关键词: 钉螺, 聚集趋势, 负二项分布, 拟合优度

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