This study investigates the effects of diazinon, an organic phosphoric insecticide, puffing on salivary gland polytene chromosomes of Drosophila melanogaster. Adult flies are applied diazinon and F1 generations were developed. The third instar larvae's salivary glands polytene chromosomes were examined in F1 generation. Puff areas in polytene chromosomes are regions of RNA synthesis and provide information on interphase nucleus. Certain differences were detected in puffing model of polytene chromosomes following he diazinon application. These differences were either the retreat of certain active regions or the activation of certain band regions. Puffs in 1D, 4C, 22AB, 38B, 63F, 71F, 72D, 74C, 97A, 97E, 98A, 98D, and 98E band regions retreated with diazinon application. On the other hand, active puff areas were detected in 1E, 2D, 3AB, 7AB, 42E, 43F, 57EF, 58EF, 61CD, 67AB, 72AB, 82D and 88F band regions after diazinon application. Some differences were observed in puffing frequency in some puff areas. In conclusion, it could be said, that diazinon application changed the interphase nucleus mechanism in polytene chromosomes, and thus the developmental program.