Abstract：
Virulence variation in three host related popula ti ons of brown planthopper (BPH), which differed in virulence and had been reared on rice variety TN1, Mudgo and ASD7 for 82 generations respectively, was studied with honeydew excretion of female adult in 48 h. Honeydew excreted by avirulent BPH population (TN1 population, most individuals are avirulent, called T population), or virulent BPH populations (Mudgo or ASD7 populations, most individuals are virulent, called M or A), on susceptible and resistant varieties were weighed, and the resulsts showed that the susceptibility and resistance of host pl ants interacted with the virulence of BPH. BPH with different virulence should be reared on resistant varieties to observe evident difference, so virulence of BPH under different treatments to resistant varieties was tested to study virulence variance. Mean virulence in F1 populations was an intermediate value and near to that of virulent parent, and the variance of honeydew distribution in F1 populations was obviously bigger than that of avirulent parent and near to that of virulent parent. It seemed that virulence was dominant to avirulence. When compared with those in F1 populations, the mean virulence in F2 populations performed few changes in the treatment T ♀×M ♂ , and was significantly bigger than that in the treatment A ♀×T ♂. The variance in F2 populations was obviously smaller or bigger but not significantly than that in F1 populations. Based on the above results, it is concluded that there were no new genetic segregations in F2 populations compared with F1 populations.
2004, Vol. 18 
