R. Arbabtafti - Department of Entomology, Faculty of Agriculture, Tarbiat Modares University, P. O. Box: ۱۴۱۱۵-۳۳۶, Tehran, Islamic Republic of Iran.
Y. Fathipour - Department of Entomology, Faculty of Agriculture, Tarbiat Modares University, P. O. Box: ۱۴۱۱۵-۳۳۶, Tehran, Islamic Republic of Iran.
H. Ranjbar Aghdam - Iranian Research Institute of Plant Protection, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran.

Population density and dispersion pattern of Sesamia cretica Led. was determined in maize fields in Varamin (Ahmadabad and Khaveh) and Rey (Aminabad and Talebabad) areas (Tehran, Iran) during two agricultural seasons, ۲۰۱۷ and ۲۰۱۸. A whole plant of maize was selected as a sampling unit to estimate the number of S. cretica larvae. The highest population density of S. cretica larvae per plant was recorded on the ۴th and ۸th October in Aminabad, ۱۷th and ۲۰th September in Talebabad, ۶th and ۱۷th September in Ahmadabad and Khaveh, in ۲۰۱۷ and ۲۰۱۸, respectively. Mean densities of the larvae per plant were ۵۲.۶۲±۱۲.۵۳, ۱۰.۵۰±۲.۸۵, ۱۷.۴۵±۳.۴۸, ۷.۵۷±۱.۵۵ in ۲۰۱۷ and ۱۲.۰۰±۵.۲۹, ۱.۰۰±۰.۳۰, ۱۱.۰۵±۲.۳۶, ۱۲.۰۰±۳.۴۱ in ۲۰۱۸ in Aminabad, Talebabad, Ahmadabad, and Khaveh, respectively. The population of captured male adults in all fields in the second year was less than the first one. Peak numbers of male moths had a difference of ۱۰-۲۲ days between the two studied years. Based on the index of dispersion, the spatial distribution of S. cretica larvae in all fields in both areas was aggregated during the two years of study, except for Aminabad in ۲۰۱۸. According to Taylor’s power law, S. cretica in Ahmadabad and Aminabad in ۲۰۱۷ had a random pattern, while in all fields of the other regions it had an aggregated spatial distribution during ۲۰۱۷ and ۲۰۱۸. In Iwao's model, the regression between the mean crowding and the density was not significant in Aminabad and Khaveh in ۲۰۱۷ and Talebabad in ۲۰۱۸, while in the other fields indicated the aggregated spatial distribution. The lowest estimate of the sample size was computed by using Taylor’s power law. The results revealed that population fluctuation of S. cretica was affected by the region, but in spatial distribution pattern, the oviposition behavior of the pest was a much more determining factor than the region. The coefficients of the spatial pattern can be used for improving the sampling program to calculate the population density of S. cretica precisely.

Dispersal pattern, Maize, Pink stem borer, Population density.