Occurrence of Golden Apple Snail, Pomacea canaliculata (Lamarck), in Paddy Fields and its Management in China

Yu Xiaoping1, Li Zhongfan2, Lu Zhongxian1, Sun Leping3, Chen Jianming1, Zhen Xusong1, Xu Hongxing1
1 Institute of Plant Protection, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021
2 Science and Technology Association of Ouhai, Wenzhou 375005
3 Agricultural Bureau of Ouhai, Wenzhou
E-mail: luzx@public.hz.zj.cn

Abstract: This paper reviews the occurrence and damage situation of golden apple snail, P. canaliculata (Lamarck), in paddy field in China: its control methods and management strategies used by Chinese farmers. It also introduces briefly the advances and future prospects of research and management on golden apple snail.

Key words: Golden apple snail, Rice, Occurrence and damage, Management, China 

Introduction
The golden apple snail (GAS), Pomacea canaliculata (Lamarck) (also written as Ampullaria gigas Spix in many Chinese literatures) is indigenous to tropical and temperate South America, and was imported into China in the 1980s as food. Since the taste of this snail meat was not acceptable for many Chinese people, some of them were disposed into wild and began to attack rice, Zizania, and other graminaeous plants. The GAS was recorded in many provinces in China including Guangdong, Guangxi, Hainan, Taiwan, Fujian, Yunnan, Shichuan, and Zhejiang, usually occurring in the southern of latitude 30°N in China. In Zhejiang province, the GAS seriously occurred in the paddy fields of Wenzhou and Taizhou area where the temperature usually is above 0°C in winter, however, in Ningbo area which is much cooler in winter than above two areas, the GAS seriously attacked the new tillers of Zizania caduciflora which is a vegetable crop of similar shape to rice. As recorded in many literatures, the GAS was imported into many cities in China as a new rearing animal, and then disposed into canal or fields because of its unacceptable taste to Chinese people. It became a pest on rice and other aquatic crops, which became suitable habitats and hosts. It was found that the GAS adults tended to settle or feed on water hyacinth (Eichhoraia crassipes Sloms) and Pistia stratiotes in the river or irrigation canal, and spread to other places with these aquatic plants. It was recorded that GAS spread toward the north 8~10 kilometers per year.  

Occurrence and infestation  
Back in 1988, the GAS was firstly recorded in 37 counties of Guangdong province on rice. The damaged area infested by GAS was about 1700 hectares. Later, GAS caused more serious damage in a wider area, with a damaged rate from rice seedling and tillage of 4~7%, especially in the high moisture area. The GAS was recorded to feed on other paddy crops, including lotus, adlay millet, taro, and Zizania. However, the damaged area of these crops is generally in small scale.
The GAS occurred in incomplete two generations per year, including over-wintered and 1st generation. The shell diameter of over-wintered GAS adult is about 2~3cm, and usually its progeny caused two peaks in early-May and late-May respectively in paddy fields. GAS caused damage on the seedling of early-season and late-season rice in April and August, especially in direct-sown rice. The feeding amounts and damage rate of GAS on rice increase with the increase of GAS shell diameter. The data show that the GAS of >20g infested and killed 38~52 seedlings and the GAS about 12g could damage 20~26 seedling. Only 3~13 rice seedlings were killed by the GAS < 5g during 2.5~3 leaf stage. The damage of GAS becomes less, as the rice plant grows more mature.
The GAS was very sensitive to low temperature (1~2°C or lower temperature), and one-day exposure to 1~2°C temperature caused 100% mortality. However, no mortality was found when the GAS exposed to 3~5°C for 30 days. In early or mid-October, the GAS buried into the paddy soil 2~3cm for over-wintering due to the cool temperature and dry soil. Some GAS could be found in irrigation canal or river for over-wintering. The experiment on 1~2o C temperature treatment indicated that 50~75% GAS survived if they bored in the soil.

Current methods of snail control
The table lists methods currently adopted by Chinese farmers for controlling GAS, including cultural control, natural enemies and molluscicides. Among these, the most widely used measures during off-season are: cleaning weeds in irrigation canal, hand-picking or crashing adult shells in canal and paddy fields to reduce the GAS density. In Wenzhou, farmers used ducks to feed on young snails in the paddy fields and canal. Data showed 50% mortality for current generation and 85% density reduction for first progeny using 300 ducks per hectares in paddy fields and neighboring canals as compared to control. Chemical control is most likely to be used by farmers when other methods are not effective. Among chemicals currently used by Chinese farmers are 70% Bayliscide, 6% Metaldehyde, 98% Padan, 98% Copper sulfate, 65% PCP-Na and camellia seed cake etc. 70% Bayliscide and 65% PCP-Na were tested to be more effective in controlling snails.  

Strategies and measurements for controlling golden apple snail (GAS) adopted by farmers in China.

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