The study will investigate the relative roles of the pattern of insecticide applications and mosquito movement in the evolution and propagation of resistance in wild-caught Aedes aeygpti mosquitoes. Programs relying on heavy use of insecticides are now used for control. The effectiveness of insecticide-based control strategies is being threatened by the evolution of insecticide resistance. Resistance has increased globally yet the mechanisms behind this spread are still largely unknown. Insecticide application exerts a selection pressure, yet this pressure is not constant in time or space. Additionally, mosquitoes can spread resistance to new areas as populations mix. These mosquitos are a major public health problem as they transmit multiple viral diseases including dengue fever, chikungunya, and zika virus. The research will have notable broader impacts as it informs insecticide resistance management and will be helpful in developing novel mosquito control strategies. The most common form of insecticide resistance in Aedes aegypti is driven by point mutations in the para-orthologous sodium channel gene, which confers resistance to pyrethroid insecticides. Named kdr for "knock-down resistance", these point mutations may carry a fitness cost, rendering the resistant individuals less fit in the absence of insecticide pressure. Variation in the location and timing of urban insecticide applications creates a patchy environment of insecticide-free refuges, where susceptible mosquitoes may gain a fitness advantage, and areas with insecticide, where only resistant mosquitoes survive. There is also variation in the quality of larval habitats, which leads to density-dependent competition between individuals for resources. Under this complex selection scenario, the relative fitness of genotypes may change based on the presence of insecticide or larval density. To better understand these dynamics, researchers will conduct cage experiments under semi-natural conditions to quantify the relative fitness of kdr genotypes exposed to all combinations of two different treatments: with versus without insecticide, and high versus low larval density. These experiments will contribute to understanding the selection dynamics of kdr in Aedes aegypti and help explain patterns of resistance frequencies observed in field populations over space and time.
