An evaluation of Bacillus thuringiensis israelensis (AM65‐52) treatment for the control of Aedes aegypti using vehicle‐mounted WALS® application in a densely populated urban area of Puerto Rico

Abstract

BACKGROUND With a shortage of effective options for control of Aedes aegypti in Puerto Rico due to widespread resistance to conventional mosquito adulticides, an alternative approach was investigated to reduce vector populations. In two areas (totaling 144 ha) of the municipality of Bayamón, Puerto Rico, Bacillus thuringiensis israelensis (Bti) AM65‐52 WDG was applied at a rate of 500 g/ha using vehicle‐mounted aqueous wide‐area larvicide spray applications weekly for 4 weeks and then every other week for a further 16 weeks. Bioassay jars were placed in the field to monitor for deposition of Bti droplets in open spaces, and under vegetation and building coverage. Autocidal gravid ovitraps were placed throughout the field site to monitor the population of adult female Ae. aegypti in both treatment and control sites. RESULTS Larvicide spray was successfully deposited into jars in an array of open and covered locations, as confirmed by larval bioassays. After the fourth weekly spraying, differences in autocidal gravid ovitrap densities were observed between treatment and control sites resulting in 62% (P = 0.0001) and 28% (P < 0.0001) reductions in adult female Ae. aegypti numbers. CONCLUSION Repeated wide‐area larvicide spray application of Bti AM65‐52 WDG to residential areas in Puerto Rico effectively suppressed dengue vector populations. The success of this trial has led to expansion of the WALS® program to a larger area of Bayamón and other municipalities in Puerto Rico. © 2020 Society of Chemical Industry

Field evaluation of WALS truck-mounted A1 super duty mist sprayer® with VectoBac® WDG against Aedes aegypti (Diptera:Culicidae) populations in Manatee County, Florida

“…In the open-field analysis, droplets that caused over 70–100% morality in any of the rows had a mean VMD between 158 and 218 µm. Other successful truck-mounted mist applications have noted reduced Aedes populations when the droplet range was between 111 and 232 μm in areas that would otherwise be challenging to control with conventional mosquito control methods [ 26 , 30 , 46 ]. Conversely, a mean VMD of ≤ 84 μm or ≥ 467 μm resulted in almost no mortality.…”

“…This could be due to the layout of buildings and landscapes which potentially affected the spray cloud and obstructed the product from reaching the larvae. Two different bioassay jars treated under identical conditions, under sparse vegetation for example, can reach different levels of mortality [ 30 , 31 ]. Wind direction and wind speed could have also impacted mortality in the bioassay jars.…”

“…israelensis (strain AM65-52) containing 3,000 International Toxin Units (ITU) per milligram of product. This product was chosen because it consists of only Bti and food-grade (U.S. EPA list 4) inert ingredients as well as the environmental profile, high target specificity, fast results; mortality typically occurring within 2–24 h and no record of insecticide resistance to this active ingredient by target mosquito populations [ 19 , 26 , 28 , 29 , 30 ]. VectoBac WDG is registered for direct application in cryptic water holding containers, the preferred oviposition sites of Ae.…”

“…The Micronair atomizer uses a rotating wire gauze cylinder to produce spray droplets in the extremely fine to fine (EF/VF/F) size classification ensuring the ideal droplet spectrum for the bio-larvicide. The Micronair is driven by airflow from three 69.85 mm fan blades set at 55 degrees [ 30 ] that can be adjusted to produce the correct droplet size for a particular application and a 20-mesh screen. The A1 mister has a 379 L polyethylene tank and a 20 hp twin cylinder electric start Honda GX 630 engine (Honda Engines Group, Alpharetta, Ga).…”

“…The placement of the bioassay jars was to simulate the presence of Ae. aegypti larval habitats and the potential for the droplet cloud to fall in those habitats [ 30 ]. A total of 50 polystyrene 177 oz bioassay jars per replicate were placed in the field the afternoon of application at fixed locations.…”