STUDIES ON THE EGG PARASITISM IN THAUMETOPOEA-PITYOCAMPA OVER A PERIOD OF 4 YEARS (1991-1994) AT MARIKOSTINO BULGARIA/

In Bulgaria near Marikostino, in a forest of Pinus nigra Arn. 239 egg batches were sampled over four generations of Thaumetopoea pityocampa (Den. & Schiff.) (Lep., Thaumetopoeidae) in various seasons. Directly after collection the batches were singled in test tubes, closed with c otton stoppers and stored under laboratory conditions at 20-22 degrees C. Oviposition always started from the base towards the tip of the ne edles. The emergence of egg parasitoids was observed daily, and the pa rasitoids were counted and identified. The eggs from which parasitoids emerged were marked for further studies. After removing the adults an d opening the eggs, the impact of the species of parasitoids was evalu ated by identifying the meconia and other rests (left overs). Ooencyrt us pityocampae (Mercet) was the most abundant egg parasitoid, followed by Anastatus bifasciatus (Fonsc.). Only few individuals of Baryscapus servadeii (Dom.) were collected. The hyperparasitoid Baryscapus trans versalis Graham, was found at low densities. Only a few eggs were para sitised by Trichogramma embryophagum Htg. Total mortality of the host eggs varied from 34.7 to 79.7% depending on the period of parasitism a nd on the numbers of sterile eggs. The impact of the parasitoids was c alculated to be 9.3-38.9%, depending on the period when parasitism had taken place. The mean number of eggs per batch varied from 203 to 253 . The rate of parasitism was reduced by early sampling of the egg batc hes. In some cases, a very high percentage (up to 29.2%) of undevelope d eggs was found. In all samples a small percentage of empty eggs was always observed.