Occurrence pattern of Spodoptera litura in Hunan and its prediction methods
The occurrence regulation of Spodoptera litura was studied according to the continiuous years's data investigated in tobacco fields and weather data of Chenzhou and Ningyuan in Hunan. Results showed that generations of Spodoptera litura are 4–4.5 with the effective accumulated temperture per year and the actual generations of Spodoptera. litura is in accordance with the predicted generations in Hunan Province. The sources of Spodoptera litura in early stage of the year were migration pest, there were four occurrence stages in a year according the properties of pests sources, the number of trapped moths from April to June is significantly correlated with the number in March, the forecasting model is ŷ = 233.54 + 112.44x<inf>4</inf> (r = 0.815<sup>∗</sup>, n = 8). The number of trapped moths from April to June is significantly correlated with the daily average temperture of January (reliability degree was 90%), the forecasting model is ŷ = −1410 + 350x(r = 0.595, n = 9). The number of trapped moths of Agrotis ypsilon at its major migration stage (February-April), which synchronously migrated with Spodoptera litura, is significantly correlated with the number of Spodoptera litura in its major migration stage (April-June), and it provide data for the prediction of occurrence trend of Spodoptera. litura. The damage percent is significantly correlated with the number of Spodoptera litura per 100 plants, and the number of Spodoptera. litura per 100 plants at normal control plots as x<inf>1</inf>, the damage percent as y, r = 0.977<sup>∗∗</sup> (n=10); the number of Spodoptera litura per 100 plants at observed plots as x<inf>2</inf>, the damage percent as y, r = 0.974<sup>∗∗</sup> (n=10).