Study On Dynamic Regularity Of Laodelphaxstriatellus (Fall(?)n) Population In The Yangtze River Delta Region

The small brown planthopper Laodelphax striatellus (Fallen)(SBPH)(Hemiptera:Delphacidae), is one of the important pests harming agricultural production in China. SBPH can not only cause sap-sucking, spawning harm, they can also spread variety of plant diseases causing severe crop failures and even no harvest. Since the 21st century, the SBPH outbreak occurred frequently in our country, especially in the Yangtze River delta and the surrounding areas. In 2004 and 2005, SBPH outbreak in Jiangsu, Anhui provinces, which causes serious reduction of crop yield and wipes out crops in part of the fields. At the same time, the rice black-streaked dwarf disease and rice stripe disease were spread by SBPH in Southern and Northern Zhejiang, which covered the area of 53,300 hm2 and 23300 hm2. The reason why SBPH cause such catastrophe in this region prompting us to explore the occurrence regularity and mechanism.This paper explained this change by investigating and analyzing the population regularity of SBPH in Yangtze river delta during overwintering and summer period by analyzing the influence of low temperature and high temperature for biological characteristics of SBPH. We studied the source area of SBPH outbreaking in the late spring and early summer about the phototactic rhythm and the source area of SBPH which outbreak in the period of 2000-2010 in this region. Meanwhile, we confirm the distribution of SBPH in the Yangtze river delta and its surrounding area, by analysis the source area of this insect; and we illustrate the effects of the regional warming on SBPH occurrence by 30 years' light trapping data in Jiaxing, Zhejiang as an example. Our results are listed as follows:1 The analysis of character of overwintering SBPHWe had surveyed Jiangyan Jiangsu region for three years and found that: (1) In the second half of October, the last generation of adult insect of SBPH emerged in the field,which wing types were mainly long wings. Since the second half of October, SBPH growth rate start to slow down or even stop in the field, which was in preparation for overwintering.From the second half of November to March in the second year, the SBPH was in diapause state,which composed by 3rd-5th instar of the nymph of SBPH. Among of them,3rd instar was minor,4th and 5th instar were major. From the second half of March,there were adult SBPH emerged in the field, we think diapause state was over at this time. (2) During the overwintering period, the number of SBPH that could seen in the field was positive correlated to the temperature in daytime. (3) Crop residue was a good place for overwintering of SBPH. (4) The temperature in the winter of Jiangsu was hardly influences the survival rate of SBPH. (5) 4th and 5th instar of SBPH nymph were began to development after the temination of diapause and the eclosion peak were in the period of late March to early April, which wass relatively consistent. (6) The first generation of adult SBPH emerged in early Spring (by overwintering generation ), which was mainly composed by short wing of SBPH.The research of cold resistance of SBPH in the Yangtze river delta, Jiangyan Jiangsu area were showing that: (1) In the photoperiod L: D =10:14, the super-cooling point of 4th instar was lower than 3rd, 5th instar and adult insects.(2) ) The super-cooling point of 4th instar were different under the different photoperiods (L: D = 16:8 and L: D =10:14). (3)Under the short photoperiod (L: D = 10:14), the 4th instar of SBPH with different days after ecdysis had the different super-cooling point and 10 days after ecdysis is the lowest, then gradually increase. (4) Under the short photoperiod (L: D = 10:14), male adult with long wings have the lowest supercooling points, but female adult with short wings have the highest cooling point. There is no significant difference.2 The studies and applications phototactic rhythmof SBPH in late Spring and early Summer.We analyzed SBPH's phototactic rhythm by hourly light trap and hourly dissection in Nanjing Jiangsu, Fengtai Anhui from 2009 to 2010, at the same time, we studied the effect of rainfall on phototactic rhythm. Furthermore, we discussed the phototactic rhythm associated with ovary development progress in the peak period of SBPH in the application of rice planthopper forecast. The results showed that: (1) There was obvious phototactic rhythm of SBPH. At night, when there is no rain, the light trapping rhythm is "unimodal"model, the peak hour is between 19:00 to 21:00. If there is rain, rain will affect the quantity and time of the peak period in the night and the phototactic rhythm is the"multiple peak" model. (2) In the peak period of 19:00 to 21:00, the ovarian development level of the light-trapped female SBPH is affected by rainfall. When there is no rain, the ovarian development level is mainly from II to V level,and the property of insect's population is immigration type; When there is rainfall, ovarian development is on level I,and the population priority is emigrantion type.3 Analysis of the source areas of SBPH in Yangtze River delta of in the late Spring and early Summer(1) Using HYSPLIT trajectory analysis platform, we simulated source areas of the insects trapped under light on the peak days in many standings from 2000 to 2010 in Yangtze River delta, the results showed: (1) The insect source areas' distributions have certain differences in many sites of Jiangsu province. Gan Yu population's main source areas distribute in Anhui, Jiangsu and Jiangxi Province. Gaochun population's main source areas are in Jiangsu Province. Hongze population's main source areas distribute mainly in Anhui, Jiangsu and east of Henan Province. Pei County population's source areas mainly distribute in Jiangsu and Zhejiang Province. Zhangjiagang population's source area mainly distribute in Shandong, Anhui, Jiangsu, Henan and other places, parts are in the territory of Hebei.(2 ) In every site of Anhui province, Wuhu population's source areas mainly distribute in the Anhui, Jiangsu, Jiangxi and Eastern Guizhou. FeiDong population's source areas mainly distribute in Henan and AnhuiProvinces. Fengyang population's source areas are located in Anhui, Hubei, Shandong. GuangDe population's source areas are mainly located in the Southern Jiangsu and Jiangxi Province. Tongcheng population's source areas are mainly located in Anhui, Jiangxi and Guizhou.(3) The insect source areas in Zhejiang Province distributes intensively. Except Xiaoshan, the rest of the sites' (including the Xiangshan, Wenzhou, Shaoxing, Longyou)insect source area are mainly in Zhejiang, Fujian and Jiangxi. Xiaoshan's insect source areas mainly distribute in Jiangsu, Southern Anhui, Zhejiang and Jiangxi.(4) In Jinshan,Chongming,Fengxian,three sites of Shanghai,Jinshan's insect source areas distribute in the south of Anhui, Zhejiang and Jiangxi Province. Chongming's insect source areas distribute in Shanghai, Shandong, Anhui and Jiangsu Province. Fengxian's insect source areas distribute in Shanghai, and Jiangxi, Zhejiang Province.4 Population crashes of SBPH in Summer and high temperature's influence on its developmentSBPH population survey in Jiangyan region of Jiangsu, Haining region of Zhejiang,and Yongkang region of Zhejiang showed that the number of SBPH in the field presents low period in around August. Indoor experiments showed that: (1) Under 27 ?, the short light period (L: D = 4:20, L: D = 8:16, L: D = 10:14, L: D = 12:12), compared to long light period(L: D = 14:10 and 16:8), significantly prolong the 3, 4, 5 nymphs' development time.However under 30 ?, SBPH unobviously responses to the length of light, and high temperature can make SBPH have abnormal body color and dehydration. (2) High temperature greatly affect survival rate of SBPH. Under 30 ?C, the 4th and 5th instar of SBPH nymphs' death rate is more than 80%. (3) High temperature increases the number of individual feather deformity. (4) Compared to 27 ?, female SBPH's life and spawning quantity were significantly reduced under 30 ?. All in all, by the investigation of the field population dynamics and indoor simulation test, we conclude that the low period of SBPH field population in summer was not induced by diapauses under high temperature, but was induced by long development time, increased mortality, high rate of disabled adults and the low egg production induced by high temperature.5 Regional warming affect outbreak of SBPH in Jiaxing, Zhejiang30 years light trap data and relevant meteorological data analysis in Jiaxing, Zhejiang showed that: (1) The regional warming in Jiaxing causes SBPH main source areas distribution range to change, and it shows the trend of "the South shrinks and the North expands"; (2) The regional warming causes the time of SBPH outbreak to be in advance; (3)The Spring temperature rise is a key factor that causes SBPH to occur in advance.