Study On Light-Trapped Behavior Of Sogatellla Furcifera (Horvath) And Nilaparvata Lugens (Stal)

White-backed planthopper (WBPH), Sogatella furcifera (Horvath) and brown planthopper (BPH), Nilaparvata lugens (Stal) were major harmful rice pests in both temperate and tropical regions of East and South Asia. Both two species of planthopper have long been problems which threaten the increased production of high quality, high income in China. Because of its long-distance migration, it is difficult to accurately forecast the occurrence due to this seasonal fro and to migration. Depending on its phototaxis, light trap was an important tool to monitor rice planthopper population dynamics in the past many years. It was not only contributing a lot in the study migration of rice planthopper in traditional methods, but also played an irreplaceable role in the modern techniques. Besides, light trap was also an important component in the integrated pest management. However, the studies about flight to light behavior of rice planthopper are still very lack. Hence, the study on the flight to light behavior of rice planthopper will be beneficial for the prediction and suppression of these pests in southern China and other parts of the country.Firstly, the trap efficiency of LED lamps with different wavelengths and traditional black lamp was compared, the special lamp wavelength which response strongly was determined. Besides, the weather factors on captures of rice planthoppers were also discussed. Then, the temporary inhibition of sation-keeping response to light in migratory rice planthoppers was investigated, and the population migratory characteristics of WBPH and BPH from light-trap catches was analyzed. Secondly, the theoretic flight to light paths of rice planthopper in different migration period was suggested combined with the trap catches from different height light traps and different direction of sticky plates. Finally, the relation between take off and phototactic rhythm of rice planthopper as well as the female biased flight to light behavior were discussed.1. Effect of light colours and weather conditions on captures of WBPH and BPHTo study the phototactic responses of white-backed planthopper, Sogatella furcifera (Horvath) and brown planthopper, Nilaparvata lugens (Stal) to different wavelengths, four colors of light traps (blue, green, yellow and red light-emitting diodes) were placed in the same rice field along with a traditional black light trap. This study revealed that S. furcifera and N. lugens are more attracted to blue and green lights than that to yellow and red lights. During the 24 nights, compared to the black light trap, the blue LED trap could catch more rice planthoppers at 17 nights. Furthermore, catches of other species (moths and beetles) were substantially reduced in blue LED light traps. Multiple regression models were developed to assess the effect of weather factors on light trap catches of rice planthoppers. Rainfall and mean air temperature at a night mainly affected light trap catches of S. furcifera. Higher rainfall and lower temperature increased light trap catches of S. furcifera. However, wind speed was the main factor affecting the catches of N. lugens, and the lower incidence of catches was found in the night when wind speed exceeded 3.08 m s-1. S. furcifera may be flying against wind at light wind nights by 0.3 m s-1 to 1.5 m s-1, whereas N. lugens may be flying down at strong wind nights by 1.5 m s-1 to 3.08 m s-1. Relative humidity did not significantly influence on trap catches. Consequently, light wavelengths, precipitation, average temperature and wind should be considered when monitoring rice planthoppers by light traps. Therefore, the blue LED light traps are worth using for monitoring planthoppers.2. Temporary inhibition of station-keeping response to light in migratory rice planthoppersThis study aims to determine whether or not migratory rice planthoppers [Sogatella furcifera (Horvath) and Nilaparvata lugens] in South China temporarily inhibit their station-keeping response to light during migration and to elucidate whether or not these insects respond to light traps located in their native habitat. Results of mark-release-recapture experiments revealed that the overall recapture rate was very low (0.028%) and that almost all emigrating macropterous adults did not respond to local light traps. The population dynamics of planthoppers in the light traps were not synchronous with that in the field. The peaks of planthoppers caught by light traps appeared when the low-level wind jets at 850 hPa isobaric surfaces, and these catches were almost immigrants from distant places. The macropterous planthopper adults in the field can be passively dispersed when their take-off was suppressed by precipitation and then would respond to light traps at night. These results show that migrating planthoppers are not distracted by light traps in their native habitat. This study provided interpretation for the definition of migratory behaviour.3. A preliminary study on the behaviour mechanism of phototactic response of rice planthoppersThe behavior characters of rice planthoppers around the trap lights were discussed in detail through systematic investigation of population density and female ovarian maturity types.(1) The immigration period of WBPH and BPH in Jinhua rice field were before 10th and 20th August; the emigration period were after 11th August and 4th September,2011. The species of rice planthoppers in light traps were consistently by the high lamp and the low lamp, but the number of rice planthoppers caught by upstairs lamp was far much greater than that by ground lamp.(2) Without considering the influence of external factors, whether in immigration or emigration period, both WBPH and BPH tend to respond to the high lamp, this result was caused by the phototaxis lag effect of rhythm responding to a trap light. And the phototaxis lag effect time of rice planthoppers is about 6.7s-28s.(3) Rice planthoppers was not passive free-faller when falling in immigration period, they was the first throw themselves on lamp before drop to rice filed, and the theoretic flight to light path was suggested, the take off path of planthoppers was showing a certain angle.(4) The correlation between the light-trap catches and the rainfall was highly significant, and was significant with the minimum temperature. Heavy rainfall had a great impact on the behavior of phototactic response of WBPH, the result of phototaxis lag effect was disrupted; lower temperature can seriously affect the planthoppers’ take-off.4. Effect of rainfall on the take off behavior of rice planthoppersThe effect of rainfall on the take off behavior of rice planthoppers was studied by observation of captive insects. Results showed that the take off behavior of rice planthoppers have obvious daily rhythm when there were no precipitation during night, showed "double-peak at dawn and dusk", and the dusk-peak is the highest peak and the dawn-peak is relatively small. While it showed "multi-peak" when there were precipitation during night. The adult take off number at night showed a highly significant positive correlation (R=0.694*, P=0.026) with precipitation, it suggested that rainfall somehow trigged the take off of planthoppers during night. However, the adult take off number of planthopper at dawn showed a highly significantly negative correlation (R=-0.740*, P= 0.014) with precipitation, it suggested that the rainfall trigged the palnthoppers original planed take off at dawn were advance at night, resulting the take off amount declined at dawn.5. Mechanism of rhythmic and female biased to the lightThe phototactic rhythm was studied by hourly light trap catches during night. Results showed that when there was precipitation at night, there were some phototactic rhythm types:dusk-peak, dawn-peak, midnight-peak, before midnight-peak, after midnight-peak, all night-peak and midnight-dawn peak. It is showed "muti-peak" when there no precipitation at night. It suggested that there were not obvious correlation between take off and phototactic rhythm, this also conformed the population in light trap almost were immigrates.The planthoppers reveals female biased during the light trap in the field from 2009 to 2013, the light captured more females through the occurrence period. While the sex ratio of the natural adult population was 1:1 by field surveys.6. Case studies:flight-to-light behavior used in trajectory analysisThe population dynamics and characteristics of BPH in Yongfu were studied through systematic investigation and female ovarian maturity types in 2012. The main trap catch peaks were observed each hour using infrared camera during night, and determined when BPH landed. The source areas and landing areas of BPH from 26 to 28 July were analyzed by calculating trajectories with NOAA ARL HYSPLIT model.The following results were obtained:the landing areas from 26 to 27 July were Sanjiang and Longsheng that about 100 km away from Yongfu due to air temperature limitation, and the secondary landing areas were northwest Guizhou; and the landing areas at 28 July were west Hunan.The source areas from 26 to 28 July were all in the southern regions not far away from Yongfu, the longest areas were at Guigang less than 200 km, and the nearest areas were at Liuzhou less than 50 km.