PRESENT SITUATION OF POMACEA CANALICULATA IN ARGENTINA

Nestor J. Cazzaniga

Universidad Nacional del Sur
Departamento de Biología
Bioquímica y Farmacia. San Juan 670
(8000) Bahía Blanca, Argentina
E-mail: ficazzan@criba.edu.ar

Pomacea canaliculata is autochthonous in Argentina. It inhabits lakes, swamps and rivers over about one million square kilometres, including the rice producing area in Northeast Argentina. Natural limits are mainly drawn by aridness and height (Cazzaniga, 1987); apple snails fail to thrive in salty, alkaline, poorly vegetated environment with high risk of desiccation. They generally live in shallow, quiet, turbid sites, with low Na+/(K+ + Mg++) ratios (Martin et al., 2001).

Apple snails are considered as harmless and useless in Argentina. Even though they are abundant in rice fields, only one non-tillage paddy field was recorded as damaged by apple snails in Chaco province (T. Wada and E. Albrecht, pers. comm., 1998). No other cases of damage have been detected during the last past four years, according to the records of the National Institute of Farming Technology (INTA) (Alfredo Marin, INTA Corrientes, pers. comm. September 2002).

Rice is not a main crop in Argentina. Out of the 13.3 million hectares seeded with cereals in summer 2000/2001, rice occupied the seventh place, with 154,035 ha (1,16 %) (Table 1). The evolution of the seeded area in Argentina during the period 1990/2001 is shown in Figure 1; after a peak of 290,000 ha in 1998/99, the rice producing area declined because of commercial difficulties.

Table 1. Cereal seeded area in Argentina during the 2000/2001 campaign.

(Source: Ministerio de Economía de la Nación, Secretaría de Agricultura, Ganadería y Pesca, Argentina.)

Figure 1. Area seeded with rice in Argentina during the period 1990-2000. (Source: Ministerio de Economía de la Nación, Secretaría de Agricultura, Ganadería y Pesca, Argentina).

The 2000/2001 production was 859,140 ton, with a mean yield of 5698.35 kg/ha. Since Argentine people have the lowest per capita consumption of rice in South America (only 6-kg/person year), more than 75 % of the production is exported, mainly to Brazil.

The reasons why P. canaliculata is not a pest in Argentina were not fully elucidated. Certainly, a set of autochthonous predators and competitors are perhaps regulating apple snail populations, but snails are still very abundant in the natural environments around rice fields and within the paddies themselves. Individual rice fields are very large in Argentina, a single owner seeding as much as 1 000 to 4 000 ha, using heavy machinery on dry soil. Ploughing work probably kills most buried apple snails. Rice is seeded from the end of Winter (late August) to middle Spring (November) depending on the zone, i.e., when the main rainy season begins (Figure 2). Then, rice plants emerge under the effects of rain and, when the field is flooded through irrigation channels or underwater pumping, apple snails invade the paddy quite late. The timing of this process has not been assessed, but it is probable that, by the time apple snails enter the field, rice plants are strong enough to resist their attack, and snails probably feed mostly on aquatic weeds.

Figure 2. Monthly mean temperature (curve) and rain (bars) of the province of Corrientes, in the rice producing area of Argentina.

It seems significant that the only farmer that asked for advise on apple snail control is used to seeding rice under a non-tillage scheme, so that he does not take advantage of the snail reducing effect of plough work. This farmer controlled the problem mainly by spreading copper sulphate on the field. The use of this chemical is legal in Argentina, where it is also used as fungicide on seeds, and to control algae in swimming pools.

Apple snails are used neither as human food, nor for other purposes in Argentina.

A project of integrated management of aquatic weeds was conducted in southern Buenos Aires province by the end of the 1970s. The problem was soil salination caused by weed plugging of the drainage channels in an irrigation area under a semiarid climate. Different strategies were proposed, one of which was transplanting P. canaliculata from its southernmost limit (some 200 km to the North of the problem area) to enclosures within the channels. The following conditions were evaluated before this action was carried out: 1) the channels were artificial habitats, with fauna and flora lacking a special interest from a conservationist viewpoint (Cazzaniga, 1981a); 2) the channels fill up through the bottom with underground water, and they are not directly connected to any other water body, so that apple snails could not easily escape to natural habitats; 3) in this semiarid region there was no possibility of producing rice or any other aquatic crop that could be attacked by the snails; 4) there are not human- or cattle-transmissible parasites hosted by P. canaliculata (e.g., Angiostrongylus spp.) in Argentina; 5) the snails were retained within enclosures for small tests before their release to the field. Enclosure trials were successful (Cazzaniga, 1981b), the snails showed reproductive activity in the channels and some local farmers began to collect snails from the enclosures to spread them for weeding in their water tanks.

Carps (Cyprinus carpio L.) were later introduced to the channels, with no official control. After bottom disturbance by the carps and the increment of water turbidity in the channels, a weeding programme with apple snails was no longer of interest.

At present, there are not research programmes on applied ecology of apple snails; only research on basic aspects is granted by Argentine official agencies.

Literature cited

Cazzaniga, N.J., 1981a. Caracterización química y faunística de canales de drenaje delValle Inferior del Río Colorado (Partidos de Villarino y Patagones, Provincia de Buenos Ai­res). Ecosur, 8 (15): 25-46.

Cazzaniga, N. J., 1981b. Evaluación preliminar de un gasterópodo para el control de malezas acuáticas sumergidas. En: CIC, II Reunión sobre Malezas Subacuáticas en Canales de De­sagüe de CORFO, pp. 131-165. La Plata.

Cazzaniga, N. J., 1983. Apple-snails eating Chara. Aquaphyte, 3 (2): 1,4. Gainesville, Florida.
Cazzaniga, N. J., 1987a. Pomacea canaliculata (Lamarck, 1801) en Catamarca y un co­men­tario sobre Ampullaria catamarcensis Sowerby, 1874 (Gastropoda Ampul­la­ri­i­dae). Iheringia, série Zoologia, 66: 43-68.

Cazzaniga, N. J., 1987b. Pomacea canaliculata (Gastropoda) en la Provincia de San Juan. Neotropica, 33 (89): 10.

Cazzaniga, N.J. & A.L. Estebenet, 1985. Revisión de antecedentes sobre el uso de cara­­coles (Ampullariidae) en programas de control biológico. Malezas, 13 (1): 23-39.

Estebenet, A. L. & N. J. Cazzaniga, 1990. Effect of short-term exposure to copper on survival of apple-snails in an integrated control program. Journal of Aquatic Plant Management, 28: 103-105.

Fernandez, O.A., J.H. Irigoyen, M.R. Sabbatini & R.E. Brevedan, 1987. Aquatic plant management in drainage canals of southern Argentina. Journal of Aquatic Plant Management 25: 65-67.

Fernandez, O.A., D.L. Sutton, V.H. Lallana, M.R. Sabbatini & J.H. Irigoyen, 1989. South and Central America. In: A.H. Pieterse & K.J. Murphy (eds.), Aquatic Weeds. The ecology and management of nuisance aquatic vegetation. Osford University Press, London.

Martin, P.R., A.L. Estebenet & N.J. Cazzaniga, 2001. Factors affecting the distribution of Pomacea canaliculata (Gastropoda: Ampullariidae) along its southernmost natural limit. Malacologia 43 (1-2): 13-23.

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