Insecticide resistance of Miami-Dade Culex quinquefasciatus populations and initial field efficacy of a new resistance-breaking adulticide formulation

Authors: UNLU, ISIK - Miami-Dade County'S Mosquito Control; BUCKNER, EVA - University Of Florida; MEDINA, JOHANNA - Miami-Dade County'S Mosquito Control; VASQUEZ, CHALMERS - Miami-Dade County'S Mosquito Control; CABRERA, AIMEE - Miami-Dade County'S Mosquito Control; Estep Iii, Alden

Submitted to: PLOS Neglected Tropical Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2023
Publication Date: 12/12/2024
Citation: Unlu, I., Buckner, E., Medina, J., Vasquez, C., Cabrera, A., Estep Iii, A.S. 2024. Crouching Tiger, Obvious Trouble: Insecticide resistance of Miami-Dade Culex quinquefasciatus populations and initial field efficacy of a new resistance-breaking formulation. PLOS Neglected Tropical Diseases. 19(2). https://doi.org/10.1371/journal.pone.0296046.
DOI: https://doi.org/10.1371/journal.pone.0296046

Interpretive Summary: Miami-Dade County, Florida is one of the largest urban areas in the US. Culex quinquefasciatus mosquitoes can transmit this West Nile Virus and human cases of this virus are regularly reported in Miami-Dade. Effective control of these mosquitoes is critical for maintaining public health but insecticide resistance can challenge mosquito control operations. In this study, we broadly examined the extent of insecticide resistance to both chemical classes of adulticide used in Miami-Dade. We further characterized the presence of a genetic knockdown resistance mutation that has been associated with resistance. Results showed widespread resistance to pyrethroids and more variable resistance to organophosphates. To find effective strategies to control these resistant mosquitoes, we tested a newly EPA approved multiple action adulticide. This new product provided a relatively effective option for control of these resistant populations. We show that even though local Miami-Dade populations are resistant to common insecticides, baseline insecticide resistance studies can identify populations that are susceptible to current tools. We also show the potential of new tools to control populations that are resistant.

Technical Abstract: Miami-Dade County, Florida is part of one of the largest metropolitan areas in the United States. Locally transmitted West Nile Virus cases, primarily vectored by Culex quinquefasciatus Say in Florida, are reported annually and increase sporadically. To facilitate more effective integrated vector management, we undertook a survey to determine the insecticide resistance status for 29 populations of Culex quinquefasciatus in Miami-Dade County. Miami-Dade County Mosquito Control employed a Geographic Information System (GIS Software) oviposition cup (OV) layer to display, manage, and store geographic coordinates and information on each deployed oviposition bucket. CDC Bottle bioassay testing was conducted from these field collected egg rafts at the proscribed diagnostic doses and diagnostic times for pyrethroids and organophosphates used by Miami-Dade Mosquito Control. We also determined the frequency of the 1014 knockdown resistance mutation for a subset of locations. We found that mosquitoes were resistant to permethrin (27 locations) and deltamethrin (28 locations) in all tested locations. Although the 1014F allele was widely found, 5 of 17 locations had no 1014F homozygotes even though phenotypic pyrethroid resistance was observed. Testing with organophosphates showed a range of resistance with 6 of 29 locations susceptible to malathion and 7 of 21 susceptible to naled. Notably, most populations from Southwest Miami-Dade County were resistant to both classes of active ingredient. We subsequently conducted a field trial of ReMoA Tri, a new EPA-approved multiple active ingredient formulation labelled for resistant mosquitoes against a mixed location field population of Miami-Dade Cx. quinquefasciatus. Average 24 hr mortality was 65.1 ± 7.2% but as expected with a slower acting insecticide, 48 hour mortality increased to 85.3 ± 9.1% indicating good control of these resistant Cx. quinquefasciatus. Data generated from this current study show that while resistance is common in local populations and this can likely jeopardize the efficacy of some adulticide treatments, effective options are available to maintain control during active diseases transmission in Miami-Dade County.