THE IMPACT OF MEDETERA-DENDROBAENA KOWARZ (DIPT, DOLICHOPODIDAE) ON BARK BEETLES

Many natural enemies of bark beetles have been studied in central Euro pe. However, little is known about the impact that these natural enemi es might have on developing bark beetle populations in the field. The larvae of Medetera dendrobaena are known to be important natural preda tors of bark beetles, especially in virgin forests. In the laboratory, bark beetles (Pityogenes chalcographus (Col., Scolytidae)) were reare d to produce larvae which were then fed as a food resource to the M. d endrobaena. Eggs of the M. dendrobaena could be placed in newly infest ed standardized wooden pieces. The time as well as the densities could be varied under constant laboratory conditions. Infested wooden piece s without eggs of M. dendrobaena were used as controls. Only if the eg gs of the M. dendrobaena were placed in newly infested wooden pieces u p to 48 h, a high mortality of the developing bark beetles could be pr oven. The mortality of the bark beetles was density dependent. The hig her 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. dendr obaena 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 per iods of frost on the trunks of trees. Throughout the whole summer, the females of M. dendrobaena are able to lay eggs in newly infested trun ks very soon after an infestation of bark beetles. This corresponds we ll with the results from the laboratory investigations.