Population Fluctuation and Spatial Distribution Pattern of Sesamia cretica Led. (Lepidoptera: Noctuidae) in Southeastern 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, 2017 and 2018. 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 4th and 8th October in Aminabad, 17th and 20th September in Talebabad, 6th and 17th September in Ahmadabad and Khaveh, in 2017 and 2018, respectively. Mean densities of the larvae per plant were 52.62±12.53, 10.50±2.85, 17.45±3.48, 7.57±1.55 in 2017 and 12.00±5.29, 1.00±0.30, 11.05±2.36, 12.00±3.41 in 2018 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 10-22 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 2018. According to Taylor’s power law, S. cretica in Ahmadabad and Aminabad in 2017 had a random pattern, while in all fields of the other regions it had an aggregated spatial distribution during 2017 and 2018. In Iwaochr('39')s model, the regression between the mean crowding and the density was not significant in Aminabad and Khaveh in 2017 and Talebabad in 2018, 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.