Mr. Mister: Rockin' the Aedes of the San Francisco Bay Salt Marshes

Mist sprayers (MS) are being rapidly adopted nationwide for applying larvicides to control peridomestic Aedes aegypti. Because MS can loft large quantities of larvicide over relatively long distances, we examined its efficacy in a tidal marsh habitat for controlling Ae. dorsalis. Liquid Vectobac 12AS larvicide, containing Bacillus thuringiensis israelensis, was applied at 1.16 liter/ha using a MS. Cards that change color when exposed to liquid were placed perpendicular to the path of the MS showed that the larvicide mist traveled up to 60 m from the MS and did not extend to 90 m. Use of the MS enabled a 4-fold increase in total hectares treated during 2020-21 relative to the prior 2 years without an increase in staff time. Notably, there was 83% reduction in the quantity of Ae. dorsalis larvae at 5 days posttreatment. Similarly, there was 63% reduction in adult female Ae. dorsalis that were collected in encephalitis virus surveillance traps from nearby communities relative to the prior 2 years. There were 2.3-fold fewer requests for service to address a mosquito problem from residents of communities that abut the tidal marshes, suggesting the applications had a positive impact on these communities. The MS offer an attractive alternative to hand treatments in tidal marshes where the use of unmanned aircraft or all-terrain vehicles is prohibited by national wildlife refuge managers.