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Efficacy of ULV and thermal aerosols of deltamethrin for control of Aedes albopictus in nice, France

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ABSTRACT

Background: Ultra-low volume (ULV) insecticidal aerosols dispensed from vehicle-mounted cold-foggers are widely considered the method of choice for control of Aedes aegypti and Ae. albopictus during outbreaks of dengue and chikungunya and, more recently, Zika. Nevertheless, their effectiveness has been poorly studied, particularly in Europe. Nearly all published studies of ULV efficacy are bio-assays based on the mortality of caged mosquitoes. In our study we preferred to monitor the direct impact of treatments on the wild mosquito populations. This study was undertaken to evaluate the efficiency of the two widely used space spraying methods to control Ae. albopictus and Ae. aegypti.

Methods: We determined the susceptibility of local Ae. albopictus to deltamethrin by two methods: topical application and the “WHO Tube Test”. We used ovitraps baited with hay infusion and adult traps (B-G Sentinel) baited with a patented attractant to monitor the mosquitoes in four residential areas in Nice, southern France. The impact of deltamethrin applied from vehicle-mounted ULV fogging-machines was assessed by comparing trap results in treated vs untreated areas for 5 days before and 5 days after treatment. Four trials were conducted at the maximum permitted application rate (1 g.ha-1). We also made two small-scale tests of the impact of the same insecticide dispensed from a hand-held thermal fogger.

Results: Susceptibility to the insecticide was high but there was no discernable change in the oviposition rate or the catch of adult female mosquitoes, nor was there any change in the parous rate. In contrast, hand-held thermal foggers were highly effective, with more than 90% reduction of both laid eggs and females.

Conclusions: We believe that direct monitoring of the wild mosquito populations gives a realistic assessment of the impact of treatments and suggest that the lack of efficacy is due to lack of interaction between the target mosquitoes and the ULV aerosol. We discuss the factors that influence the effectiveness of both methods of spraying in the context of epidemic situations.

Electronic supplementary material: The online version of this article (doi:10.1186/s13071-016-1881-y) contains supplementary material, which is available to authorized users.

No MeSH data available.


Results of the GLM binomial analysis of the influence of ULV treatment (a–d) and thermal fogging treatment (e, f) on the daily number of captures of wild females and eggs
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Fig6: Results of the GLM binomial analysis of the influence of ULV treatment (a–d) and thermal fogging treatment (e, f) on the daily number of captures of wild females and eggs

Mentions: The local strain of Ae. albopictus was fully susceptible to deltamethrin by both methods (Table 2); values for KdT50 and KdT95 were similar (overlapping 95% CIs) to those of the Ae. aegypti reference strain. We investigated the effect of the insecticidal treatment on the density and parity rates of natural populations of Ae. albopictus. Weather conditions appeared optimum; wind-speed was < 10 km/h and thermal conditions were stable. There was no marked impact of the fogging treatments on oviposition rate, adult capture rate or parous rate in any of the four field ULV applications (Additional file 6: Table S2; Additional file 7: Table S3; Additional file 8: Table S4; Fig. 5). Our efforts to improve the cold fogging spraying method in residential habitat was not successful despite the change to a site with a more extensive road network (Fig. 2) which assumed better coverage of the targeted zone by the swath of the insecticide cloud. Furthermore, even when two applications were made three days apart there was no impact on the wild mosquito population as shown by GLM analysis (Fig. 6) and the variable interaction “Treatment*Pre/Post” is positive and significant or not significant for all of the cases (Additional file 5: Table S1). Hence, in general Cold Fogging was not effective on diminishing the abundance of eggs and females and females’ parity rates (Additional file 6: Table S2; Additional file 7: Table S3; Additional file 8: Table S4).Table 2


Efficacy of ULV and thermal aerosols of deltamethrin for control of Aedes albopictus in nice, France
Results of the GLM binomial analysis of the influence of ULV treatment (a–d) and thermal fogging treatment (e, f) on the daily number of captures of wild females and eggs
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5120493&req=5

Fig6: Results of the GLM binomial analysis of the influence of ULV treatment (a–d) and thermal fogging treatment (e, f) on the daily number of captures of wild females and eggs
Mentions: The local strain of Ae. albopictus was fully susceptible to deltamethrin by both methods (Table 2); values for KdT50 and KdT95 were similar (overlapping 95% CIs) to those of the Ae. aegypti reference strain. We investigated the effect of the insecticidal treatment on the density and parity rates of natural populations of Ae. albopictus. Weather conditions appeared optimum; wind-speed was < 10 km/h and thermal conditions were stable. There was no marked impact of the fogging treatments on oviposition rate, adult capture rate or parous rate in any of the four field ULV applications (Additional file 6: Table S2; Additional file 7: Table S3; Additional file 8: Table S4; Fig. 5). Our efforts to improve the cold fogging spraying method in residential habitat was not successful despite the change to a site with a more extensive road network (Fig. 2) which assumed better coverage of the targeted zone by the swath of the insecticide cloud. Furthermore, even when two applications were made three days apart there was no impact on the wild mosquito population as shown by GLM analysis (Fig. 6) and the variable interaction “Treatment*Pre/Post” is positive and significant or not significant for all of the cases (Additional file 5: Table S1). Hence, in general Cold Fogging was not effective on diminishing the abundance of eggs and females and females’ parity rates (Additional file 6: Table S2; Additional file 7: Table S3; Additional file 8: Table S4).Table 2

View Article: PubMed Central - PubMed

ABSTRACT

Background: Ultra-low volume (ULV) insecticidal aerosols dispensed from vehicle-mounted cold-foggers are widely considered the method of choice for control of Aedes aegypti and Ae. albopictus during outbreaks of dengue and chikungunya and, more recently, Zika. Nevertheless, their effectiveness has been poorly studied, particularly in Europe. Nearly all published studies of ULV efficacy are bio-assays based on the mortality of caged mosquitoes. In our study we preferred to monitor the direct impact of treatments on the wild mosquito populations. This study was undertaken to evaluate the efficiency of the two widely used space spraying methods to control Ae. albopictus and Ae. aegypti.

Methods: We determined the susceptibility of local Ae. albopictus to deltamethrin by two methods: topical application and the &ldquo;WHO Tube Test&rdquo;. We used ovitraps baited with hay infusion and adult traps (B-G Sentinel) baited with a patented attractant to monitor the mosquitoes in four residential areas in Nice, southern France. The impact of deltamethrin applied from vehicle-mounted ULV fogging-machines was assessed by comparing trap results in treated vs untreated areas for 5&nbsp;days before and 5&nbsp;days after treatment. Four trials were conducted at the maximum permitted application rate (1&nbsp;g.ha-1). We also made two small-scale tests of the impact of the same insecticide dispensed from a hand-held thermal fogger.

Results: Susceptibility to the insecticide was high but there was no discernable change in the oviposition rate or the catch of adult female mosquitoes, nor was there any change in the parous rate. In contrast, hand-held thermal foggers were highly effective, with more than 90% reduction of both laid eggs and females.

Conclusions: We believe that direct monitoring of the wild mosquito populations gives a realistic assessment of the impact of treatments and suggest that the lack of efficacy is due to lack of interaction between the target mosquitoes and the ULV aerosol. We discuss the factors that influence the effectiveness of both methods of spraying in the context of epidemic situations.

Electronic supplementary material: The online version of this article (doi:10.1186/s13071-016-1881-y) contains supplementary material, which is available to authorized users.

No MeSH data available.