水网地区低密度钉螺自然增长情况

FIELD OBSERVATION ON THE POPULATION FLUCTUATION OF ONCOMEIANI A SNAIL AT LOW DENSITY IN PLAIN REGION

通过1987—1990年在无锡、如东、如皋3个市县的现场实验和河沟钉螺调查。发现低密度钉螺的消长与环境因子密切有关,只要环境适宜,即使留下1对钉螺,也能大量繁殖增长。实验沟放置有1、5和10对钉螺的螺笼经3年后,钉螺密度各增长了171.9倍、69.5倍和28.4倍。其螺口数分别增长了354倍、135倍和75倍,其中2条积水沟的1对钉螺组螺口数增长543和426.5倍。在现场1条水沟钉螺密度增长了34倍,1条河钉螺密度没有增长,但都没有自然消亡。提示当“基本消灭”或“消灭”以后,应重视低密度钉螺的清查,坚持长期监测,一旦发现钉螺,要及时杀灭。

Field observation on the population fluctuation of Oncomelana snail at low density was carried out in the ditches and rivers in Wuxi,Ludong and Lugao counties (or city) from 1G87 to 1990.The results showed that the environment of the observed places is an important factor in the population fluctuation of the snails at low density.When the environment is appropriate,even one pair of the snails may multiply to a large populationResults of successive observation for 3 years on 1,5 and 10 pairs of snails within nylon cages in ditches showed that the density of the snails increased by 171.5,69.5 and 28.4 folds respectively and the population of the snails increased by 354,135 and 75 folds respectively.The population in 2 of the observed ditches with one pair of snails each even multiply by 543 and 426.5 folds.While in natural field condition,the population fluctuation of residual snails varied in different places.In one ditch it multiptied by 34.7 folds,but in another river the population almost unchanged.No natural elimination of snails could be found in all observed places.It was suggested that the snail surveillance should be conducted persistently and any snail once be found,it shou'd be timely eradicated.