Investigations on the population fluctuation of olive pyralid, Palpita unionalis (Hübner) (Lepidoptera: Pyralidae) in olive groves in Bursa Province of Turkey This study was conducted to determine the population fluctuation of Palpita unionalis (Hübner) (Lepidoptera: Pyralidae), and to provide essential fundamental biological data for managing this pest in olive groves in Bursa during 2001 and 2002. Studies were carried out at weekly intervals in each olive grove, Gölyazı, Kumyaka and Gündoğdu, which were located at three ecological areas. Population fluctuation of larvae was monitored by counting larvae on a total of twenty shoots (25 cm long) collected at different heights from ten trees at each olive grove. In conclusion, it was determined that P. unionalis larvae appeared on late July or early August and had three peaks in August, September and October or November in both years at the olive groves of Bursa. During late July and late December, the olive pyralid gives 2 complete and 1 partial generations in the olive groves. Additionally, the larval populations surprisingly increased during October-November and the populations showed a decreasing trend during the average temperatures around the lower threshold temperature (9 ºC) for P. unionalis, in late November. P. unionalis unable to complete third generation overwintered as last larval instar in late December