| Rice is an important food crop in the world,also is the main food crop in China.More than 4 million hectares rice is cultivated in Hunan Province,and contributes as much as 23 million tons of rice,which the area sown and total yield rank the second and first position in the nationwide,respectively.The planthopper,which mainly are brown planthopper(BPH),Nilaparvata lugens(St(?)l),and whitebacked planthopper(WBPH),Sogatella furcifera(Horváth),in Hunan Province,is one of the most destructive pests of rice in East,South and Southeast Asia.The planthopper does not only cause significant yield loss,even makes rice crops unharvestable by"hopperburn".Moreover,they act as vectors of some viral diseases of rice,such as rice ragged stunt virus and southern rice black-streak dwarf virus.It is well known that planthopper is a long-distance migratory insect.Hunan Province is located at a critical juncture of the migration route in spring-summer and the return migrant route in autumn.However,many scientific problems on migratory habits and comprehensive analysis of population dynamics of BPH and WBPH in Hunan Province are still poorly.Therefore,it is necessary for us to analyze the population dynamics and migratory habits of planthopper in Hunan Province.Also,the study on source areas of WBPH and BPH in Hunan Province will be beneficial for the prediction and suppression of these pests in southern China and other parts of the country.In this paper,the data about 25 planthopper monitoring stations for recent 7 years for BPH and WBPH population dynamics and light-trap catches were collected,and the light-trap catches and population migratory characteristics of BPH and WBPH from light-trap and field were analyzed,especially in Linxiang,Ningxiang,Hanshou,Danxian,Longshan,Dongan and Yizhang planthopper monitoring stations.Moreover,a last three-year study on ovarian development of BPH and WBPH from light-trap and field was carried out to clarify the population migratory characteristics.Meanwhile,the other last three-year study on take-off of BPH and WBPH in Hunan Province by cage experiment was conducted to obtain the data of biological characteristics of planthopper on take-off,such as take-off amount,take-off duration and take-off peak time.Based on the above research,combined with the national major rice-producing region 141 planthopper monitoring stations light-trap catches and field population dynamics of planthopper,the immigration areas of WBPH in early rice and BPH in late rice in Hunan Province were analyzed by trajectory analysis with HYSPLIT(Hybrid Single-particle Lagrangian Integrated Trajectory),which was a a trajectory analysis software for the simulation of migration pathways.Meanwhile,the landing mechanism of BPH and WBPH were analyzed by using GrADS and ArcGIS to understand the weather backgrounds during the major immigration periods.1 Occurrence regularity of N.lugens and S.furcifera in Hunan Province(1)The WBPH first appearance mainly occurred from late April to early May in North of Hunan Province,and the BPH was intensively occur from late April to mid-May.But,in South of Hunan Province,the WBPH first appearance mainly occurred more early than that in North,even as early as in late March,however,the first appearance BPH was mainly recorded from late April to early May.The major immigration period of planthopper in early rice in Hunan Province mostly observed in early June,late June and early July,and in late rice mainly recorded in early August,early September and late September.(2)The dynamics of planthopper in field in Hunan Province was described as follow:BPH migrated sporadically into Hunan Province between late April and early May and WBPH mainly recorded in mid-late March.Large waves of migratory BPH and WBPH continued to migrate into Hunan Province during late May and early June,late June and early July,which contributed the first nymph peak of the second planthopper generation(mainly by WBPH)in the field,with most serious destruction.In mid-July,BPH and WBPH adult appeared constantly,which lead to the adult peak of the third planthopper generation.In mid-late July,large scale early rice was harvested and planthopper lost the appropriate habitat,but with the bridge-rice expanded,the second nymph peak of planthopper occurred in mid-rice.In early August,planthopper,especially BPH,immigrate unceasingly to Hunan Province,which resulted in the nymph peak of the fourth planthopper generation.Subsequently,the BPH adult peak occurred in mid-late August.Additionally,huge amount of BPH immigrate into Hunan Province successfully,the most destructive generation of planthopper pose a threat to rice by the BPH nymph in September.In early October,the resident planthopper that mostly could not emigrate successfully lay the sixth generation eggs,but the generation circle could not develop successfully for the low temperature.(3)In May,June,August and September,both highest percentage of ovarian development grades of BPH and WBPH,which were collected in light-trap,was recorded as Grade II,with a value of up to 80-90%,and the second was Grade I,but other lever ovaries were quite low.However,in July and October,the percentage of Grade II ovarian development of BPH and WBPH presented obviously reduced tendency,and the Grade I ovarian development had increased obviously.Moreover,the results showed there were differences in ovarian development grades between BPH and WBPH.(4)However,according to the ovarian development grades of BPH in the field,with the characteristics that the proportion of high lever ovarian development(Grade III and even higher grade)was higher than the low lever(Grade Ⅰ and Grade Ⅱ),it was reasonability to consider the BPH that immigrated into Hunan Province before late-June as immigration population.But the BPH collected between late June and harvest were considered as local breeding population by the evidence,which each ovarian development grades had the approximately proportion.In late rice,BPH were estimated to be immigrants,because of the high proportion of high lever ovarian development before mid-August.Between late August and early September,due to the annual variation in amount of BPH immigrants,the BPH in the field were estimated either immigration population or local breeding population.In late September,the BPH were considered typically as emigration population for the rapid increase of low lever ovarian development grades.(5)With the same method,the WBPH collected in the field before June were considered as immigration population,and the early and mid-June were considered as local breeding population and migratory population.But,between late June and harvest,the WBPH were estimated to be mostly emigrants and portly local resident population.In late rice,the WBPH were regarded as migratory and local resident population,but,from then on,affected by the weather condition during the emigrant period,the WBPH were regarded as emigration population or mostly emigrants and portly local resident population.2 Take-off behaviors of N.lugens and S.furceifera(1)The cage experiment showed the results that temperature at take-off peak of BPH and WBPH ranged from 17.2℃ to 33.8℃,and there was a decrease tendency for temperature at take-off peak along with date to be observed.The results also expound that the light intensity at take-off peak of BPH and WBPH was less 100 lux.But the light intensity increased drastically from late September,with the value up to 462.4 lux.These results inferred that the key factor that triggered the take-off behaviors of BPH and WBPH before late-September was light intensity,but from then on,the key factor was temperature.The raining was a significant disadvantageous factor for take-off behaviors of BPH and WBPH.The time of climbing up to flag leaf for BPH and WBPH was both in advance with passing time,and period of preflight gradually increased.The duration of take-off for WBPH was longer than BPH before mid-September,whereas the BPH become more longer in later stage.(2)The ovarian development grades of female BPH and WBPH that were collected in the cage net showed that the highest proportion were recorded in GradeⅠ,the second one is Grade Ⅱ,but there was an unusual phenomenon that the third one is Grade V,the Grade Ⅲ and Grade IV were rarely founded in BPH.3 Migratory habits of S.furcifera in early rice in Hunan Province(1)With the trajectory analysis by HYSPLIT model,the mostly possible source area of WBPH immigrated in early and mid May was mid-northern Vietnam,northeastern and mid-regional Laos,even southern part of 22°N in China,such as Hainan Province,and the coastal area of southern Guangxi and Guangdong province.In late May,the source area of WBPH expounded to southern part of 25°N of most rice cultivated region of Guangxi and Guangdong province.In early June,the WBPH immigrated into Hunan Province from Hainan,Guangxi and Guangdong province.And as time passed,in mid-late June,the source areas of WBPH were located in mid-northern Vietnam,mid-regional Laos and Thailand,and the southern part of 27°N in Hunan,Jiangxi,Guangdong,Guangxi and Hainan Province also were the possible source area.In early July,the source area furthered to extend to southern part of 30°N of rice cultivated regions in Hunan and Jiangxi Province.(2)In early rice,the carrying force for WBPH immigrating into Hunan Province was southwest airflow that was the leading airstream,south airflow and southeast airflow,which derived from the Bay of Bengal,South China Sea and western Pacific,and the proportions were 64.51%,23.59%and 11.90%,respectively.Southwest airflow could carry WBPH from northern Indochina Peninsula entering Hunan Province,especially,strong southwest lower-level jet provided large-scale atmospheric circulation for WBPH entering Hunan Province from central and southeastern Indochina Peninsula.The south airflow and southeast airflow could give assistance for WBPH immigration from Hainan,Guangdong and Jiangxi Province.(3)Based on the analysis on the meteorological background,the results showed that rainfall and wind shear were the main reasons for WBPH landing in early rice of Hunan Province,which the ratio were 60.74%and 21.72%,respectively.And a large range durative heavy rainfall could carry waves WBPH entering Hunan Province.Moreover,WBPH was not completely passive in choosing zone of rainfall as the landing area,it was reasonable to believe that the edge of the south area of rainfall was more benefit for WBPH landing,which resulted in more catch peaks were founded along the south area of rainfall in early rice of Hunan Province.Apart from rainfall and wind shear,the ceiling of the threshold temperature of flying WBPH in atmosphere was another main impact factors for the concentrated landing of WBPH in early rice of Hunan Province,especially in May,with the vulue of 1.58%to total peaks.4 Migratory habits of N.lugens in late rice in Hunan Province(1)In the first half of August,the source areas of BPH immigrated into Hunan Province were located in hilly regions of southwest part in Hunan Province,where the early rice was harvested in the early August,and originated the border of northern Guangxi Province.What deserves to be noticed is that,since the fourth pentad in August,the source areas of BPH were changed from South China rice cultivated regions to Yangtze and Huaihe river area,such as single rice regions in western and northern Anhui Province and northern Jiangsu Province.In late August,the BPH were mostly came from the junction of Anhui,Jiangsu and Zhejiang Province,as well as northern part of 31 °N in Hubei Province rice regions.In early September,the BPH resource areas mainly distributed in single rice of Anhui,Hubei and Guizhou Province.In mid September,the expansion of source areas was continuous,and mostly rice cultivated regions in Hubei,Guizh,Anhui and Zhejiang Province were the source area,even the northern part of Hunan Province.In late September,the middle and lower Yangtze River rice cultivated regions could provide BPH to Hunan Province,and the core district were located in Anhui,Jiangsu,Zhejiang,Hubei and Jiangxi Province.(2)In late rice,the carrying force for BPH immigrating into Hunan Province was northerly airflow,northeast airflow and east airflow,which the ratio were 30.85%、38.15%and 15.75%,respectively.East airflow that emerged in form of typhoon took BPH from Jiangsu and Zhejiang migrating Hunan Province,and northeast airflow was the main force bringing BPH return migration during the September and October.(3)In this paper,there were enough scientific evidences to support the idea that downstream and rainfall,cyclone and ceiling of the threshold temperature were the major stresses factors for BPH landing in August and September of Hunan Province,with the value of 25.23%and 27.64%to the total peaks.Besides,rainfall affected under the condition of the tropical cyclone was also the reason for BPH landing.Moreover,as well as WBPH in early rice,the ceiling of the threshold temperature of flying BPH in atmosphere was one of the factors for the BPH landing in late rice of Hunan Province after September. |
