To block the local transmission of Zika virus (ZIKV) in Volusia County, its primary vector mosquitoes Aedes aegypti and Ae. albopictus, at larval stage, were controlled by spraying very-fine to fine (VF/F) droplets of VectoBac WDG (Bacillus thuringiensis israelensis) at the rate of 0.56 kg/ha in four areas using a helicopter low-volume (LV) system. The spray effects were verified using droplet-collecting cards and cups set in the fields. Cup bioassay on Ae. aegypti larvae was conducted to estimate the mortalities. The droplet sizes and densities ranged between 80-364 µm and 16-29 droplets / cm2, respectively. The overall mortality reached 93 ± 15% (χ~ ± SD) at 24 hours and 95 ± 13% at 48 hours, and no significant mortality difference was detected among the coverage treatments, between the yard and forest settings, and among the spray areas. The results indicate expected larval control effects. The effectiveness influenced by weather, humidity and forest were discussed, and the relevant improvements were recommended.
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