We studied the dispersal and colonization of the European beech bark beetle Taphrorychus bicolor (Coleoptera, Scolytidae) in beech forests of Germany (Westerwald) and Slovakia (Kovacova). Mainly we focussed on the activity of male and female beetles emerging from the breeding material. In adition, we paid attention to unsuccessful colonizations of males alighting on beech trees (Fagus sylvatica). We found significantly higher proportions of males in April (p < 0.01, Westerwald; p < 0.05, Kovacova) but not in May (p > 0.05, both sites). Unsuccessful colonizations of Taphrorychus bicolor males were observed in the stems of all dying trees studied (n = 8) and their proportion in particular trees ranged from 10.6% to 33.8%. Unsuccessful colonizations occurred because T. bicolor males died (21.5%) or moved to other breeding sites (78.5%). Mortality of male beetles may have occurred because of a defence response of beech trees to the attacks and predation by Nemosoma elongatum (Coleoptera, Trogositidae).