Larval Control II
Larval Control II
Methoprene has been employed to manage salt marsh mosquitoes Aedes taeniorhynchus in our district since the mid-1970s. Initially, it demonstrated outstanding efficacy, achieving mortality rates of 95-100% based on field pupal collection over a 20-year period. However, starting in 1993, its effectiveness began to decline, with some sites experiencing a decrease to approximately 70% mortality, despite no observed resistance. Around a decade later, signs of Ae. taeniorhynchus resistance to methoprene started to manifest, as indicated by testing conducted by our district scientists. The presence of resistance became prevalent in our Ae. taeniorhynchus populations. Consequently, in 2009, a decision was made to transition to different larvicides.
In the last decade, methoprene has not been utilized in our district for Ae. taeniorhynchus control. Due to the limited availability of larvicide products, discussions have ensued regarding the potential reintroduction of methoprene for Ae. taeniorhynchus control, primarily due to its cost-effectiveness and formulation, Altosand. However, prior to implementing methoprene for mosquito control, it is imperative to conduct testing to confirm the resistant status of Ae. taeniorhynchus to methoprene throughout the district.
The resistant status of Ae. taeniorhynchus to methoprene was assessed through laboratory bioassays utilizing field-collected larvae. A susceptible Ae. taeniorhynchus colony from the USDA-ARS lab was used as a control for comparison. The bioassay tests involved exposing late 4th instar larvae of Ae. taeniorhynchus (USDA) and field-collected specimens to methoprene technical material. The results indicated varying levels of resistance to methoprene in field populations of Ae. taeniorhynchus. Our findings confirm the existence of methoprene resistance in Ae. taeniorhynchus.