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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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Relationship between anopheline mosquitoes and diversity of other emergent insects.
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Figure 4: Relationship between anopheline mosquitoes and diversity of other emergent insects.

Mentions: Multivariate modelling demonstrated that adult An. gambiae s.l. were more common in rice fields 0–100 m from the landward edge of the floodplains, particularly along the field edges (Table 5). Emergence of anopheline adults was associated with shorter rice plants and the simultaneous emergence of culicine adults. Whilst there was a strong relationship between the abundance of An. gambiae s.l. adults and insect richness (Figure 4; r2 = 0.43, F = 62.2 P < 0.001), after adjuting for covariates the number of invertebrate taxa was of borderline statistical significance, suggesting that An. gambiae s.l. adult emergence was weakly associated with higher invertebrate diversity.


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)

Relationship between anopheline mosquitoes and diversity of other emergent insects.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Relationship between anopheline mosquitoes and diversity of other emergent insects.
Mentions: Multivariate modelling demonstrated that adult An. gambiae s.l. were more common in rice fields 0–100 m from the landward edge of the floodplains, particularly along the field edges (Table 5). Emergence of anopheline adults was associated with shorter rice plants and the simultaneous emergence of culicine adults. Whilst there was a strong relationship between the abundance of An. gambiae s.l. adults and insect richness (Figure 4; r2 = 0.43, F = 62.2 P < 0.001), after adjuting for covariates the number of invertebrate taxa was of borderline statistical significance, suggesting that An. gambiae s.l. adult emergence was weakly associated with higher invertebrate diversity.

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