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Egg mass of golden apple snail (IRRI)
Golden apple snail, golden miracle snail, Argentine apple snail, channelled apple snail, apple snail, golden "kuhol", Miami golden snail
Pomacea canaliculata (Lamarck)
The presence of the egg mass and the organism, and the symptoms such as the missing seedlings confirm the damage caused by the snail.
The damage symptoms are comparable to the symptoms caused by the rice caseworm. Although the latter have the leaves rolled into tubes or cases.
The golden apple snail is prevalent in wetland such as seasonal swamps or rice fields. It can also be found in irrigation canals and rivers. It has both gills and a lung-breathing organ. It digs deep into the mud and surfaces again after renewed flooding. During drought, it closes its operculum. Mating occurs any time of the day in all seasons of the year in places where there is a continuous supply of water.
The wide host range of the golden apple snail supports its continuous development. The presence of young seedlings and continuous flooding of the rice fields also encourage its population buildup. Water currents in rivers, irrigation systems and floods also contribute to its spread.
Its ability to aestivate during the dry season enhances its survival under adverse conditions.
The golden apple snail has a muddy brown shell. The shell is lighter than the darker and smaller native snails. Its succulent flesh is creamy white to golden pinkish or orange-yellow. The male has a convex operculum that curves out or away from the shell, whereas the female lid curves into the shell.
Neonates or the newly hatched snails have soft shell. The juveniles or young snails are <1.5 to 1.6 cm. Medium-sized snails have a shell height of 2 to 3 cm.
The eggs are bright pink or strawberry pink. With age, they lighten in color or turn light pink when about to hatch.
Further information about this species can be obtained at http://www.applesnail.net.
Aside from the rice plant, the golden apple snail also feeds and develops on azolla, duckweed, lotus, maize, parsley, pearl barley, ramie, rice, rush, taro, water chestnuts, water hyacinth, water oats, most lowland weeds, and other succulent leafy plants.
The golden apple snails rasp plant tissue and cut of stems with their file-like radula or horny tongue.
It is a serious pest of young rice seedlings because it often cuts and kills growing seedlings. It also leaves large patches without rice, is particularly a more serious problem in direct-seeded crops.
The golden apple snail is considered a major problem in direct-seeded rice.
During dry periods or drought, the golden apple snails remain inactive in rice fields. They become active when fields are flooded. In the Philippines, 400,000 ha of rice were reported to be infested in 1988. In 1989, more than 16,000 ha suffered from golden apple snail damage in Japan.
The golden apple snail is now considered of quarantine importance in many countries, eg., Australia, Malaysia, and United States.
There are physical, mechanical, cultural, biological, and chemical control measures recommended against the golden apple snail.
The physical control practice is to install screens with 5 mm mesh at water inlets. This can minimize the entry of snails into the rice fields and will also facilitate hand-collection.
Increase mortality by mechanical action prior to crop establishment is advisable. Other mechanical control measures include handpicking and crushing, staking with bamboo or other wooden stakes before and after transplanting can be practiced to facilitate egg mass collection. Likewise, the use of a hand-operated device to smash egg clusters between two snail egg clappers can also reduce the snail population.
Among the recommended cultural control measures, planting older seedlings, planting at higher densities, or planting on ridges above the water line are advised against the golden apple snail. The field can be leveled-off or hydrotiller or rototiller to prepare the land. An off-season tillage to crush snails can also be employed. Snails can also be exposed to sun. Draining the field is also advised. Crop rotation with a dryland crop and fallow periods is also recommended as control.
For easier drainage and collection of the golden apple snail, canalets can be constructed along bunds and inside paddies. Atractants like newspaper can be used.
Depressed strips can be constructed to retain a small amount of water drainage. This method also confines the snail to limited areas, hence handpicking can be facilitated. It can be done during the final harrowing period.
Good water management obtained by good levelling for the first two weeks is recommended.
The use of common carp, Japanese crucian, heron, and weasels as biological control agents against the golden apple snail were effective in Japan. A firefly nymph is also an effective natural enemy of the snail. Herding ducks and raising fish in the paddy are also recommended as biological control. Birds prey on both eggs and neonates. Rats and snakes also feed on them.
Molluscicides such as metaldehyde is recommended.
JLA Catindig and KL Heong