Abstract: Based on the indoor inoculation test conducted from1996 to 1998,the characteristics of transmitting phytoplasma by Halyomorpha picus associated with paulownia witches′ broomwere compared between insect groups (adults and nymphae) of reared pathogen acquisition (RA) and naturally pathogen acquisition (NA).The results showed that the rate of pathogen transmission to paulownia seedlings by third and fourth instar nymphae of RA was 61.7% and 41.4%,which weremuch higher than that by nymphae of NA (16%).For adults,the transmission rate was 14.1% of RA which was also higher than that of NA (4.5%).Theminimumincubation period (MIP) of pathogen in vivo were 34 days and 45 days for third and fourth instar nymphae and 219 days for adults (RA),that for nymphae and adults (NA) were 243 days and 257 days respectively.The seedlings inoculated in June showed symptomof disease in the same year,while that inoculated in July showed symptomof disease in the next year.The incubation period (IP) had a positive relation with successive disease rate.For third instar nymphae,the equation of relation was y=0.8472x+23.044(R2=0.8743) and relevant LP50=65.40 days,that for fourth instar nymphae was y=0.759 x+29.022(R2=0.8019) and LP50=66.472 days.The feasibility of using RA nymphae for early assessment of paulownia genetic breeding against witches′ broomwas discussed.