Field investigations were carried out on the parasitism of egg‐batches of T. wilkinsoni Tarns near Lahav, Israel, in 1989. Egg‐batches were collected and studied under laboratory conditions in Hannover. For ovipositions, the host preferred the marginal, especially the southern exposed parts in the forest and in the trees. At Lahav the peak time of egg deposition durated from 13th‐23th of September. The parasitoid impact could be recorded with 38.6%. The most frequent parasitoid was Eutetrastichus servadeii (Dom.), followed by Ooencyrtus pityocampae Mercet. The distribution of the parasitoids in the field was correlated with that of the egg‐batches of the host. O. pityocampae showed a better ability in finding egg‐batches than E. servadeii. O. pityocampae parasitized eggs more frequently at the tip of the batch, whereas E. servadeii parasitized more homogeneously across the egg‐batch. In the laboratory at a temperature of about 19 °C the parasitoids emerged from egg‐batches at the same time as they were expected to emerge in the field in Israel. Among the temperature the age of the host and hyperparasitism are discussed as determining factors for the diapause of O. pityocampae. Zusammenfassung Zur Parasitierung der Eigelege des Pinienprozessionsspinners, Thaumetopoea wilkinsoni Tams (Lep., Thaumetopoeidae) im Lahav‐Gebirge von Israel Im Jahre 1989 erfolgten Freilanduntersuchungen über die Eiparasitoiden des Pinienprozessionsspinners Thaumetopoea wilkinsoni Tams in der Näbe von Lahav (Israsel) sowie anschließend einjährige Beobachtungen der gesammelten Gelege im Labor in Hannover. T. wilkinsoni bevorzugte zur Eiablage südlich exponierte Lagen im Wald und am Baum. Die Hauptablagezeit dauerte 1989 vom 13. bis zum 23. September. Der mittlere Parasitierungsgrad der Eigelege betrug 38,6 %. Das Parasitoidenspektrum bestand im wesentlichen aus Eutetrastichus servadeii (Dom.) und Ooencyrtus pityocampae Mercet. E. servadeii war die häufigere Art. Die Verteilung der Parasitoiden im Gelände ähnelte der der Wirtseigelege. Am Südrand des Waldes waren die höchsten Dichten der Parasitoidenarten anzutreffen. O. pityocampae wies ein besseres Wirtsfindungsvermögen als E. servadeii auf. Innerhalb der Gelege parasitierte O. pityocampae am häufigsten Eier an der Spitze, während E. servadeii zu Beginn der Saison häufiger an der Basis der Gelege auftrat, sich aber mit zunehmender Expositionszeit homogener verteilte. Trotz einer konstanten Labortemperatur von etwa 19 °C schlüpften die Parasitoiden zur gleichen Zeit, zu der sie auch in Israel im Freiland erschienen wären. Für O. pityocampae werden als induzierende Diapausefaktoren, neben der Temperatur, das Alter der Wirtseier sowie Hyperparatisierung diskutiert.

Discrete steps in the process of host selection of Aphidius rosae Haliday (Hym., Braconidae Aphidiinae), a parasitoid of the rose aphid Macrosiphum rosae (L.) (Hem., Aphididae), were studied to assess its specificity in the Australian environment. In a wind tunnel females were strongly attracted only to roses when given a choice between uninfested shoots of hybrid Rosa sp., var. Tea-hybrid and various other plants. The parasitoids were not able to distinguish between infested and uninfested roses when the shoots were 30 cm apart, but they preferred to land on infested plants when shoots were placed only 5 cm apart. These results suggest that aphid-related volatiles involved in host location are detectable by the wasp only over a short distance. Experienced and inexperienced parasitoids were presented with a range of aphid species in choice and no-choice tests. Only the host M . rosae and to a much lesser extent the non-host Macrosiphum euphorbiae (Thomas) were attacked. No larvae of A . rosae were found in M . euphorbiue that were stung when these were dissected. To assess host specificity we argue that more attention should be paid towards the entire host selection process from location of host habitats to location of hosts, host acceptance and host suitability.

Baryscapus servadeii (Domo and Ooencyrtus pityocampae (Mercet) were the most frequent egg parasitoids of Thaumetopoea wilkinsoni Taras (Lep.: Thaumetopoeidae) in the Mountains of Lahav, Israel. Their meconia, remaining in the eggs, differ in structure and can be used to determine the annual rate of parasitism without collecting emergent adults. In B. servadeii, diapausing insects can be discriminated fmm non-diapausing ones by their meconia.

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