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Adult Control and Insect Resistance Challenges

Adult Control and Insect Resistance Challenges

96 - Determining the Insecticide Resistance Status of Culex pipiens s.l. collected in Clark County, Nevada

Wednesday, March 5, 2025
8:30 AM – 8:40 AM AST
Location: 208 B
Abstract: West Nile virus (WVN) was first identified in mosquito and human populations of Clark County, Southern Nevada in 2004. In response to this public health threat, the Southern Nevada Health District (SNHD) developed a mosquito disease surveillance program to survey mosquito populations for arboviral diseases. In 2024, Southern Nevada experienced its greatest WNV burden to date, with 26 human cases and 388 WNV positive pools of 12,033 mosquitoes from 46 zip codes. With increasingly unpredictable climate patterns, it is important for the SNHD to develop a strategy to mitigate future arbovirus epidemics in Clark County, including mosquito abatement. This study determined the susceptibility status of Culex pipiens sensu lato (s.l.) collected from 4 jurisdictions in Clark County, to public health adulticides (deltamethrin, malathion and permethrin) and larvicides (Bacillus thuringiensis subspecies israelensis; Bti, Lysinibacillus sphaericus; LS, temephos and spinosad), using standardised CDC resistance intensity bioassays and WHO larval bioassays, respectively; the susceptible strain Culex quinquefasciatus JHB was assayed in parallel. In Clark County, highly intense pyrethroid resistance was evident, with surviving Cx. pipiens s.l. following 24 hours of exposure to 100X diagnostic dose of deltamethrin and permethrin; by comparison high to complete susceptibility was observed to the diagnostic dose of malathion. The resistance ratio 50s (RR50) were1.45 [95% CI: 1.03-2.04] and 1.63 [95% CI: 1.24-2.13] for spinosad and temephos, respectively. Complete mortality of Cx. pipiens s.l. was achieved using 150mg/L or 69.28 µg/ml of Bti or LS, respectively. Study findings provide the first comprehensive insecticide resistance monitoring efforts in Clark County and an important baseline for prospective control activities in the region.