This experiment was conducted to evaluate resistance of pure lines of silkworm Bombyx mori L.against the pathogen of white muscardine disease. In this experiment that was accomplished in summer and autumn, 1999, seventeen commerical pure lines including 10 japanese and 7 chinese were employed. A completely randomized design with 5 replications for each treatment was used. The economical traits i.e. vitality of larvae, pupae and moths, percentage of muscardine infection, number and percentage of the best, middle, low and double cocoons, weight of single cocoon, cocoon shell weight, percentage of cocoon shell, the best cocoons’ yield and larval duration were recorded and analysed. From the obtained results, lines 101433-6 and 107 significantly (P?0.05) showed the higest vitality of larvae. Line 107 significantly (P?0.05) showed the highest vitality of pupae. Furthermore lines 110 and 107 significantly (P?0.05) showed the higest vitality of moths. Line 107 significantly (P?0.05) showed the highest number of produced cocoons. Likewise line 32 significantly (P?0.05) had the superior performance in comparison whit other lines from the viewpoint of single cocoon weight. Also lines 114 and 32 significantly (P?0.05) showed the highest cocoon shell weight. Furthermore line 114 showed the highest percentage of cocoon shell significantly (P?0.05). Likewise lines 112 and 107 significantly (P?0.05) had the superior average of the best cocoon yield. Furthermore correlation coefficient whitin number of live larvae and pupae
(r = 0.720**), number of live pupae and moths (r = 0.930**), percentage of muscardine infected pupae in 7th day after spinning and at emergence (r = 0.934**) and percentage of vitality of pupae in 7th day after spinning and emergence (r = 0.902**) were significant.
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