Relationships between primary and secondary parasitoids of cereal aphids

Abstract

Abstract: The aim of the study was to compare relationships between primary and secondary parasitoids associated with cereal aphids on winter as well as on spring crops. The study was carried out between 1991–1994 in two regions in Poland, 400 km apart (vicinities of Warsaw and Wrocław). It has been found that in both regions, there occurred three cereal aphid species Sitobion avenae F., Rhopalosiphum padi L. and Metopolophium dirhodum Walk. The groups of parasitic Hymenoptera associated with cereal aphids, and mainly with S. avenae which showed a highest degree of parasitization, were similar in both regions. Although more species of parasitoids were found in the Wrocław region (nine species of primary and 11 species of secondary parasitoids) as compared to the Warsaw region (six and nine, respectively), the species composition was similar in both regions. There were big differences in proportion between primary and secondary parasitoids on spring and winter cereals at both localities. In the case of winter cereals, there were more hyperparasitoids among parasitic Hymenoptera reared from mummified aphids. The primary parasitoids constituted 30% on average while the hyperparasitoids constituted 70%. Aphidius uzbekistanicus Luzh. predominates over other primary parasitoids and Dendrocerus carpenteri Curtis is a dominant species among hyperparasitoids. In the case of spring cereals, the primary/secondary parasitoid ratio is different (primary parasitoids make up to 72% on average, with the secondary parasitoids 28%). Most often, A. uzbekistanicus is a dominating species but in certain years the dominance is not as clear as in winter cereals. The dominance hierarchy within hyperparasitoids is different in different years. The presented results demonstrate that in spite of a great distance between the study areas, the relationships between the cereal aphids' primary and secondary parasitoids show similar trends.