The European corn borer, Ostrinia nubilalis Hubner (Lepidoptera: Crambidae) is a polyphagous pest, has a wide range of host and damages to about 200 plant species. This pest primarily damages corn then second other crops. The pest damages have been observed in Sari rice farms, in recent years. The larvae feeding within the rice stems causes damage to the central buds, obtain dead heart and white heads. Pheromon traps are used to estimate the population of the pest, study of biology, behavior, the appearance time, flight peak, and end of the flight period, investigation the effect of pesticides, distribution and dispersion, mating disruption, and more important one in mass trapping of pest to reduce population and prevent damage. For the integrated pest management (IPM) of the O. nubilalis, population fluctuations of adult males were studied by using delta pheromone trap in the first 6 months of the two consecutive years, 2016-2017, in the rice fields of Sari, Mazandaran province. Ten pheromone traps (the Spanish company Econex) for every one hectare, were installed in early April each year, and the number of captured male insects was counted every three days. Delta trap's sticky floor covering was replaced every month, and pheromone capsules inside the trap were replaced every three months. After investigation the appearance period of insects, three flight peaks were occurred during the studied crop seasons, so that the moths of the first generation were trapped during 25 days in the second week of May to the first week of June, the second-generation during 28 days in mid-June until the second week of July and third generation during 63 days from late July to late September. The three flight peaks were recorded, in the third week of May, late June and the first week of September, respectively for three generations. The captured male insect’s population in two years of research was significantly different, so that in 2016, an average of 89 insects per trap were captured, while this amount reached 240 in 2017. With using these results, insect emergence time of adult insects are determined and can be programmed to control the pest.