Impacts of an Organophosphate and a Pyrethroid on Insecticide Resistance in Culex Quinquefasciatus (Diptera: Culicidae)

Abstract

Environmental security is a large part of public health. While an abundance of research has been done to assess insecticide resistance in adult mosquitoes, there is a general lack of information about the potential effects of insecticide exposure on immature (i.e., larval) mosquitoes. Chemical control and reducing the number of larval habitats are two of the most successful ways to keep mosquito populations under control. In this project, we investigated whether exposure to sub-lethal doses of insecticides at the larval stage impacted insecticide resistance in mosquitoes at the adult stage using a colony of insecticide-susceptible Culex quinquefasciatus mosquitoes obtained from the Centers for Disease Control and Prevention (CDC). Approximately 10 larvae/well were placed into a six well plate. Ten six well plates were used for each group (total of 30 plates) and filled with tap water that had been inoculated with insecticide. Two different types of insecticides were used: Fyfanon® (organophosphate; active ingredient [AI] malathion) and Biomist® (pyrethroid; AI permethrin). A control group not exposed to any insecticides was also included. Once the larvae had developed into adults, a CDC bottle assay was completed to determine the extent to which adult mosquitoes were resistant or susceptible to the insecticides. Following the CDC bottle bioassay protocol, the number of dead mosquitoes was recorded at several pre-determined time points for up to two hours. This was done for all three groups. After the bottle bioassay was completed, a line graph was made for visual interpretation of data. For the mosquito population tested here, mosquitoes exposed to insecticides as larvae were more likely to be susceptible to the insecticides as adults.