入侵移栽稻田的福寿螺卵块空间分布型及其抽样技术

福寿螺Pomacea canaliculata Lamarck是重要外来入侵有害生物,严重危害水稻苗期至分蘖期的秧苗植株.为明确福寿螺在水稻田的空间分布,以1、4丛水稻为取样单位(样方)调查了14块移栽稻、每块田300个样方的福寿螺卵块密度,并利用聚集度指标法、Taylor幂法则和Iwao的M-m回归法进行分析.结果表明,移栽稻田中的福寿螺卵块主要呈聚集分布,部分田块呈随机或均匀分布.根据福寿螺卵块的分布型,通过计算抽样时间和抽样准确率的关系、不同样方和误差条件下的理论抽样数,确定以准确估计田间卵块密度为目标的最佳抽样方法,以横(行)向平行线跳跃法间隔30～45行调查1行,共调查6行90个4丛水稻样方,即两人以常规速度按上述方法取样18min以上,可达85%以上的取样准确率.

Spatial distribution pattern of egg masses of the golden apple snail, Pomacea canaliculata Lamarck, and a sampling plan for their detection invaded in subtropical transplanted rice fields

The golden apple snail, Pomacea canaliculata Lamarck is a disastrous invasive gastropod species intentionally imported by humans for economic gain. While its husbandry has been abandoned due to small market demand, it has continued invading rice fields since 1980s in tropical and subtropical Asian rice ecosystems. The lack of information regarding its spatial distribution has resulted in an absence of suitable field and regional scale sampling techniques to control and predict its dispersal. We counted the snail egg masses in 300 uniformly-arranged sampling units in each of 14 transplanting rice fields on the southeastern coast of Zhejiang, China. This was conducted using one of 2 types of sampling units with 1 or 4 rice hills per unit. The results showed that the individual egg masses were found to have an aggregative distribution pattern in most cases. Patchy distribution of still water in the rice fields might have been the dominant factor causing this pattern. We propose an experientially optimal sampling plan of parallel jumping sampling units of 4 hills along 15 units per row, conducted over 6 rows at row intervals of 30-45 for a (grand) total of 90 units in a field. Such a sampling plan will achieve a precision of 85% or more at a cost of 18 minutes between two people per rice field.