occurs during May to early July and early September to November. They mainly affect the South China rice area including paddy field in Guangdong, Guangxi, Hunan and even in Guizhou and Sichuan. For example, the Lionrock and Chanthu happened in2010.(2)The westering extended typhoon (type Ⅱ) is characterised by tracks that appear mostly at25°-30°N and extend westward to land. They often occur from July to August. The type II typhoons mainly affect the paddy field in the middle of China including Fujian, Jiangxi, Hunan etc., which can take Sanvu and Haitang occured in2005as examples.(3)The west-turning-northeast type(type Ⅲ) occurs from July to early September, and has tracks that appear primarily at25°-35°N, go ashore, turn northeast, and pass through the east coast areas. They often influence the rice regions in Zhejiang, Jiangsu, Shanghai, and Anhui etc. For instance, Khanun occured in2005and Wipha happened in2007.2. The influence of typhoon Meranti(typeⅢ) on brown planthopper migration were analyzed through the typhoon track and stream fields in September,2010. The analysis of the complicated typhonic property of Meranti which occurred combined with the east side coast geographical position of Zhejiang, the inference of topic cyclone Meranti for migration of rice brown planthopper was of mesoscale. The areas of incidence between the source regions to different immigration spots were far smaller than that of the common horizontal flow field or low-level jet stream. Besides, during the transit intraday of typhoon, the amounts of light trap catches BPH exhibited significant heterogeneity among the observation spots. It seems that the highest catches was not coincided with the nearest range from center of typhoon eye, in which were small in wind speed and rainfall as well as the downdraft and all are not in favor for BPH concentrated descending, but coincided with the spiral rain and gale belt within or near the side of eye wall, in which was in favor for BPH concentrated descending. In addition, the source regions of immigrant were most nearby places in the south of Zhejiang and northwestward of Fujian.3. The typhoon Talim(type II) which happened in August,2005had a huge influence on brown planthopper migration in terms of coverage and BPH migration distance. Compared with the distance of BPH migration influenced by typhoon center, the range of peripheral influence was far bigger, which even larger than that of common horizontal flow field and can reached800km. Besides, the light trap catches occurred in Xinluo during the transit intraday of typhoon certify the conclusion that the highest catches was not coincided with the nearest range from center of typhoon eye but coincided with the inner side of eye wall,100km away from typhoon center. In addition, the source regions of immigrant were places in the middle and northeast part of Jiangxi, west and north of Fujian and south of Zhejiang.4. Compared with the other two types of typhoon, the typhoon Fanapi(type I) which occurred in September,2010exerted a big influence on brown planthopper migration in terms of time and range of influence. The light trapping peaks in Guangdong during the transit intraday verify the conclusion again that the inner side of eye wall was the most probably places for BPH landing instead of typhoon eye zone. However, as the amounts of BPH in the source areas were small, the influence of typhoon Fanapi was small in the way of immigration BPH number. It also demonstrated that the influence of typhoon on BPH migration was not only determined by the strength and lasting time of typhoons themselves, but also affected by the amounts of BPH in the source regions. In addition, the source areas of immigrant were regions in the middle of Zhejiang, middle and south part of Jiangxi, west and south of Fujian, south of Hunan and east and north of Guangdong.5. In summary, combined with the three cases of typhoons analyzed, the conclusion can be drew that the range of influence by typhoon periphery is the biggest before the advent of typhoon, larger than the range after the pass of typhoon. And the range of influence by typhoon center is the smallest during the transit intraday of typhoon.