Abstract: Objective To investigate the mechanisms of Alternanthera philoxeroides （Mardus） Grisebach in inhibiting Oncomelania snails′ locomotivity and killing effect. Methods Uninfected snails were divided into four groups and exposed to an aqueous extract of A. philoxeroides and dechlorinated water （as control） for 12 h or 20 h, respectively. The activities of the Mg²⁺ adenosine triphosphatase （Mg²⁺-ATPase）, cholinesterase （ChE）, lactate dehydrogenase （LDH） and succinate dehydrogenase （SDH） in the head-foot muscles, centric ganglions, gills and liver of Oncomelania hupensis were analyzed using enzyme histochemistry technology and changes were observed under a light microscope. Statistical quantitative analysis of data of grey values was conducted on the computer-assisted image analyzing system （HPIAS-1000）. Results The color of stained ChE in the head-foot muscles, centric ganglions and gills of the snail lightened evidently， showing a decrease of ChE activity after snails were immersed in the extract of A. philoxeroides for 12 h or 20 h. Results of grey values at different stained parts of snail, measured by the computer-assisted image analyzing system， indicated that there was a significant difference （P<0.01） between the activities of ChE in the head-foot muscles （130.95±8.08，129.91±7.05）, centric ganglions （127.43±7.27, 126.78±7.38） and gills （121.38±7.31, 126.41±8.28） from snails exposed to aqueous extract of A. philoxeroides for 12 h and 20 h and the activities of the enzyme in counter-parts （64.65±8.54, 65.18±7.96, 57.86±6.57, 50.71±6.15, 88.96±6.78 and 89.86±7.01, respectively） from control group. The activities of Mg²⁺-ATPase also showed a significant difference （P<0.05） in the head-foot muscles （89.91±5.08）, centric ganglions （71.15±5.43） and liver （112.40±7.81） of the snail after 20 h of exposure against those in counter-parts （78.81±8.10, 60.09±6.05 and 95.50±8.35, respectively） from the control, but no significant difference （P>0.05） was shown on the activities of Mg²⁺-ATPase between the snails exposed for 12 h in extract of A. philoxeroides and those of control. No statistical difference（P>0.05） was found between the dechlorinated water group and the extract of A. philoxeroides group in the activities of LDH and SDH after 12 h or 20 h of exposure. Conclusion The extract of A. philoxeroides rapidly inhibits ChE, and then the activity of Mg²⁺-ATPase, which may suppress the release and utilization of ATP in the Oncomelania snails and finally causes death of snails.

Key words: Alternanthera philoxeroides, Oncomelania hupensis, Cholinesterase, Adenosine triphosphatase, Molluscicide