Studies on the egg parasitism inThaumetopoea pityocampa over a period of four 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 cotton stoppers and stored under laboratory conditions at 20–22°C.Oviposition always started from the base towards the tip of the needles. The emergence of egg parasitoids was observed daily, and the parasitoids were counted and identified.The eggs from which parasitoids emerged were marked for further studies. After removing the adults and opening the eggs, the impact of the species of parasitoids was evaluated by identifying the meconia and other rests (left overs).Ooencyrtus 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 servadeii (Dom.) were collected. The hyperparasitoid Baryscapus transversalis Graham, was found at low densities. Only a few eggs were parasitised by Trichogramma embryophagum Htg. Total mortality of the host eggs varied from 34.7 to 79.7% depending on the period of parasitism and on the numbers of sterile eggs. The impact of the parasitoids was calculated 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 batches. In some cases, a very high percentage (up to 29.2%) of undeveloped eggs was found. In all samples a small percentage of empty eggs was always observed.