From surveillance to control: Evaluation of a larvicide intervention against Ae. aegypti in Brownsville, Texas

South Texas is recognized as a potential area for the emergence and re-emergence of mosquito-borne diseases thanks to recent circulation of Zika (ZIKV), chikungunya and dengue viruses. During 2017, high Aedes aegypti mosquito abundance found in the city of Brownsville, TX, in combination with the previous year’s local transmission of ZIKV and continued risk, triggered the activation of the Texas Department of State Health Services (DSHS) Emergency Mosquito Control Contingency Contract. The contract was with Clarke Environmental and Mosquito Control and the response was to control Ae. aegypti populations using a wide-area larvicide spray (WALS™) of Bacillus thuringiensis israelensis ( Bti ). The WALS application was evaluated through a field-based bioassay and by analyzing surveillance data using a nonparametric comparison of mosquito abundance pre- and post-WALS application. The WALS application bioassay demonstrated that the larvicide affected larval habitats up to 60 m into the target properties. Additionally, the number of Ae. aegypti captured in traps decreased in the WALS intervention areas compared to the control areas with an estimated 29% control.