Colonization of two alien ambrosia beetles (Coleoptera, Scolytidae) on debarked spruce logs

In June 1996, Norway spruce (Picea abies) trees growing in a managed mixed forest near Cologne, Germany, were felled and debarked. Several days after felling, the examined spruce logs had attracted 21 beetle species, of which the alien ambrosia beetle Xylosandrus germanus (Coleoptera, Scolytidae) pr edominated. Another ambrosia beetle, Gnathotrichus materiarius was much les s abundant. The effect of log diameter on X. germanus densities was negligi ble both in shady and sunny areas in bole diameter ranges of 19 cm to 33 cm and 33 cm to 38 cm, respectively (P > 0.05). In contrast, X. germanus dens ity was significantly higher in the log in the shade (P < 0.001). Flight ac tivity of X. germanus showed a distinct diel pattern with a peak before daw n when the temperature exceeded 17<degrees>C.