A review of DDT resistance as it pertains to the 91-C and 91-R strains in Drosophila melanogaster.

While insecticide resistance presents a challenge for those intent on controlling insect populations, these challenges have also generated a set of tools that can be used to ask fundamental biological questions about that resistance. Numerous species of insects have evolved resistance to multiple classes of insecticides. Each one of these species and their respective resistant populations represent a potential tool for understanding the molecular basis of the evolution of resistance. However, in-laboratory maintenance of resistant insect populations (and their comparative susceptible populations) suitable for asking the needed set of questions around the molecular consequences of long-term pesticide exposure requires a significant, in places prohibitive, level of resources. Drosophila melanogaster (hereafter referred to as Drosophila) is a model insect system with populations easily selected with pesticides and readily maintainable over decades. Even within Drosophila, however, few populations exist where long-term pesticide selection has occurred along with contrasting non-selected population. As such, the Drosophila 91-C and 91-R populations, which exhibit insecticide resistance to DDT (91-R), compared to a non-selection population (91-C), represent a unique resource for the study of high level DDT resistance. Moreover, with the availability of "omics" technologies over the past several decades, this paired population has emerged as a useful tool for understanding both the molecular basis of pesticide resistance and the molecular consequences of long-term pesticide exposure. In this review, we summarize the studies with these aforementioned populations over the past several decades, addressing what has been learned from these efforts.