Abstract: The nature of the biotype of the brown planthopper (BPH) immigrating into rice field was recently studied. Results indicated that no obvious differences in virulence, rate of survival, honeydew excretion, zymograms of the esterase isozyme had been found between the immigrant populations and the primitive population of BPH on susceptible cultivar Nanjing 11. Therefore, the immigrant populations of BPH were still of biotype I in Jiang-Huai rice region, but their virulence to Mudgo had developed a lit tle bit. The virulence to Mudgo decreased down to scale 1.0 when the BPH biotype fed on susceptible varieties for 8 generations, showing its virulent unstability.

Key words: BPH, biotype, monitoring