Abstract: The larvae of Micromelalopha troglodyta were fed under both controlled and field conditions with leaves of the progeny of transgenic poplars carrying Bt genes planted in the field to evaluate the insect-resistance.The results showed that the highest revised mortality of 1~(st) larvae fed with leaves of transgenic poplars carrying Bt genes for 12 days reached (84.3%).The insecticidal capacity of transgenic poplars expressed the evident temporal dynamic:the revised mortality of 1~(st) larvae fed with leaves of 3 transgenic poplar clones FB45,FB51 and FB56 in June reached 56.9%～84.3%,but obviously decreased to 35.6%～45.1% in July and August,and again raised to 59.4%～80.8% in September.The sensitivity of the various instar larvae to transgenic poplars was different.The revised mortality of 1~(st)～3~(rd) larvae fed with leaves of transgenic poplars for 6 days reached 19.8%～25.4%,which had the significant difference with CK,but the mortality of 4~(th) and 5~(th) larvae had no significant difference.Transgenic poplar also greatly restrained the growth of most larvae,and it could greatly decrease the feeding and the rate of weight increase,which finally resulted in the death of larvae.