Egg Batches Parasitism of Processionary Moth Thaumetopoea pityocampa (Lepidoptera, Thaumetopoeidae) from Two Atlas Cedar Ecotypes in Algeria

Abstract

In the Atlas cedar forests located on the northern massifs of the Blidean Atlas and at the eastern extension of the Saharan Atlas, 79 egg batches of processionary moth Thaumetopoea pityocampa (Denis & Schiffermuller, 1775) were collected during the summer period from two sites: Chrea National park (46), and Ouled Yagoub forest (33). To assess the effect of the egg batches characteristics on the parasitism, the eggs were monitored after the hatching of the larvae and/or the emergence of the parasitoids. The average number of eggs/batches in the Ouled Yagoub site (184 eggs) was significantly higher than of the population of Chrea (151). Data analysis showed that the means comparisons of the hatched and unhatched number of eggs between the two sites were significant. In the case of the population of Chrea, the egg mass was laid in the form of a cylinder on twigs of relatively small diameters while for the population of Ouled Yagoub eggs were laid in the form of plates on twigs of larger diameter, thus more exposed to parasitoids. For the two populations, three active egg parasitoids were identified: Ooencyrtus pityocampae (Mercet, 1921) (Encyrtidae), Baryscapus servadeii (Domenichini,1965) (Eulophidae), and Trichogramma embryophagum (Hartig, 1838) (Trichogrammatidae), the most dominant. These parasitoids were heterogeneously distributed on the egg batches collected in the cedar’s plantation of the Chrea, but homogeneously on the egg batches collected in the Ouled Yagoub cedar forest. The activity and distribution of parasitoids on the egg-laying surface are influenced by the form on the branch chosen by the female.