Abstract:The present paper deals with diapause of Eotetranychus populi (Koch).The results show that E.populi expresses diapause with fertile female adults,and it grows under long light (above 13 hours light per day) and produces diapause under short light (below 11 hours light per day). The threshold of photoperiod inducing diapause is at 12 hours light.The larva,protonymph are sensitive to photoperioodic changes,but the adults and eggs are not.Lower temperature (below 21℃) promotes the incidence of diapause and higher temprature (above 25℃) restrains it when they are subject under the photoperiod of 10 hours per day.