Abstract:

Migration of susceptible individuals from untreated areas to populations that have developed insecticide resistance is one of the most important processes that can significantly delay or even prevent the development of resistance against insecticides. Fitness parameters of susceptible and resistant insect populations and changes in fitness following susceptible population migration have a crucial place in this process, as they determine the permanence and spread of susceptible alleles in the absence of insecticides. In this study, we investigated changes in resistance levels and fitness characteristics after introducing individuals from the ancestral susceptible strain in an equal ratio to a housefly (Musca domestica) strain artificially selected against fenitrothion, an organophosphate insecticide. We measured fitness parameters such as pre-adult development time, fecundity, fertility, and survival. Compared to the susceptible strain, the resistant strain had slower development time, but there were not any significant differences for fecundity, fertility, and survival. The level of resistance decreased gradually with 2 generations of susceptible migration. Development times were faster in both migration strains compared to the resistant strain. In addition, we detected a fitness reduction in fecundity, fertility, and female survival after the first generation of migration, but this reduction was alleviated after the second generation of migration. In conclusion, these findings indicate that fenitrothion resistance in Musca domestica has important fitness costs related with development time, and these costs are mitigated with susceptible migration.

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