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The mulberry Thrips Pseudodendrothrips mori Niwa (Thy; Thripidae) is introduced as the dominant species in the insect fauna of mulberry orchards in
the north of Iran during summer season. As a result of thrips infestation, the mulberry leaves reduce the quality as food for silkworm. The host preference
wc_s conducted on a complete randomized plot with four treatments, i.e. Kehmochi (KM), Kairyo-Nezumigaeshi (KN), Ichinose (1) and Shin-Ichinose
which are improved varieties present in the area. For this purpose, the insects were collected three times. Number of individuals in one cm2 of leaf area were
calculated as a density index. The results of statistical analysis with Duncun's new multiple range test (DMRT) indicates that the KM bearing an average
(+5E) of 3.48+0.3 insects is significantly different from the other treatments at 1 % level. Ichinose, bearing 2.2:t0.Ol stands second while KN and SI varieties each with 1.31 +0.06 and 1.07 +0.02 insects respectively, stand third.
Non-preference of this insect to different varieties in laboratory with poly choice test was studied. The preference percent of this species in four
varieties out of thirteen replications was 38.8, 29.38, 18.96 and 12.73 respectively. The results of statistical analysis in laboratory condition also
indicate that the KM is the most preferred variety and stands first while 51 with the least preference stands last and the other two varieties are intermediates. Considering combination of the laboratory and field results, the
KM variety is the most susceptible to mulberry thrips while 51 shows a relative resistance to this insect.