Methoprene resistance in field <i>Aedes taeniorhynchus</i> (Diptera: Culicidae) populations from Indian River County, Florida

Methoprene has been employed to manage salt marsh mosquitoes, specifically Aedes taeniorhynchus, in the Indian River Mosquito Control District (IRMCD) since the mid-1970s. However, due to reduced effectiveness and significant increase in resistance among Ae. taeniorhynchus (Wiedemann) (Insecta: Diptera: Culicidae) to methoprene products, the use of methoprene for mosquito control in the IRMCD ceased in 2009. Given the current limited availability of safe, effective and affordable larvicide products, discussions have emerged about the potential reintroduction of methoprene-based products for Ae. taeniorhynchus control in the IRMCD. To determine the feasibility of methoprene product reintroduction in the field control operations, laboratory bioassays were conducted to assess the resistance status of Ae. taeniorhynchus populations from field collections directly. These bioassays involved exposing late 4th instar larvae of Ae. taeniorhynchus to technical grade methoprene. The results revealed varying levels of resistance to methoprene among 16 field Ae. taeniorhynchus populations for the last 2 yr. Our findings confirm that methoprene resistance persists in some of the local Ae. taeniorhynchus populations. The outcomes of this research will assist IRMCD in strategic decision-making regarding the utilization of methoprene products for future Ae. taeniorhynchus control measures.