Abstract
Striped rice stem borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae) is a major pest of rice in northern Iran. Regarding to the importance of population dynamics studies in pest management programs, the population fluctuations of C. suppressalis was studied in central part of Mazandaran province (Rice Research Centre of Mazandaran) during 2005-2006. The male and female moths were firstly observed in 9th and 19th May 2005, and 29th April and 9th May 2006, respectively. The first egg masses and larvae were collected in 30th May and 10th June 2005, respectively. C. suppressalis had three generations in central part of Mazandaran province, which the peak of density was observed at 9th June, 20th July, 23rd August, respectively in 2005, and 5th June, 20th July and 16th August in 2006. The highest population density of both males and females moths in 2005 was observed in the 2nd generation, while the first generation had the highest population density than the 2nd and 3rd ones in 2006. The highest population density of egg masses was counted for the 1st generation (22±6 egg masses), and were 14±4 and 11±3 egg masses for the 2nd and 3rd generations, respectively. The generation time in 2005 was 40, 20, and 25 days for the 1st, 2nd and 3rd generations, respectively, and 40, 30, and 20 days in 2006. Captures of moths in light traps through 20th April until 20th August 2005 indicated that the male counts were more than the females at the beginning of the first and second generations, but the sex ratio gradually deviated toward females. In this research, the climates' effect on the population fluctuations of different life stages of C. suppressalis was evaluated too.

Keywords: Population fluctuations, Striped rice stem borer, Chilo suppressalis, Mazandaran