Investigation on Spatial Dispersion of Sugarcane Pink Stem Borers Sesamia spp. (Lep.: Noctuidae) in Sugarcane Fields

Sugarcane pink stem borers, Sesamia spp., are the key pests of sugarcane in the south of Khuzestan province, Iran. These pests damage heavily the sugarcane crop and sugar product every year. In this research, spatial dispersionof the stem borers populations were studied in three sugarcane fields (25 hectare each, Cp69-1062 cultivar) in 2008. Sampling was carried out monthly in seven stages. External symptoms of pest damage were used as a population indicator and the number of infested stems and internodes of sugarcane were recorded in each sampling station. In order to determine the type of pest spatial dispersionin these three fields, various classical statistics indices were used. In all sampling stages, values of the variance to mean proportion index, index of Patchiness and Morisita’s index were significantly higher than one, and values of 1/k index and Green’s index were higher than zero. The obtained results of all indices indicated that spatial dispersionof Sesamia spp. was aggregated. The regression coefficients of Taylor’s power law b and Iwao’s β were determined 1.45±0.065 and 1.18±0.031, respectively. Thus, they had significant difference from one, and both indicated the aggregated spatial dispersionfor the pest life. Based on R2 and P-values of regression analysis, Iwao’s patchiness showed a better fitness for pest spatial dispersiondata in comparison with Taylor’s power law.