Fenvalerate acted as a toxic factor and repellent to the fruit fly (Drosophila melanogaster), its effect led to an increase in mortality at three Larval stages. The surviving hatched flies had a smaller body size and lower weight and laso laid fewer eggs. The reason for the smaller body measurements was probably the effect of fenvalerate on cell division, cell size, and cell numbers. The treated animals had lower DNA and RNA content because the cell number and size were reduced by fenvalerate treatment. The results show that the flies under stress conditions consume more energy and therefore have a reduced lipid, glycogen and protein content. We have noted that the RNA content and consequently the protein content was reduced in the cells, because if all the multiple sources of energy have been exhausted, proteins can be used as more energy is required, which supports the m-RNA Protein formation. The metabolism of glycogen and lipids was controlled by AKH, so the glycogen and lipids were degraded and reduced in treated animals. The release of AKH accelerated the heartbeat of the Pupae. Fenvalerate and starvation affected the morphological parameters, these effects had physiological causes. The next generation was affected because of fenvalerate residues on male and eggs were loaded into the F1. However, the transferred amount was not enough poison to result in a great damage. According to the morphological results, we expected that Epigenetic effects could be behind these results, thus Isogen-lines were imlpemnted to detremine this suspected effects. This theory, however, was not confirmed. We assume that the morphological and physiological effects were caused by hunger and stress, these effects have no genetic causes. It is expected that the next generations F2 and F3 would be normal. In this study, difficulties were encountered, such as the determination of the sublethal dose range and finding the right treatment method (dipping in gift or treating with contaminated food).