| Laodelphax striatellus (Fallen)(SBPH) spread in temperate zones such as East Asia, Southeast Asia, Europe and North Africa, and can overwinter safely in these areas. In China, it is distributed over the country, mainly in East and North. Its damage to rice includes not only direct sucking damage, but also transmission of various virus diseases of rice. Because of the complex effects of global warming, the change of cropping system, and the increase of the susceptive rice varieties, etc., SBPH had been outbreaking and become a serious pest in China at this time. In order to deal with the aforementioned issues, field observations, light trap catches, anatomy of the female ovary, trajectory analyses and artificial climate simulation have been used to study the population dynamics and long distance migration in spring, the effects of high temperature on population density in summer, and the natures of overwinter and diapause. This research utilizes rice production data for biological research and forecasting of SBPH. The main results are as follows:1. The observations of overwintering and migration for seasonal host plant displacement from overwintering host wheat to the summer host rice had been performed. SBPH overwintered as3-5instars (mainly as4th instar) under the wheat, weeds and rice stubble from October to the next March. After the heading of wheat huge of the macropterous adult of SBPH emigrated, from the end of May to the mid June, mass macropterous adult immigrated to rice fields and weeds, which injury to rice and transmit the virus disease. Light trap catches were collected per hour interval indicated that, during the emigration period, SBPH take-off show a bimodal curve at dawn and dusk, mainly in the dusk, while during immigration period SBPH may immigrate at every hour after19:00, and majority before midnight. The source regions of the immigrant was analyzed using the trajectory analysis, which proved that the immigrant may come from the north of Jiangsu, northwest of Anhui and south of Zhejiang and Fujian fly along with the variation of wind direction on850hpa.2. The overwinter diapause characteristic had been researched since May2010. Seven treat combinations, low temperature22℃, high temperature30℃and photoperiod4、8、10、12、16h were set under artificial climate cases for testing the effect to induce the diapause of SBPH. The results showed that the diapause of SBPH exhibited as the low temperature short photoperiod diapause type, the photoperiod range of inducing diapause was quite narrow, only between8and10h photoperiod could have100%individual diapause; while at4and12h photoperiod, the percentage of individual diapause were reduced to67.85%,51.02%respectively; this value down to0%when the photoperiod increased to16h. But at high temperature30℃and long photoperiod16h the nymphs of SBPH had no reaction to photoperiod, and its individual diapause percentage was0%. According to the calculation, the critical photoperiod of SBPH was13h20min, and in Nanjing it happened around12th Sep.3. The nature overwinter population of3-5th instar nymph were collected in Nanjing in Dec2009, The completion of diapause was tested under20℃,30℃and different light periods. The results showed that under all the treatments the development and durations of different instar all returned to normal. It can be inferred that diapause of SBPH, which was induced since September in Nanjing, experiencing the winter natural low temperature above0℃for about2months, had completed and entered the dormancy stage (or the post diapause stage).4. Telemetry logger was employed in the experiment in Zhejiang,2009-2010. The difference between the normal air temperature and the microclimate of the habitat niche of SBPH which is located at the base of rice bushes10cm above ground was recorded systematically. The conversion tables including included three weather types and ten-days average temperature differences between microclimate and atomosphere from July to Sep were built. The main results were:max air temperature> max rice bushes temperature>average air temperature>average rice bushes temperature, which may provide real conversion and the scientific basis for research and production forecasting.5. The methods of artificial simulated high temperatures and various photoperiods were employed for tested its effect on development and possibility of summer diapause of SBPH. The results indicated that the max temperature≥30℃in variable day temperature may restrain the nymph’s growth and the development duration was significantly longer, but during the fitting temperature range there are no differences. Under constant high temperature30℃there was no differences among various photoperiods. Therefore the variable high temperature only prolonged the development duration of SBPH, but had no indication of diapause. The main basis were (1) Under various combinations of temperature and photoperiod conditions, SBPH had no response to long photoperiod, however the high temperature and long photoperiod were the main factors which induced the summer diapause almost in all of the known insects.(2) Although Under the max temperature≥30℃the duration of the nymph may prolong to2.1-2.75times, butthe impact of different instar was uniformly, and no particularly long duration instar was found. In other word, there was no critical diapause instar. Therefore, max temperature≥30℃can only affect the survival, breeding and development of the population, but not the summer diapause.6. The differentiating of SBPH nymph whether diapause or non-diapause was as follows:at22℃1-5instar nymphs developmental duration>40days,100%of planthopper nymphs diapause groups; between25-40days, part-diapause;<25days, non-diapause. |
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