Fixed precision sequential sampling plans of two spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) in Phaseolus vulgaris L. Fields

Two spotted spider mite, Tetranychas urticae Koch is one of the most important pests of common bean, Phaseolus vulgaris L. fields in most regions of Iran. To deploy the appropriate management of this pest, in common bean fields, we need to construct a sampling plan that allows estimate population density quickly and accurately. During 2011-2012, spatial distribution and fixed precision sequential sampling plans of T. urticae population were investigated by the use of different sample unit sizes, in common bean fields in north of Lorestan province (Borujerd, Dorud and Azna). Regarding to the fitting of data with Taylor's power law, parameters of this method were used to develop the enumerative sequential sampling plans for each sample unit. Results showed that Taylor's b was significantly greater than 1, for all the life stages, indicating that T. urticae populations were aggregated. Comparison of Taylor's b for larvae, nymphs and adults, showed no significant difference among them. Therefore, Taylor's b and α re-estimated for total number of larvae鼩ꦆ쾚盩, without separating them. Sample size curves were calculated and compared at 10%, 15% and 25% levels of precision. Also, for each sample unit, Green's fixed precision sequential sampling plans were validated using 12 independent data sets. Validation results of these models showed that to achieve a precision of 0.25, which is generally accepted in IPM programs, it is necessary to take samples with an average sample number (ASN) of 146, 102 and 86 for sample units of 2, 4 and 6, respectively. In conclusion, the developed enumerative sequential sampling plans at precision level of 25% was recommended for monitoring this pest in irrigated common bean fields.