Abstract
House flies, Musca domestica L., are a worldwide nuisance known for carrying and transmitting pathogens. Their olfactory system aids in identifying decaying substances such as human- and animal generated wastes that they use as oviposition sites and food sources. House flies select sites for oviposition, or egg laying, and food by detecting pheromones present on conspecific eggs, appropriate nutrients in the substrate, and pheromonal attraction. However, their attraction to decaying organic substances and their ability to travel to other locations can result in pathogen transmission to humans and animals. Insecticide application remains the leading method for controlling house fly populations in an effort to mitigate pathogen transmission. However, dependence on insecticides has led to insecticide resistance evolution and off-target effects. Commercial insecticidal baits such as QuickBayt® offer a more targeted approach by exploiting the house fly olfactory system with an attractant lure that encourages feeding on the product. These products can be utilized with either localized bait stations or scattered in areas where adult house flies are observed. The latter of these methods results in the dissemination of insecticides into the substrates and potentially exposing developing house fly larvae. Studies conducted on the house fly have demonstrated that larval experience, such as pheromone introduction, can cause behavior modifications in the subsequent adult stage. Despite previous studies in other insects demonstrating the effects of larval experience on adult behaviors, the potential effects of house fly larval development in insecticidal bait contaminated substrates on subsequent oviposition preference are not known. This information is needed to identify a potential novel mechanism that may accelerate insecticide resistance evolution due to continuous selection pressure in two life stages within the house fly life cycle. Additionally, this is the first known attempt at introducing insecticides in house fly larval development. Therefore, a study was conducted to determine if house fly oviposition preference could be influenced by insecticidal bait exposure during larval development. For 12 generations, house fly larvae were exposed to progressively higher concentrations of the insecticidal bait, QuickBayt®, during larval development. Oviposition preference in this “Selected” strain was assessed after every two generations and compared to the concurrently maintained, unexposed “Parental” strain from which it originated. The results of this study demonstrated that exposure to insecticide during larval development did not cause a shift in oviposition preference towards substrates containing the insecticidal bait. Furthermore, house fly larval experience did not result in adult oviposition behavior change that would further accelerate insecticide resistance evolution due to an additional selection pressure opportunity on this off-target life history stage. The importance of these findings is far-reaching. For the first time, experiments have been conducted demonstrating that insecticide selective pressure during larval development, may not alter adult oviposition preference and therefore, is not a novel pathway for insecticide resistance evolution in the house fly. This finding lends support for the continued and commonplace method of scattering insecticidal bait products where house flies are observed. While the results of this study could be used to inform house fly management programs, efforts to include more focused application methods that will work to delay potential avenues for insecticide resistance evolution should be continued, as further research in this area is warranted.