Abstract: Objective   To observe the acaricidal effect of the water extract of Xiushan sea mud on Demodex brevis and D. folliculorum.   Methods   D. brevis and D. folliculorum were obtained with modified scraping method. Each sample contained 30 or more alive Demodex which were evenly spread on the slides with 200 μl water extract of Xiushan sea mud at a concentration of 2.5，2.0，1.5，1.0 and 0.5 kg/L，respectively. With 10% sulfur emulsion as positive control and saline as blank control，each experiment group was carried out at the same time. Under room temperature of 20 ℃ and relative humidity of 70%，parasite death number was recorded at 5 min, 10 min, 20 min, 40 min, 1 h, 2 h, 4 h, 8 h, 12 h and 24 h. The acaricidal rate was measured and calculated by counting method. Demodex activity and morphology were observed using microscope.   Results   1.0～2.5 kg/L of the water extract of Xiushan sea mud increased the activities of both kinds of Demodex. D. brevis showed shrinkage, deformation, twisting and the bodies became shorter. The digesting vasoconstrictions of D. folliculorum also shrank and the stretching frequency of the tails moved faster. When the concentration of the sea mud extract decreased from 2.5 kg/L to 1 kg/L, the proportion of active movement of D. brevis and D. folliculorum decreased from 79.4%（27/34）、65.7%（23/35）to 68.9%（26/38）、53.8%（21/39）, and the activity time extended from 15 min, 20 min to 100 min, 104 min，respectively. The 0.5 kg/L of the sea mud extract showed no significant effect on the morphology and activity of both species of Demodex. When the concentration decreased from 2.5 kg/L to 1.5 kg/L，the time to kill both Demodex spp. extended from 2 h to 8 h. The extract at a concentration of 1 kg/L showed higher acaricidat effect to D. brevis than that of positive control（P＜0.05）, while there was no significant difference for D. folliculorum（P>0.05）. When the concentration decreased to 0.5 kg/L, the acaricidal effect for D. brevis and D. folliculorum remarkably reduced and there was no significant difference with the control groups（P>0.05）. The lowest effective concentration for both Demodex spp. was 1 kg/L. The values of 1 h median lethal concentration（LC50）of the sea mud extract for D. brevis and D. folliculorum were 1 913 mg/L and 2 131 mg/L，respectively.   Conclusion   The water extract of Xiushan sea mud shows acaricidal effect to human Demodex. The effect to D. brevis is slightly better than to D. folliculorum.

Key words:  , Water extract；Xiushan sea mud；Demodex brevis；D. folliculorum；Acaricidal activity