Abstract: Objective To investigate the distribution of Oncomelania hupensis in the snail-obtainable soil of a waterway network, and the theoretical guide to finding and killing snails was provided. Methods Twenty soil samples were taken using systematic sampling and environmental sampling methods from three plots of snail-obtainable regions within Xingbang village, Liantang town, Qingpu district, Shanghai, China, in May 2016. Oncomelania hupensis snails on the surface of the soil were picked up and counted; then three pieces of specimens (500.0 g per piece) were taken from each soil sample, and the snails in the soil specimens were collected for counting after being washed with a double-layer sieve. The Kolmogorov-Smirnov D test was used to perform normal distribution analysis for the snails in the soil. Statistical parameters of aggregation tendency were used to describe the snail distribution. The Wilcoxon rank-sum test was used to compare the mean number of the snails among the three plots. The goodness-of-fit test was used to determine whether the snail counts follow a negative binomial distribution. Results Sixty pieces of soil specimens were taken from three plots of Zhujiadai River, Qingsonggang, and Duantoubang in Xingbang village, and they were washed for collecting adult snails in the soil. The Kolmogorov-Smirnov D test showed that the numbers of the snails were not consistent with normal distribution (skewness coefficient=1.03, kurtosis coefficient=0.71, D=0.167, P<0.001). The Wilcoxon rank-sum test showed no significant difference in the snail count between the three plots (Z=0.405, P=0.815). The mean of the snail counts was greater than the median in each plot, and the kurtosis and skewness coefficients both deviated from 0, indicating that the snail counts followed a positively skewed distribution. The variance was greater than the mean, representing an aggregation distribution; the goodness-of-fit test showed that the snail counts fitted a negative binomial distribution (χ²=1.844, P=0.765). Conclusion The distribution of O. hupensis in the soil is consistent with that on the soil of the snail-obtainable regions, which is clustered and positively skewed, following a negative binomial distribution rather than a normal distribution.

Key words: Oncomelania hupensis, Aggregation tendency, Negative binomial distribution, Degree of fitting

摘要： 目的 研究水网地区有螺泥土中钉螺分布规律，为查螺、灭螺提供理论指导。方法 采用系统抽样结合环境抽查法，2016年5月在上海市青浦区练塘镇星浜村有螺地区的3个地块中分别采集土壤样本20块，捡取计数泥土表面钉螺后，每块土壤分别抽取3份（每份500.0 g）样品，采用双层箩筛水洗获得钉螺并进行计数。采用Kolmogorov-Smirnov D检验进行土壤中钉螺的正态分布检验；采用集中趋势统计指标对泥土中钉螺分布情况进行统计学描述和分析；采用非参数Wilcoxon秩和检验对3个地块泥土中钉螺均数进行检验；采用负二项拟合优度检验钉螺是否服从负二项分布。结果 在星浜村的朱家埭河、青松港及断头浜3个地区共采集60份样品，经清洗获得泥土中钉螺成螺。正态性检验显示，钉螺分布不符合正态分布（偏度系数=1.03，峰度系数=0.71，D=0.167，P<0.001）；非参数Wilcoxon秩和检验3个地块泥土中钉螺数差异无统计学意义（Z=0.405，P=0.815）；每个地块泥土中钉螺的均数>中位数，峰度系数和偏度系数偏离0，钉螺分布属正偏态分布；方差>均数，属聚集性分布；负二项分布拟合优度检验服从负二项分布（χ²=1.844，P=0.765）。结论 有螺地区土壤中钉螺与泥土表面钉螺的分布一致，属聚集性、正偏态分布，服从负二项分布。

关键词: 钉螺, 聚集趋势, 负二项分布, 拟合优度