The Takeoff And Dispersal Behavoirs Of Laodelphax Striatellus (Fallén) And Spatio-Temporal Dynamics In Fields

The small brown plant hopper (SBPH), Laodelphax striatellus Fallen has been a pest severely damageing the rices, for which short-range dispersal is dominating, but there are evidences that it has long-range migration. The takeoff and dispersal behaviors and spatio-temperal dynamics in fields are very important for its occurrence, outbreak and spreading virus, so we studyed those in Yangzhou and Tongzhou in 2005 and 2006 respectively.The takeoff and dispersal behavior of SBPH and its ralation to factors like the density of macropterous form, wheather, intensity of light and ovarian development were studied by means of field observation, cage experiment and ovary dissection in Hanjiang borough of Yangzhou city from the early July to the late September on 2005. The results show that SBPHs are mostly take off after the sunset, and there are a certain threshold density and a optimum lux range for the takeoff. It also shows the oogenesis-flight syndrome to a certain extent.The first generation of SBPH in wheat fields is the important period when the population enlarge and disperse to rice fields, and one of key periods for controlling it. In order to manage the insect more effectively,and further study the spatio-temporal distribution of its population,geostatistical methods were used to analysis the spatial structures of the first generation of larval SBPH in the time series.Fitting the semivariogram models for the every instars of larval SBPH in the wheat field,the spherical model and the gaussian model were best for the majority situations while only a few datasets best fitted the hole effect and the exponential model. Then discovered some relations between the characteratics of the semivariograms and the density of larval SBPH or envirement factor:the major and minor range have no significant correlation with the density,either is close to a corresponding constant; the nugget was positively correlated with the density because of the existing of the scale effect,in order to eliminat the scale effect,divided the nuggets with the sills (the sill theoretically equal to the variance of the sample),then got a new parameter the spatial random intensity (nugget/sill),which fitted a cubic polynominal curve with the density;Semivariograms were anisotropic because the distance between wheat plants was different from the distance between rows. Arrayed the prediction surface maps of the larval SBPH density,which created with the Odinary Kriging method,compared and analysised the spatio-temporal distribution that had been visibly displayed in the maps.Resulted that the spatio-temporal distributions were relatively stable.Considered that the ample food,the island-like habitation and the poor movement ability of larval SBPH itselt were the main reasons for this situation.Besides,some secondary factors include predator in the field also had effect on the distribution of the larval SBPH population.Experiments were conducted on grid samples in two rice paddys: the one is a 50m by105m rice paddy in Hanjiang borough of Yangzhou city from july 20th to September 25thin 2005, the other a 40m by 60m rice paddy in Tongzhou country from july 16th toSeptember 29th in 2006. Geostatistical methods were used to analysis spatio-temporaldynamics of Laod- elphax striatellus Fallen. For all semivariograms of the small larvae,large larvae and macropterous adults in 14 investigates in Yangzhou, there were 20,13 and9 semirariograms best fitted the spherical model,the exponential model and the gaussianmodel respectively, for those of macropterous adults in 16 investigates inTongzhou, thenumbers were 7,5,4. Majority of the datasets showed significant anisotropy, and thedirection of which greatly correlated with plant row direction of the rice paddy. Anisotropyof macropterous adults showed strong randomicity but the larvae did not. Most of thedatasets exhibited low or medium spatial dependence, thereinto the relative nugget of smalllarvae was ruleless caused by the oviposition of macropterous adults, and the relativenugget of large larvae fitted a negative logarithm curve with the density, while that ofmacropterous adults was always as big as nearly up to 1. Created the SBPH distribution interpolation maps with Ordinary Kriging method and analyzed them in the time order, found that use of the pesticide significantly effectted the distribution of SBPH, and the larvae had a relative steady-going spatial distribution while macropterous adults did not and there were signs that they dispersed in the peak time. The spatial structure and distribution of larval and adult SBPH depended on the movement abilities of themselves, factors such as the use of pesticide and oviposition behavior of adults also had an effect on those.