| Country or region name |
Taiwan, R.O.C. |
| Organism group |
other animals |
| Order name |
Mesogastropoda |
| Family name |
Ampullariidae |
| Species name |
Pomacea canaliculata |
| English common name |
golden apple snail, apple snail |
| Substantially same species (synonym) |
|
| Year of invasion or detection |
1979 |
| Native region |
South America |
| Situation of establishment |
Category 2: Settled after 1951 |
| Taxonomic description |
| |
| Expansion of distribution area |
| Golden apple snail is now widespread in Taiwan. Apple snail firstly
was introduced from Argentina into Taiwan in 1979 for the purpose of human
consumption. However, consumers did not react as enthusiastically as snail
farmers did due to the texture of snails flesh. Additionally, only 18%
edible part of apple snail makes it difficult to be processed as canned
food. As the domestic and export market vanishing, snails were discarded
and entered into local ecosystem. It then spreads out through waterways
and irrigation canals, quickly became a major pest of aquatic crops. The
damage on rice was firstly noticed in Kaohsiung and Pintung in 1982. Now
the apple snail is commonly seen in the irrigation waterways in Taiwan,
and is one of the most destructive pests for aquatic crops. |
| Environmental impact |
| Apple snail has a gill and a lung-like organ and therefore can survive
in and out of water. It can withstand periods of drought for several months
by closing its operculum and bedding down in the soil. It becomes mobile
only when the water is deep enough to cover its body. No effective biocontrol
agent has been found so far. The chemical molluscicides are the major control
tools for apple snail control. |
| Economic damage |
| Apple snails feed on a wide range of aquatic plants such as rice,
lotus, water spinach, water bamboo, lotuses, water caltrops etc. They prefer
young and soft plant parts such as rice seedlings, water spinach and the
young shoots of water caltrops. Scraping rice plants along water surface
by the snails causes delayed maturity, and reduction of tillers and panicles.
In average, a matured apple snail with shell height 3.5 cm can consume
about 12 rice seedlings per day. High population of apple snails can cause
more than 50% of yield loss in rice fields. The annual control cost could
reach up to about 5 million US dollars.Apple snails feed on a wide range
of plants such as rice (Oryza sativa), water spinach (Ipomoea reptans), water bamboo (Zizania latifolia Turcz.)(Z.aquatica L.), water caltrop (Trapa bicornis), taro (Colocasta esculenta (L.) Schott), water hyacinth (Eichhornia crassipes), duckweed (family Lemnaceae), algae, moss etc. |
| Reproduction |
| Apple snail reproduces rapidly. It occurs two generations per year
in central Taiwan. In some occasion, the generations can reach up to four
per year. Apple snails at different growth stages can be found all year
round, and their incubation period and hatchability can be very depending
on temperature. At the temperature range between 24 and 32 C, the incubation
period will be 10 to 20 days while the hatchability of the eggs can reach
66.7% to 81.3%. The hatchability decreases at the temperature lower than
20 C or above 30 C. Under favorable conditions, the apple snail takes 70
to 80 days to reach sexual maturity. The females start ovipositioning within
2 to 6 days after copulation. The size of egg masses is related to the
size of the snail, and the average egg number per egg mass can range from
200 to 300. In average, one female lays 6.8 egg masses per season and totally
7,000 to 9,000 eggs per year. |
| Growth |
| Apple snails take 88 days in summer and 204 days in winter to complete
one generation. They lay egg masses at dusk to dawn on any vegetation,
levees, and objects (e.g. twigs, stakes, stones, etc.) above the water
surface. Egg masses are bright pinkish-red and turn light pink when about
to hatch in 10 to 14 days. Hatchlings grow and mature fast. They are voracious
feeders. The optimal temperature of the snail is 25 to 27 C. During the
dry season, or in the water at the temperature lower than 20 C or higher
than 30 C, apple snails tightly close their operculums and bury themselves
in moist soil. They can aestivate for 6 months without intense sun irradiation,
then become active again when the soil is flooded. The longevity of apple
snails in the field is over 3 years. |
| Countermeasure |
| 1. Chmical control: The economical threshold for chemical application
is when snail number reaches one big snail or two middle snails or five
small snails per square meter of paddy field. The chemicals used are 70%
Niclosamide (0.4 kg/ha) or 80% Metaldehyde (1.2 kg/ha) in the paddy field
one to three days before transplanting of rice seedlings. The water level
should be maintained at 1 to 3 cm for 7 days. 2. Cultural control: (1)
After transplanting, maintain low water level (2 to 3 cm) in the paddy
field. Place a wire screen (meshes less than 5 mm) on the irrigation water
inlet to prevent the entry of snails. Put a 30 cm plastic wavy slab on
the water outlet to hinder the snails from flowing upstream. (2) In direct
seeding system, drain the field for 2 to 3 weeks soon after the sprouting
of the rice seeds in order to prevent the young seedlings from the snails
scraping. (3) Handpick and quash apple snails and their egg masses. 3.
Biological control: Release predators such as black carp fish or carp fish
in the pond and reservoir to prey on the snails. |
| Writer's name and affiliation |
| © Written by Kao, Ching-Wen. Bureau of Animal and Plant Health Inspection
and Quarantine, Council of Agriculture. (written in Nov. 2003) |
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