Limits...
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.

Show MeSH

Related in: MedlinePlus

Average proportion (± s.e.) of larvae of An. gambiae s.s. surviving on damp soil after exposure to different periods of drought. The lines show the models after back-transformation of the linear model (arcsine(√ p) = a * time + b) obtained after arcsine square root transformation of the original data. Model descriptions are given in Table 2. A: first-instar larvae, B: second-instar larvae.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC183857&req=5

Figure 3: Average proportion (± s.e.) of larvae of An. gambiae s.s. surviving on damp soil after exposure to different periods of drought. The lines show the models after back-transformation of the linear model (arcsine(√ p) = a * time + b) obtained after arcsine square root transformation of the original data. Model descriptions are given in Table 2. A: first-instar larvae, B: second-instar larvae.

Mentions: Figures 3 and 4 show the average proportion of larvae that appeared at the water surface, and thus survived, after exposure to different periods of drought for all four larval stages. The estimated regression parameters of the linear models that were fitted through the data after arcsine square root transformation are shown in Table 2. By comparing the 95% confidence intervals of regression coefficient a of the fourth-instar with that of the other three instars, we found that survival of fourth-instar larvae was significantly higher than of the other three instars (P < 0.05). Using the model, we predicted that 50% of first, second and third-instar larvae had died after 31, 29 and 33 hours, respectively, while 50% of the fourth-instar larvae had died after 53 hours (Table 2). We estimated that first, second and third-instar larvae could survive up to 64, 65 and 69 hours, respectively, while fourth-instar larvae survive up to 113 hours (4.7 days) under the experimental conditions.


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)

Average proportion (± s.e.) of larvae of An. gambiae s.s. surviving on damp soil after exposure to different periods of drought. The lines show the models after back-transformation of the linear model (arcsine(√ p) = a * time + b) obtained after arcsine square root transformation of the original data. Model descriptions are given in Table 2. A: first-instar larvae, B: second-instar larvae.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 3: Average proportion (± s.e.) of larvae of An. gambiae s.s. surviving on damp soil after exposure to different periods of drought. The lines show the models after back-transformation of the linear model (arcsine(√ p) = a * time + b) obtained after arcsine square root transformation of the original data. Model descriptions are given in Table 2. A: first-instar larvae, B: second-instar larvae.
Mentions: Figures 3 and 4 show the average proportion of larvae that appeared at the water surface, and thus survived, after exposure to different periods of drought for all four larval stages. The estimated regression parameters of the linear models that were fitted through the data after arcsine square root transformation are shown in Table 2. By comparing the 95% confidence intervals of regression coefficient a of the fourth-instar with that of the other three instars, we found that survival of fourth-instar larvae was significantly higher than of the other three instars (P < 0.05). Using the model, we predicted that 50% of first, second and third-instar larvae had died after 31, 29 and 33 hours, respectively, while 50% of the fourth-instar larvae had died after 53 hours (Table 2). We estimated that first, second and third-instar larvae could survive up to 64, 65 and 69 hours, respectively, while fourth-instar larvae survive up to 113 hours (4.7 days) under the experimental conditions.

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