Mosquito Control Activities During Local Transmission of Zika Virus, Miami-Dade County, Florida, USA, 2016

Janet C. McAllister; Mario Porcelli; Johana M. Medina; Mark J. Delorey; C. Roxanne Connelly; Marvin S. Godsey; Nicholas A. Panella; Nicole Dzuris; Karen A. Boegler; Joan L. Kenney; Linda Kothera; Lucrecia Vizcaino; Audrey E. Lenhart; John-Paul Mutebi; Chalmers Vasquez

Disclosures

Emerging Infectious Diseases. 2020;26(5):881-890. 

In This Article

Insecticide Resistance

Laboratory Assays

The insecticide resistance status of Ae. aegypti mosquitoes in Miami-Dade County was not known at the beginning of the outbreak. At the same time that the intensified mosquito control activities began in Wynwood and Miami Beach, Ae. aegypti eggs and adults were collected to evaluate their susceptibility to the active ingredients found in various commercial adulticide products, including those routinely used by the MCD. Eggs were reared in an insectary at 27°C and 80%–90% humidity, with 14 h daylight, and the resulting adults were used in the laboratory bioassays. CDC bottle bioassay[8] was performed using technical-grade permethrin, 43 μg/bottle; deltamethrin, 0.75 μg/bottle; etofenprox, 12.5 μg/bottle; sumithrin, 20 μg/bottle; naled, 2.25 μg/bottle; and malathion, 400 μg/bottle. Bottle concentrations and threshold times were based on prior calibration of the assay as described previously.[8] All technical-grade insecticides came from ChemService Inc. (https://www.chemservice.com). Ae. aegypti Orlando strain mosquitoes were used as a susceptible comparison colony. This colony was started in 1952 at what is now the US Department of Agriculture's Agricultural Research Service, Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL, USA). The CDC bottle bioassay revealed high levels of resistance to all synthetic pyrethroids at the diagnostic time; sumithrin (3%–14% death), etofenprox (1%–7% death), permethrin (2%–12% death), and deltamethrin (5%–65% death). We found no resistance to malathion or naled (Table 2).

Field Assays

Because resistance in laboratory assays does not directly translate to product failure in the field, we field-tested commercial products to find the most efficacious pyrethroid product for use in truck-mounted ULV spraying. The MCD used the midlabel rate (Table 1) for product application before and early in the outbreak. Mosquitoes collected in BG sentinel traps were held in a BugDorm2 Insect Tent (BioQuip, https://www.bioquip.com) and supplied with 10% sucrose until use in field testing. Field testing consisted of placing adult mosquitoes in cages, then exposing them to the commercial product applied at the mid-label rate with a truck-mounted Grizzly ULV Sprayer (Clarke, https://www.clarke.com). Cages were 7.6 m and 15.2 m from the road. Fifteen minutes after insecticide exposure, mosquitoes were transferred to clean holding containers (236.5-mL cardboard ice cream cups covered with netting) and given access to a 10% sucrose solution. Deaths were recorded 24 h after treatment (Table 2). Additional field testing was conducted using the highest label rate (Table 1) of DeltaGard (deltamethrin; Bayer CropScience LP, https://www.environmentalscience.bayer.com) and Zenivex (etofenprox; Central Life Sciences, https://www.centralmosquitocontrol.com). We chose Zenivex for additional testing because the wind appeared to shift direction during the initial application, causing the treatment to not fully reach all cages. We chose DeltaGard because it performed the best in both bottle bioassay and the previous field testing using the midlabel rate. DeltaGard was selected as the best performing product when applied at the highest label rate (0.00134 lb/acre) and was used for truck-mounted spraying in the northern Miami Beach and Little River red zones where aerial spraying did not occur.

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