The plum bud gall mite, Acalitus phloeocoptes (Nalepa) is a pest of Rosaceae plants. The feeding activity of this mite create galls around buds. Adult A. phloeocoptes overwintering females survive in the hardened galls as the infective population for the next year. After the serious damages observed in plum trees of Miandowab region, sampling was done and the pest identified as A. phloeocoptes. No economic damage was disclosed in Iran before and it seems the mites spread very fast and the problem grows every year. So this mite biology must be investigated. Regarding the study of the survived mites in different side branches, on early January 2017, 100 branches of one or two years old in four sides including north, south, east and west of each plum trees of an orchard were marked with ribbon tapes as field-wintered group and another 100 branches were brought to the laboratory and stored in constant 5°C as laboratory-stored group. From 30 February to 24 March 2017, 12 branch sections were removed from laboratory cold-storage and 12 branches were collected from the orchard at two weeks intervals. A sticky-band trap was placed near the gall on
each branch and branches were placed at 15°C and 13:11 (L: D) h photoperiod. Traps were replaced every 24 hours and captured mites were counted using magnification 10 of Leitz LABORLUX S microscope until no more mites were trapped. Finally the total mites captured in each branch counted and a comparison between means for total emerged mites from the two group branches of different sides at each collection date was made using MSTATC software. The mean number of total mites emerged from field-wintered branches (592) was more than that in laboratory-stored
branches (111). It shows that the mites better survived in the field and constant 3°C is fatal for them. The comparison between means for total emerged mites from branches of different sides showed significant difference between them. The south side branches had more emerged mites (mean = 483.1) and the north and west branches grouped as the sides with lowest emerged mites (respectively 321.1 and 261.2). It was predictable and the more worm condition of the south branches in cold regions such as Miandowab were more favourable condition for the overwintering females, because in this region there are many winter days with sub-zero minimum temperatures that will kill many of them
