104 - A Comparison of the Topical Application Assay and the CDC Bottle Bioassay Kit in Culex quinquefasciatus Mosquitoes from New Orleans, Louisiana.

Abstract: Monitoring the development of insecticide resistance and identifying mechanisms and risk factors that confer resistance in a vector mosquito population are crucial to an integrated mosquito management program. The first step of an insecticide resistance monitoring program is to screen for insecticide susceptibility. There are various screening methods available.
The objective of this study was to screen local adult Culex quinquefasciatus mosquitoes throughout Orleans Parish, Louisiana for insecticide resistance by comparing a topical application assay and the Centers for Disease Control and Prevention’s (CDC) bottle bioassay kit.  In 2021, wild-type Cx. quinquefasciatus egg rafts were obtained from 13 sites within Orleans Parish, LA. Adult mosquitoes that emerged from those egg rafts were screened for susceptibility to bifenthrin, deltamethrin, malathion, and naled, using technical grade active ingredients.
Results from these two assay methods were compared to assess the association between susceptibility outcomes. For topical assays, the mean mortality at 24 h of adult wild-type Cx. quinquefasciatus mosquito populations at all 13 sites was 28% for bifenthrin, 26% for deltamethrin, 35% for malathion, and 87% for naled. For the CDC bottle bioassays the mean mortality at the diagnostic time of adult wild-type Cx. quinquefasciatus mosquito populations at all 13 sites was 16% for bifenthrin, 7% for deltamethrin, 63% for malathion, and 95% for naled. In conclusion, both assays can detect insecticide resistance, however the results are not uniformly correlated.