تغییرات فصلی و توزیع فضایی ساقه‏خوار ذرت Sesamia cretica Lederer (Lep.: Noctuidae) در شمال خوزستان

The stem borer, Sesamia cretica Lederer (Lep.: Noctuidae) is considered as one of the most important corn pests in most regions of Iran, which causes significant damage to this crop every year by feeding on the stem. In order to study the population density and dispersal pattern of this pest, sampling was done weekly from maize fields of Andimeshk and Shush regions (Khuzestan province), during two agricultural seasons of 2022 and 2023. In order to catch of S. cretica adults, a pheromone trap was used and for estimating the population of pest immature stages, the whole plant of maize was selected as the sample unit. Based on the population of captured moths, this pest had four generations per year on maize. In both sampling years, the activity of this pest in the field began in mid of April. The highest average population density of S. cretica per plant was recorded on 1 May (1.75±0.425), 9 July (3.94±1.161) and 18 October (2.4±0.516) in Andimeshk and on 2 May (1.76±0.489) and 20 August (0.16±0.077) in Shush in 2022 and on 8 May (1.3±0.382) and on 5 October (0.97±0.254) in Andimeshk and on 30 May (2.9±0.747) and on 11 September (0.66±0.214) in Shush in 2023. The most pest infestation was observed in Andimeshk and in the first year (F=6.779; df=105, 3; P<0.0001). Based on the indexes of dispersion (ID), Clumping (IDM), Green (Cx), Taylor’s power law and Iowa’s models, the spatial distribution of pest in all fields of both areas was aggregated during the two years of sampling. Only based on the Iowa’s model, S. cretica in Shush in 2023 had a random pattern. Also, Taylor's power low showed a better fit than Iowa’s model. The results of this study showed that S. cretica due to its multigenerational nature and high density had high potential to damage in maize fields and in this regards, the indexes of spatial distribution can be used for improving sampling programs to estimate the population density of this pest, precisely.