Unstable fipronil resistance associated with fitness costs in fipronil-selected Aedes aegypti L

Development of alpha-cypermethrin resistance and its effect on biological parameters of yellow fever mosquito, Aedes aegypti (L.) (Diptera: Culicidae)

Alpha-cypermethrin interacts with the sodium channel and causes nerve blockage in insects. It is used to manage Aedes aegypti (Linnaeus) (Diptera: Culicidae), a primary vector of dengue worldwide. It not only affects both target and non-target organisms, but overuse of this insecticide increases the chances of resistance development in insect pests. In this study, resistance development, biological parameters, and stability of alpha-cypermethrin resistance were studied in a laboratory-selected strain of Ae. aegypti. The alpha-cypermethrin selected strain (Alpha Sel) developed an 11.86-fold resistance level after 12 rounds of alpha-cypermethrin selection compared to the unselected strain (Unsel). In biological parameters, Alpha Sel and Cross1 (Unsel ♂ and Alpha Sel♀) had shorter larval durations compared to Unsel and Cross2 (Unsel ♀ and Alpha Sel ♂) populations. The pupal duration of Alpha Sel and both crosses was shorter than that in the Unsel strain. The relative fitness of Alpha Sel, Cross1, and Cross2 was significantly less than that of the Unsel strain. These results indicate that alpha-cypermethrin resistance comes with fitness costs. Moreover, the frequency of alpha-cypermethrin resistance decreased when the Alpha Sel population was reared without further selection pressure for four generations. So, resistance was unstable and reversed when insecticide pressure ceased. We concluded that the judicious and rotational use of different insecticides with different modes of action and the adoption of other IPM-recommended practices would suppress resistance development for more extended periods in Ae. aegypti.