The small brown planthopper (SBPH) Laodelphax striatellus (Fallén) is a very important agricultural pest which can cause major harm to rice crops by acting as a vector of the rice stripe virus (RSV) and rice black streaked dwarf virus (RBSDV). In this study, the population dynamics of SBPH and its viruscarrying rate were systematically investigated and measured in ricewheat fields (rotation treatment vs. nonrotation treatment) in Shandong Province. The results indicate that (1) a higher SBPH density was found in the ricewheat rotation regions than in the nonrotation treatment, so it is presumed that SBPH favor the ricewheat rotation regions; (2) only RBSDV was detected in the SBPH from wheat fields, whereas both RBSDV and RSV were detected in SBPH from rice fields; (3) different viruscarrying rates were found between lighttrapped SBPH and the local SBPH population in Ningjin County; and, (4) from a total of 1 268 individuals tested, only one SBPH simultaneously carried both RBSDV and RSV, which indicates that SBPH can simultaneously carry both viruses but that such

individuals are relatively rare.