Application of geostatistics in management of two spotted spider mite, Tetrantchus urticae Koch (Acari: Tetranychidae) in common bean fields

Two spotted spider mite، Tetranychus urticae Koch is the most important pest of common bean in most areas of Iran، including Lorestan province. In this study the geostatistical charachteristics of this pest were evaluated in Borujerd common bean fields in 2009. To do this research، two red common bean (Goli variety) fields that each one was about four hectares were selected. In each field، about 300 points (stations) were identified and marked. Sampling was started in mid July. At each station on three point of plant height (bottom، middle and top) three leaves were sampled. In the laboratory، the samples were observed and mite population density were counted with respect to each life stage. Results showed that the spherical model provided the best fit (based on r2-values) for the semivariogram data in 20 data sets out of 25 at the beginning of the pest attak in late July and early August. In this time، nugget/sill ratio was very low and by passing the time this ratio increased so that the spatial dependence among points decreased. Thus in August and early September more semivariogram curves fitted with the model of pure nugget effect and did not show any spatial corrdation among points selected in the fields. The effective range of spatial correlation of this pest were relatively high at the beginning of the pest attack. This range for adult females، nymphs and eggs were 357-641، 510-710 and 610-711 meters respectively. These distances were reduced by passing the time and by approaching end of season. Based on these results، application of geostatistics is recommended to monitoring and forecasting of two spotted spider mite، T. urticae in common bean fields at the beginning of the pest attack.