The results of long-term studies of the ability of the inbred population of Drosophila melanogaster living in a vegetable store to adapt to the genotoxic effect of a half-lethal dose of benzotriazole are presented. A part of the imago was taken from the population, afterwards they were bred on a standard fodder used for the Drosophila laboratory lines, this was done every ten years from 1980 to 2010. Female and male imago were separately subjected to a single exposure to benzotriazole in a semi-lethal dose. Surviving imago were retained for reproduce, so five generations were studied in each created micropopulation. In each generation in adults, the survival, fertility and number of induced DLM were analyzed.It was found that from 1980 to 2010 the population partially lost the ability to restore survival and fertility. The males were the most sensitive to these criteria. Benzotriazole induced the dominant lethal mutations during the analyzed years. Female imago were more sensitive to the mutagenic effect of benzotriazole than males. The maximum number of dominant lethals was always observed in the first generation of the micropopulation, each of the studied years. The number of induced mutations significantly decreased by the fifth generation, but was always higher than the level of spontaneously occurring dominant lethals in the imago of the original population not exposed to benzotriazole.