Complex influence of rice variety, fertilization timing and insecticide on population dynamics of Sogatella furcifera (Horvath), Nilaparvata lugens (Stal) (Homoptera: Delphacidae) and their natural enemies in rice in Hangzhou, China

The complex influence of rice variety, fertilization timing, and insecticides on the population dynamics of Sogatella furcifera (Horvath) and Nilaparvata lugens (Stal), and their natural enemies was studied in rice in Hangzhou, China. In the early season, S. furcifera adults immigrated to japonica Xiushui I I (XS 11) in a much higher density than to indica-japonica hybrid Xieyou 413 (XY413), which resulted in a higher density of the egg population of successive generations in XS11, while the peak density of the population peak of the 2nd generation in XY413 was higher due to a higher growth rate. In both of the rice varieties, spraying organic phosphorous triazophos in mid-season (during the 1st generation of the planthoppers) induced a population resurgence of the 2nd generations of S. furcifera and N. lugens. The main mechanism for the resurgence was the stimulation of reproduction of the 1st-generation adults and reduction of the density of predators, which in turn increased the survival of the planthoppers. Plots that were fertilized early attracted more N. lugens immigrants, but did not necessarily attract S. furcfera. Reproduction of the S. furcifera immigrants was enhanced by early fertilization of the fields of both rice varieties. The negative correlation between population Growth rate from the 1st to the 2nd generation of S. furcifera and the density of spiders during the same period demonstrates the potential of predators in the natural control of rice planthoppers.