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Effective autodissemination of pyriproxyfen to breeding sites by the exophilic malaria vector Anopheles arabiensis in semi-field settings in Tanzania.

Lwetoijera D, Harris C, Kiware S, Dongus S, Devine GJ, McCall PJ, Majambere S - Malar. J. (2014)

Bottom Line: Laboratory bioassay of water samples from artificial habitats in these experiments resulted in significantly lower emergence rates in treated chambers (0.16 ± 0.23) compared to controls 0.97 ± 0.05) (p < 0.0001).In experiments where no mosquitoes introduced, there were no significant differences between control and treatment, indicating that transfer of PPF to breeding sites only occurred when mosquitoes were present; i.e. that autodissemination had occurred.Treatment of a single clay pot reduced adult emergence in six habitats to (0.34 ± 0.13) compared to (0.98 ± 0.02) in the controls (p < 0.0001), showing a high level of habitats coverage amplification of the autodissemination event.

View Article: PubMed Central - HTML - PubMed

Affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, P,O, Box 53, Ifakara, Tanzania. dwilson@ihi.or.tz.

ABSTRACT

Background: Malaria vector control strategies that target adult female mosquitoes are challenged by the emergence of insecticide resistance and behavioural resilience. Conventional larviciding is restricted by high operational costs and inadequate knowledge of mosquito-breeding habitats in rural settings that might be overcome by the juvenile hormone analogue, Pyriproxyfen (PPF). This study assessed the potential for Anopheles arabiensis to pick up and transfer lethal doses of PPF from contamination sites to their breeding habitats (i.e. autodissemination of PPF).

Methods: A semi-field system (SFS) with four identical separate chambers was used to evaluate PPF-treated clay pots for delivering PPF to resting adult female mosquitoes for subsequent autodissemination to artificial breeding habitats within the chambers. In each chamber, a tethered cow provided blood meals to laboratory-reared, unfed female An. arabiensis released in the SFS. In PPF-treated chambers, clay pot linings were dusted with 0.2 - 0.3 g AI PPF per pot. Pupae were removed from the artificial habitats daily, and emergence rates calculated. Impact of PPF on emergence was determined by comparing treatment with an appropriate control group.

Results: Mean (95% CI) adult emergence rates were (0.21 ± 0.299) and (0.95 ± 0.39) from PPF-treated and controls respectively (p < 0.0001). Laboratory bioassay of water samples from artificial habitats in these experiments resulted in significantly lower emergence rates in treated chambers (0.16 ± 0.23) compared to controls 0.97 ± 0.05) (p < 0.0001). In experiments where no mosquitoes introduced, there were no significant differences between control and treatment, indicating that transfer of PPF to breeding sites only occurred when mosquitoes were present; i.e. that autodissemination had occurred. Treatment of a single clay pot reduced adult emergence in six habitats to (0.34 ± 0.13) compared to (0.98 ± 0.02) in the controls (p < 0.0001), showing a high level of habitats coverage amplification of the autodissemination event.

Conclusion: The study provides proof of principle for the autodissemination of PPF to breeding habitats by malaria vectors. These findings highlight the potential for this technique for outdoor control of malaria vectors and call for the testing of this technique in field trials.

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Number of pupae produced (A), adults emerged (B), proportion of adult emerged (C) in the breeding habitats and proportion of adult emerged from larval bioassay on water samples from control and PPF - treated sections (D).
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Figure 2: Number of pupae produced (A), adults emerged (B), proportion of adult emerged (C) in the breeding habitats and proportion of adult emerged from larval bioassay on water samples from control and PPF - treated sections (D).

Mentions: The results of the experiments measuring the impact of PPF-treated resting pots on emergence from nearby breeding habitats are summarized in Figure 2. In the six replicates carried out, an average proportion (95% CI) of adult emerged per experimental replicate was 0.95 ± 0.39) in the control group compared to 0.21 ± 2.99) in the PPF treatments (p < 0.0001) (Figure 2C). There was no difference in the mean number (95% CI) of pupae collected from the treatment group (717 ± 622.8) compared with the control group (590 ± 220.9) (p = 0.579) (Figure 2A), suggesting that oviposition behaviour of mosquitoes after PPF treatment was not affected by the treatment. However, mean (95% CI) proportion of adult emerged from collected pupae were significantly high in the control group (558 ± 201.9) compared with the treatment group (130.5 ± 155.6) (p < 0.0001) (Figure 2B). Low adult emergence rate observed in the treatment chambers strongly suggest the occurrence of PPF autodissemination events mediated by gravid female mosquitoes attempting to oviposit.


Effective autodissemination of pyriproxyfen to breeding sites by the exophilic malaria vector Anopheles arabiensis in semi-field settings in Tanzania.

Lwetoijera D, Harris C, Kiware S, Dongus S, Devine GJ, McCall PJ, Majambere S - Malar. J. (2014)

Number of pupae produced (A), adults emerged (B), proportion of adult emerged (C) in the breeding habitats and proportion of adult emerged from larval bioassay on water samples from control and PPF - treated sections (D).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4012545&req=5

Figure 2: Number of pupae produced (A), adults emerged (B), proportion of adult emerged (C) in the breeding habitats and proportion of adult emerged from larval bioassay on water samples from control and PPF - treated sections (D).
Mentions: The results of the experiments measuring the impact of PPF-treated resting pots on emergence from nearby breeding habitats are summarized in Figure 2. In the six replicates carried out, an average proportion (95% CI) of adult emerged per experimental replicate was 0.95 ± 0.39) in the control group compared to 0.21 ± 2.99) in the PPF treatments (p < 0.0001) (Figure 2C). There was no difference in the mean number (95% CI) of pupae collected from the treatment group (717 ± 622.8) compared with the control group (590 ± 220.9) (p = 0.579) (Figure 2A), suggesting that oviposition behaviour of mosquitoes after PPF treatment was not affected by the treatment. However, mean (95% CI) proportion of adult emerged from collected pupae were significantly high in the control group (558 ± 201.9) compared with the treatment group (130.5 ± 155.6) (p < 0.0001) (Figure 2B). Low adult emergence rate observed in the treatment chambers strongly suggest the occurrence of PPF autodissemination events mediated by gravid female mosquitoes attempting to oviposit.

Bottom Line: Laboratory bioassay of water samples from artificial habitats in these experiments resulted in significantly lower emergence rates in treated chambers (0.16 ± 0.23) compared to controls 0.97 ± 0.05) (p < 0.0001).In experiments where no mosquitoes introduced, there were no significant differences between control and treatment, indicating that transfer of PPF to breeding sites only occurred when mosquitoes were present; i.e. that autodissemination had occurred.Treatment of a single clay pot reduced adult emergence in six habitats to (0.34 ± 0.13) compared to (0.98 ± 0.02) in the controls (p < 0.0001), showing a high level of habitats coverage amplification of the autodissemination event.

View Article: PubMed Central - HTML - PubMed

Affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, P,O, Box 53, Ifakara, Tanzania. dwilson@ihi.or.tz.

ABSTRACT

Background: Malaria vector control strategies that target adult female mosquitoes are challenged by the emergence of insecticide resistance and behavioural resilience. Conventional larviciding is restricted by high operational costs and inadequate knowledge of mosquito-breeding habitats in rural settings that might be overcome by the juvenile hormone analogue, Pyriproxyfen (PPF). This study assessed the potential for Anopheles arabiensis to pick up and transfer lethal doses of PPF from contamination sites to their breeding habitats (i.e. autodissemination of PPF).

Methods: A semi-field system (SFS) with four identical separate chambers was used to evaluate PPF-treated clay pots for delivering PPF to resting adult female mosquitoes for subsequent autodissemination to artificial breeding habitats within the chambers. In each chamber, a tethered cow provided blood meals to laboratory-reared, unfed female An. arabiensis released in the SFS. In PPF-treated chambers, clay pot linings were dusted with 0.2 - 0.3 g AI PPF per pot. Pupae were removed from the artificial habitats daily, and emergence rates calculated. Impact of PPF on emergence was determined by comparing treatment with an appropriate control group.

Results: Mean (95% CI) adult emergence rates were (0.21 ± 0.299) and (0.95 ± 0.39) from PPF-treated and controls respectively (p < 0.0001). Laboratory bioassay of water samples from artificial habitats in these experiments resulted in significantly lower emergence rates in treated chambers (0.16 ± 0.23) compared to controls 0.97 ± 0.05) (p < 0.0001). In experiments where no mosquitoes introduced, there were no significant differences between control and treatment, indicating that transfer of PPF to breeding sites only occurred when mosquitoes were present; i.e. that autodissemination had occurred. Treatment of a single clay pot reduced adult emergence in six habitats to (0.34 ± 0.13) compared to (0.98 ± 0.02) in the controls (p < 0.0001), showing a high level of habitats coverage amplification of the autodissemination event.

Conclusion: The study provides proof of principle for the autodissemination of PPF to breeding habitats by malaria vectors. These findings highlight the potential for this technique for outdoor control of malaria vectors and call for the testing of this technique in field trials.

Show MeSH
Related in: MedlinePlus