Superparasitism by Torymus cyanimus (Hymenoptera: Torymidae in the Volga-Kama region

Abstract

On the basis of a twenty-year investigation, the life-cycle of Torymus cyanimus Boheman (Hymenoptera: Torymidae), a hyperparasitoid of a gall-forming fly in the Volga-Kama region is described. This parasitoid is the top-consumer in a food chain on Cirsium setosum (Willdenow) Iljin, in which the herbivore is Urophora cardui L. (Diptera: Tephritidae) and the primary parasitoids belong to the genus Eurytoma (Hymenoptera: Eurytomidae). Mating and oviposition behaviour were studied, and the superparasitism and larval cannibalism investigated in the second parasitoid generation. The superparasitism in T. cyanimus evolved in connection with the ovipositor elongation, leading to eggs being laid later when the fly host has already been completely consumed by larvae of Eurytoma serratulae F. Hyperparasitism and larval cannibalism in the second generation of T. cyanimus might account for the evolution of hyperparasitism in this species.