an investigation into appropriate sample unit and sample universe to estimate tetranychus urticae koch. population in common bean (phaseolus vulgaris l.) fields in north of lorestan province

two-spotted spider mite, tetranychus urticae koch. is one of the most harmful pest of common bean in most areas of iran, including lorestan province. the appropriate unit and universe sampling of mite population were investigated in common bean fields in borujerd, dorud and azna in 2008. the results showed that samples should be taken from top, middle and bottom of the plant height. in addition, comparison of three sample units, 3 half leaves per plants (a half leaf from each plant height), 3 leaves per plants (a leaf from each plant height) and 6 leaves per plants (two leaves from each plant height) revealed that there was no significant difference between cv and rv of each female and nymph populations in related to cv, rv and rnp parameters. however, sample unit with 3 half leaves, with the highest amount of rnp, showed a significant difference compared with 3 and 6 leaves. based on the findings of this research, sample unit with 3 half leaves (three half leaves of alternately left and right from three different plant height) is recommended in the sampling of t. urticae populations in common bean fields.