The impact of Medetera dendrobaena Kowarz (Dipt., Dolichopodidae) on bark beetles

Many natural enemies of bark beetles have been studied in central Europe. However, little is known about the impact that these natural enemies might have on developing bark beetle populations in the field. The larvae of Medetera dendrobaena are known to be important natural predators of bark beetles, especially in virgin forests. In the laboratory, bark beetles ( Pityogenes chalcographus (Col., Scolytidae)) were reared to produce larvae which were then fed as a food resource to the M. dendrobaena. Eggs of the M. dendrobaena could be placed in newly infested standardized wooden pieces. The time as well as the densities could be varied under constant laboratory conditions. Infested wooden pieces without eggs of M. dendrobaena were used as controls. Only if the eggs of the M. dendrobaena were placed in newly infested wooden pieces up to 48 h, a high mortality of the developing bark beetles could be proven. The mortality of the bark beetles was density dependent. The higher the density of the bark beetles per wooden piece, the more larvae of bark beetles were killed through a larvae of M. dendrobaena per day. In the field similar results were observed. Here, up to 100 M. dendrobaena emerged per m 2 of spruce bark infested with bark beetles. The adults of the M. dendrobaena are present from May up to the first periods of frost on the trunks of trees. Throughout the whole summer, the females of M. dendrobaena are able to lay eggs in newly infested trunks very soon after an infestation of bark beetles. This corresponds well with the results from the laboratory investigations.