In late July, months after news of the Zika outbreak in South America started to make headlines in the U.S., the first locally acquired Zika cases in the continental United States were confirmed in Miami-Dade County. By August 31, the Centers for Disease Control (CDC) had confirmed 35 cases of locally-acquired Zika in Florida.
With the health and economic well-being of the region suddenly at risk, the Miami-Dade County Mosquito Control program was abruptly thrust into the spotlight. Not only were its citizens calling for the most effective container-mosquito control interventions available, the eyes of the nation were trained on Miami-Dade to see how it would respond and how effective that response would be.
Like other programs in Florida, the majority of Miami-Dade County’s mosquito control program was based on insecticides that target adult mosquitoes (adulticides). Since adult mosquitoes transmit disease, the rationale for treating primarily with adulticide is not uncommon. But the pressing health crisis in Miami prompted officials to add new applications of biological larvicides which target immature mosquitoes Building on new application technology and promising results seen in neighboring districts, Miami-Dade control officials expanded the breadth of its Integrated Vector Management (IVM) program by scheduling wide area sprays of bacterial larvicides through September.
Over the course of six weeks, the local government elected to spray a two square mile area in Wynwood, FL with both an organophosphate adulticide and Bacillus thuringiensis subsp. israelensis, strain AM65-52 (Bti). The integrated approach targeted adult mosquitoes with the conventional insecticide and immature mosquito populations with Bti. Outside of the two square mile area, the organophosphate was used as a stand-alone control.
The Miami Herald was among the first to report the dramatic results in the larvicide plus adulticide treated area. “In areas without the larvicide, the adult populations are rebounding much quicker and much higher than in the area (treated) with both,” Janet McAllister of the Centers for Disease Control and Prevention was quoted as saying. Field scientists from Valent BioSciences Corporation (VBC), who consulted in the Bti applications, say their data confirms what was reported by the Herald.
“As we anticipated, the bioassay results following the August 17th wide-area larvicide spray application over Wynwood are telling,” said Peter DeChant, Global Technical Manager for Public Health and Forest Health at VBC. “They’re consistent with data generated since 2010 in the Florida Keys and in similar programs abroad over the last several years.”
VBC jar bioassay from an aerial spray on August 17, 2016 showed mosquito larval mortality within the area was at or approaching 100% from 24 to 48 hours after the VectoBac WDG (Bti) application. Even in jars that were completely obstructed by foliage or other physical barriers, larvae mortality stood at 85% after 48 hours (see Graph).
DeChant says the Miami-Dade results reconfirm data published or under manuscript review from three separate studies conducted by mosquito control professionals on trial work surrounding use of VectoBac WDG for container mosquito control in urban areas. Andrea Leal, recently appointed director of the Florida Keys Mosquito Control District (FKMCD) and co-author on the Florida Keys study, was director of operations in 2010 when wide area spray applications of VectoBac WDG began in response to a dengue outbreak. Leal and her team worked closely with VBC scientists to calibrate their equipment and become the first mosquito control district in North America to use the new larvicide application method, which was adapted from aerial spray platforms in forestry.
“Aedes aegypti is a formidable adversary, especially for a district of our size,” says Leal. “These mosquitoes gravitate toward cryptic breeding sites that are difficult and time consuming to locate. Once we were able to ‘dial-in’ our equipment and get the droplet size right, we found we were delivering larvicide into even the hardest-to-reach areas, opening doors for our staff to focus on larger breeding sites. Bti gave us another valuable tool that helps our program while saving us time and resources.”
Controlling the container mosquitoes is only part of the challenge, however. Leal notes that complementing control tactics with a well-thought-out public relations strategy helps keep stakeholders informed on what the control measures are, and why they’re being employed.
“My advice to other districts is that there are three things that will make your aerial spray program a success “, Leal says, “First, you need a good public relations team to help explain what you’re doing and why. Second, you need to provide your community with a list of things they can do on the ground to help overcome the challenge. Third, you need to be committed to your trial work. We worked long and hard over several weeks to get the setup that we have now. But it pays off in the end. We achieved control and don’t get phone calls when we spray asking what’s going on. It makes you feel good about what you’re doing.”
