Spatial dispersion and fixed-precision sequential sampling of black bean aphid, Aphis fabae (Hem.: Aphididae) in a sugar beet field

The black bean aphid, Aphis fabae Scopoli (Hemiptera: Aphididae) is an important pest of sugar beet fields in Khuzestan province. Knowledge about economic and precise sampling program can play critical role for developing integrated pest management (IPM) program of this pest. In this study, the spatial distribution of the pest was investigated in a research sugar, 1 ha, beet field of Shush district, and a fixed-precision sequential sampling program for estimating the aphid density was developed. Samplings were performed every 3 days and spatial distribution of this pest on sugar beet plants was evaluated using two models, Taylor's power law and Iwao's patchiness. The pest distribution on sugar beet plant was aggregated and Taylor's power law provided better fitness to the spatial distribution data of this aphid on sugar beet plants. Therefore, The Green's model was used for developing fixed-precision sequential sampling of the aphid. Based on the pest density, the optimum sample size ranged from 99-130 plants or 16-21 plants at desired precision level 0.1 or 0.25, respectively. Calculated stop lines implicated that the sampling has to be continued till the aphid cumulative number per sugar beet plant reach to 10 at precision level 0.25. The stop line was 25 aphids at precision 0.1.