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.
Subject(s)
Aedes , Bacillus thuringiensis , Animals , Female , Larva , Mosquito Control , Mosquito Vectors , Puerto RicoABSTRACT
Despite historical and contemporary evidence of its effectiveness, larval source management with insecticides remains little used by most malaria control programs worldwide. Here we show that environmentally safe biological larvicides under field conditions can significantly reduce anopheline larval density in fish farming ponds that have became major larval habitats across the Amazon Basin. Importantly, the primary local malaria vector, Anopheles darlingi Root (Diptera: Culicidae), feeds and rests predominantly outdoors, being little affected by interventions such as long-lasting insecticidal bed net distribution and indoor residual spraying. We found >95% reduction in late-instar density up to 7 d after the first application of VectoMax FG or VectoLex CG (both from Valent BioSciences), and up to 21 d after larvicide reapplication in fish ponds (n = 20) situated in the main residual malaria pocket of Brazil, irrespective of the formulation or dosage (10 or 20 kg/ha) used. These results are consistent with a substantial residual effect upon retreatment and support the use of biological larvicides to reduce the density of anopheline larvae in this and similar settings across the Amazon where larval habitats are readily identified and accessible.