A systems analysis approach to brown planthopper control on rice in Zhejiang Province, China. I. Simulation of outbreaks.
A simulation model of the population dynamics of the delphacid Nilaparvata lugens on rice in Zhejiang Province, China, was constructed using field population data from this region together with information from the literature. The purpose of the model was to assess the performance of the management options of N. lugens with a view to improving current practices. The model is described and its predictions are compared with independent sets of field data. For 10 data sets, representing a range of N. lugens densities, the time of the peak in the population was predicted within 5 days in 9 cases (accuracy of observations ±5 days). The density of the population at its peak was predicted within 20% of the observed in 7 cases. Compared with the regression models currently used to predict N. lugens outbreaks, the simulation model was much more accurate when tested with the same data; regression models use only density of N. lugens early in the season. The simulation model also took into account seasonal temperatures, the effects of transplanting time, and the pattern of immigration of N. lugens into the crop. Model parameters were varied within realistic limits in order to determine the sensitivity of the model. The model was sensitive to changes in the mortality of N. lugens, but a constant daily mortality rate, representing the effects of natural enemies, was sufficient to predict field population changes. Summer and autumn temperatures, rate and pattern of immigration of N. lugens, and transplanting time all had a significant impact on the size of modelled populations. It is predicted that a cool summer, warm autumn, early transplanting time, and short concentrated period of immigration, should result in damaging populations of the pest even when the rate of immigration is moderately low.