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
Abstract: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.