Structure of egg‐batches of Thaumetopoea pityocampa (Den. and Schiff.) (Lep., Thaumetopoeidae), egg parasitoids and rate of egg parasitism on the Iberian Peninsula

Abstract

In four regions of the Iberian Peninsula 273 egg‐batches of the pine processionary moth were collected after hatching of the caterpillars in 1991 and 1992. After collection, the batches were stored singly in test tubes closed with foam stoppers under laboratory conditions at 20–25°C. The number of eggs in each egg‐batch varied between 37 and 312 and the length of the batches between 0.6 and 4.2 cm. Independently of the pine species infested, seven to nine rows of eggs were counted, wrapped around one pair of needles. A correlation was found between number of eggs and the product of number of egg rows and length of egg‐batches (82% < r2 < 97%). Oviposition almost always started from the base towards the tip of the needles. The egg parasitoids that emerged were counted daily, removed and identified. Later in the year of oviposition, after the end of the period of emergence of the parasitoids, the scale cover of the egg‐batches were removed. One year later, all eggs were opened and the contents, such as parasitoid meconia and remains of caterpillars, were determined. The hatching rate of the caterpillars varied from 47.2 to 79.7%. The rate of parasitism fluctuated between 11.3 and 31.7%, but 44% of parasitoids died before successful emergence. Four species of Chalcidoidea were identified: Baryscapus servadeii (Dom.), Ooencyrtus pityocampae (Mercet), Anastatus bifasciatus (Fonsc.) and Trichogramma sp. Baryscapus servadeii and O. pityocampae were the most abundant species, followed by Trichogramma sp. Baryscapus servadeii emerged mainly in June and O. pityocampae in April or June, depending on the region. For A. bifasciatus only males, and for B. servadeii females emerged except one male. In O. pityocampae, a relatively high percentage of males (5.4–10.4%) was found.