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Egg hatching, larval movement and larval survival of the malaria vector Anopheles gambiae in desiccating habitats.

Koenraadt CJ, Paaijmans KP, Githeko AK, Knols BG, Takken W - Malar. J. (2003)

Bottom Line: However, proportions of larvae reaching the site decreased rapidly with increasing distance.Fourth-instar larvae survived significantly longer and we estimated that the maximum survival time was 113 hrs.In addition, the results suggest that, for larval vector control methods to be effective, habitats should remain drained for at least 5 days to kill all larvae (e.g. in rice fields) and habitats that recently dried up should be treated as well, if larvicidal agents are applied.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Entomology, Department of Plant Sciences, Wageningen University, The Netherlands. sander.koenraadt@wur.nl

ABSTRACT

Background: Although the effects of rainfall on the population dynamics of the malaria vector Anopheles gambiae have been studied in great detail, the effects of dry periods on its survival remain less clear.

Methods: The effects of drying conditions were simulated by creating desiccated habitats, which consisted of trays filled with damp soil. Experiments were performed in these trays to (i) test the ability of An. gambiae sensu stricto eggs to hatch on damp soil and for larvae to reach an artificial breeding site at different distances of the site of hatching and (ii) to record survival of the four larval stages of An. gambiae s.s. when placed on damp soil.

Results: Eggs of An. gambiae s.s. hatched on damp soil and emerging larvae were capable of covering a distance of up to 10 cm to reach surface water enabling further development. However, proportions of larvae reaching the site decreased rapidly with increasing distance. First, second and third-instar larvae survived on damp soil for an estimated period of 64, 65 and 69 hrs, respectively. Fourth-instar larvae survived significantly longer and we estimated that the maximum survival time was 113 hrs.

Conclusion: Short-term survival of aquatic stages of An. gambiae on wet soil may be important and adaptive when considering the transient nature of breeding sites of this species in sub-Saharan Africa. In addition, the results suggest that, for larval vector control methods to be effective, habitats should remain drained for at least 5 days to kill all larvae (e.g. in rice fields) and habitats that recently dried up should be treated as well, if larvicidal agents are applied.

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Experimental set-up of the egg hatching experiment showing the positions of the filter paper relative to the simulated breeding site.
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Figure 1: Experimental set-up of the egg hatching experiment showing the positions of the filter paper relative to the simulated breeding site.

Mentions: Plastic plates (18 cm , 4 cm deep) or trays (40 × 30 × 11 cm) were filled to a depth of 4 cm with local, black cotton soil, which was first saturated with river water. The topsoil layer was smoothed and in the middle of the plates or trays, breeding sites were simulated by making circular depressions (5 cm , 2 – 3 cm deep), which were filled with river water. Fifty eggs of An. gambiae s.s., that had been incubated for one day on wet filter paper, were placed on a small piece of filter paper (0.5 × 1.0 cm). This filter paper was placed directly in the site with water (control) or on the damp soil at 0, 2, 5 or 10 cm from the edge of the artificial breeding site (Figure 1). Each distance experiment was replicated 5 times, each replicate (plate or tray) receiving one batch of 50 eggs. The control, 0 and 2 cm distance experiments were carried out in the plates, while the 5 and 10 cm distance experiments were done in the trays. Plates and trays were placed in a laboratory of the CVBCR, without controlled environmental conditions. During the experiment, mean minimum indoor temperature was 19°C and mean maximum indoor temperature 30°C. Plates and trays were not exposed to direct sunlight.


Egg hatching, larval movement and larval survival of the malaria vector Anopheles gambiae in desiccating habitats.

Koenraadt CJ, Paaijmans KP, Githeko AK, Knols BG, Takken W - Malar. J. (2003)

Experimental set-up of the egg hatching experiment showing the positions of the filter paper relative to the simulated breeding site.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC183857&req=5

Figure 1: Experimental set-up of the egg hatching experiment showing the positions of the filter paper relative to the simulated breeding site.
Mentions: Plastic plates (18 cm , 4 cm deep) or trays (40 × 30 × 11 cm) were filled to a depth of 4 cm with local, black cotton soil, which was first saturated with river water. The topsoil layer was smoothed and in the middle of the plates or trays, breeding sites were simulated by making circular depressions (5 cm , 2 – 3 cm deep), which were filled with river water. Fifty eggs of An. gambiae s.s., that had been incubated for one day on wet filter paper, were placed on a small piece of filter paper (0.5 × 1.0 cm). This filter paper was placed directly in the site with water (control) or on the damp soil at 0, 2, 5 or 10 cm from the edge of the artificial breeding site (Figure 1). Each distance experiment was replicated 5 times, each replicate (plate or tray) receiving one batch of 50 eggs. The control, 0 and 2 cm distance experiments were carried out in the plates, while the 5 and 10 cm distance experiments were done in the trays. Plates and trays were placed in a laboratory of the CVBCR, without controlled environmental conditions. During the experiment, mean minimum indoor temperature was 19°C and mean maximum indoor temperature 30°C. Plates and trays were not exposed to direct sunlight.

Bottom Line: However, proportions of larvae reaching the site decreased rapidly with increasing distance.Fourth-instar larvae survived significantly longer and we estimated that the maximum survival time was 113 hrs.In addition, the results suggest that, for larval vector control methods to be effective, habitats should remain drained for at least 5 days to kill all larvae (e.g. in rice fields) and habitats that recently dried up should be treated as well, if larvicidal agents are applied.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Entomology, Department of Plant Sciences, Wageningen University, The Netherlands. sander.koenraadt@wur.nl

ABSTRACT

Background: Although the effects of rainfall on the population dynamics of the malaria vector Anopheles gambiae have been studied in great detail, the effects of dry periods on its survival remain less clear.

Methods: The effects of drying conditions were simulated by creating desiccated habitats, which consisted of trays filled with damp soil. Experiments were performed in these trays to (i) test the ability of An. gambiae sensu stricto eggs to hatch on damp soil and for larvae to reach an artificial breeding site at different distances of the site of hatching and (ii) to record survival of the four larval stages of An. gambiae s.s. when placed on damp soil.

Results: Eggs of An. gambiae s.s. hatched on damp soil and emerging larvae were capable of covering a distance of up to 10 cm to reach surface water enabling further development. However, proportions of larvae reaching the site decreased rapidly with increasing distance. First, second and third-instar larvae survived on damp soil for an estimated period of 64, 65 and 69 hrs, respectively. Fourth-instar larvae survived significantly longer and we estimated that the maximum survival time was 113 hrs.

Conclusion: Short-term survival of aquatic stages of An. gambiae on wet soil may be important and adaptive when considering the transient nature of breeding sites of this species in sub-Saharan Africa. In addition, the results suggest that, for larval vector control methods to be effective, habitats should remain drained for at least 5 days to kill all larvae (e.g. in rice fields) and habitats that recently dried up should be treated as well, if larvicidal agents are applied.

Show MeSH
Related in: MedlinePlus