Seasonal history ofMacrocentrus grandii [Hym.: Braconidae] andEriborus terebrans [Hym.: Ichneumonidae], two parasitoids of the European corn borer,Ostrinia nubilalis [Lep.: Pyralidae]

The seasonal histories and phenological relationships of European corn borer,Ostrinia nubilalis (Hübner), and its 2 parasitoids,Macrocentrus grandii (Goidanich) andEriborus terebrans (Gravenhorst) were studied in southcentral Minnesota. Both parasitoids overwintered in mature borer larvae, broke diapause, completed development, and emerged at the same time as did borer adults. Thus the 1st generation parasitoids coincided with the peak abundance of their preferred larval instars of the 1st host generation. Both parasitoids had a 2nd generation, matching the bivoltinism ofO. nubilatis in Minnesota. The activity of 2nd generationE. terebrans was before the peak 2nd generation borer moth flight and was not synchronized with the peak abundance of 2nd generation borer larvae. The peak activity of 2nd generationM. grandii occurred after the peak 2nd generation borer moth flight and was fully synchronized with the peak abundance of 2nd generation borer larvae. Thus,M. grandii has both generations synchronized with the host seasonal history, and was the more effective of the 2 parasitoids.