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Agriculture and the promotion of insect pests: rice cultivation in river floodplains and malaria vectors in The Gambia.

Jarju LB, Fillinger U, Green C, Louca V, Majambere S, Lindsay SW - Malar. J. (2009)

Bottom Line: Semi-field studies demonstrated that cattle faeces nearly doubled the number of anopheline larvae compared with untreated water.A consequence of this cultivation is the provizion of ideal conditions for malaria vectors to thrive.As the demand for locally-produced rice grows, increased rice farming will generate great numbers of vectors; emphasizing the need to protect local communities against malaria.

View Article: PubMed Central - HTML - PubMed

Affiliation: National Malaria Control Programme, Banjul, the Gambia. lbsjarju@yahoo.ac.uk

ABSTRACT

Background: Anthropogenic modification of natural habitats can create conditions in which pest species associated with humans can thrive. In order to mitigate for these changes, it is necessary to determine which aspects of human management are associated with the promotion of those pests. Anopheles gambiae, the main Africa malaria vector, often breeds in rice fields. Here the impact of the ancient practice of 'swamp rice' cultivation, on the floodplains of the Gambia River, on the production of anopheline mosquitoes was investigated.

Methods: Routine surveys were carried out along 500 m transects crossing rice fields from the landward edge of the floodplains to the river during the 2006 rainy season. Aquatic invertebrates were sampled using area samplers and emergence traps and fish sampled using nets. Semi-field experiments were used to investigate whether nutrients used for swamp rice cultivation affected mosquito larval abundance.

Results: At the beginning of the rainy season rice is grown on the landward edge of the floodplain; the first area to flood with fresh water and one rich in cattle dung. Later, rice plants are transplanted close to the river, the last area to dry out on the floodplain. Nearly all larval and adult stages of malaria vectors were collected 0-100 m from the landward edge of the floodplains, where immature rice plants were grown. These paddies contained stagnant freshwater with high quantities of cattle faeces. Semi-field studies demonstrated that cattle faeces nearly doubled the number of anopheline larvae compared with untreated water.

Conclusion: Swamp rice cultivation creates ideal breeding sites for malaria vectors. However, only those close to the landward edge harboured vectors. These sites were productive since they were large areas of standing freshwater, rich in nutrients, protected from fish, and situated close to human habitation, where egg-laying mosquitoes from the villages had short distances to fly. The traditional practice of 'swamp rice' cultivation uses different bodies of water on the floodplains to cultivate rice during the rainy season. A consequence of this cultivation is the provizion of ideal conditions for malaria vectors to thrive. As the demand for locally-produced rice grows, increased rice farming will generate great numbers of vectors; emphasizing the need to protect local communities against malaria.

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Related in: MedlinePlus

Local rice production and imports in relation to the rizing population in The Gambia. No data on imported rice prior to 1990. Data from FAO  and Webb 1992 [21].
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Figure 6: Local rice production and imports in relation to the rizing population in The Gambia. No data on imported rice prior to 1990. Data from FAO and Webb 1992 [21].

Mentions: Whilst increased production of malaria mosquitoes is an inevitable consequence of rice production, swamp rice cultivation is likely to increase in the future. Rice is the staple food in The Gambia and locally produced rice has failed to keep up with the demand for more rice for the growing population, with imports soaring (Figure 6), straining the country's meagre financial resources. Since the world's consumption of rice outstrips production rice prices are expected to double in the next two years (: accessed 26/6/8). Thus local production of rice must increase, to offset the rapidly increasing cost of imports. Increasing acreages of rice will increase the vector population. Quite what this will mean for the level of malaria in the country is uncertain, since generally in sub-Saharan Africa increasing transmission associated with rice irrigation does not necessarily lead to more malaria [4]. Nevertheless, it is essential to ensure that local communities near rice-growing areas are protected from the potentially lethal infection. This study demonstrates that in this area, treating rice fields close to the landward edge of the floodplains with larvicides would help reduce transmission levels, yet this approach is unlikely to be entirely satisfactory since the extremely low productivity of sites further away will continue to generate appreciable numbers of vectors. In these circumstances attacking the vectors that enter houses with long-lasting impregnated nets, indoor residual spraying or both combined, together with prompt and effective treatment of clinical cases of malaria, should be advocated.


Agriculture and the promotion of insect pests: rice cultivation in river floodplains and malaria vectors in The Gambia.

Jarju LB, Fillinger U, Green C, Louca V, Majambere S, Lindsay SW - Malar. J. (2009)

Local rice production and imports in relation to the rizing population in The Gambia. No data on imported rice prior to 1990. Data from FAO  and Webb 1992 [21].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2734858&req=5

Figure 6: Local rice production and imports in relation to the rizing population in The Gambia. No data on imported rice prior to 1990. Data from FAO and Webb 1992 [21].
Mentions: Whilst increased production of malaria mosquitoes is an inevitable consequence of rice production, swamp rice cultivation is likely to increase in the future. Rice is the staple food in The Gambia and locally produced rice has failed to keep up with the demand for more rice for the growing population, with imports soaring (Figure 6), straining the country's meagre financial resources. Since the world's consumption of rice outstrips production rice prices are expected to double in the next two years (: accessed 26/6/8). Thus local production of rice must increase, to offset the rapidly increasing cost of imports. Increasing acreages of rice will increase the vector population. Quite what this will mean for the level of malaria in the country is uncertain, since generally in sub-Saharan Africa increasing transmission associated with rice irrigation does not necessarily lead to more malaria [4]. Nevertheless, it is essential to ensure that local communities near rice-growing areas are protected from the potentially lethal infection. This study demonstrates that in this area, treating rice fields close to the landward edge of the floodplains with larvicides would help reduce transmission levels, yet this approach is unlikely to be entirely satisfactory since the extremely low productivity of sites further away will continue to generate appreciable numbers of vectors. In these circumstances attacking the vectors that enter houses with long-lasting impregnated nets, indoor residual spraying or both combined, together with prompt and effective treatment of clinical cases of malaria, should be advocated.

Bottom Line: Semi-field studies demonstrated that cattle faeces nearly doubled the number of anopheline larvae compared with untreated water.A consequence of this cultivation is the provizion of ideal conditions for malaria vectors to thrive.As the demand for locally-produced rice grows, increased rice farming will generate great numbers of vectors; emphasizing the need to protect local communities against malaria.

View Article: PubMed Central - HTML - PubMed

Affiliation: National Malaria Control Programme, Banjul, the Gambia. lbsjarju@yahoo.ac.uk

ABSTRACT

Background: Anthropogenic modification of natural habitats can create conditions in which pest species associated with humans can thrive. In order to mitigate for these changes, it is necessary to determine which aspects of human management are associated with the promotion of those pests. Anopheles gambiae, the main Africa malaria vector, often breeds in rice fields. Here the impact of the ancient practice of 'swamp rice' cultivation, on the floodplains of the Gambia River, on the production of anopheline mosquitoes was investigated.

Methods: Routine surveys were carried out along 500 m transects crossing rice fields from the landward edge of the floodplains to the river during the 2006 rainy season. Aquatic invertebrates were sampled using area samplers and emergence traps and fish sampled using nets. Semi-field experiments were used to investigate whether nutrients used for swamp rice cultivation affected mosquito larval abundance.

Results: At the beginning of the rainy season rice is grown on the landward edge of the floodplain; the first area to flood with fresh water and one rich in cattle dung. Later, rice plants are transplanted close to the river, the last area to dry out on the floodplain. Nearly all larval and adult stages of malaria vectors were collected 0-100 m from the landward edge of the floodplains, where immature rice plants were grown. These paddies contained stagnant freshwater with high quantities of cattle faeces. Semi-field studies demonstrated that cattle faeces nearly doubled the number of anopheline larvae compared with untreated water.

Conclusion: Swamp rice cultivation creates ideal breeding sites for malaria vectors. However, only those close to the landward edge harboured vectors. These sites were productive since they were large areas of standing freshwater, rich in nutrients, protected from fish, and situated close to human habitation, where egg-laying mosquitoes from the villages had short distances to fly. The traditional practice of 'swamp rice' cultivation uses different bodies of water on the floodplains to cultivate rice during the rainy season. A consequence of this cultivation is the provizion of ideal conditions for malaria vectors to thrive. As the demand for locally-produced rice grows, increased rice farming will generate great numbers of vectors; emphasizing the need to protect local communities against malaria.

Show MeSH
Related in: MedlinePlus