Release of Aphidius rhopalosiphi (Hymenoptera : Aphidiinae) for cereal aphid control: field cage experiments

The potential of the parasitoid Aphidius rhopalosiphi for controlling cerea l aphids was tested in 16 m(2) field cage experiments in 1998 and 1999. In the first year, aphids and parasitoids were released in cages containing na turally occurring populations of aphids and their natural enemies. In the s econd year, aphids and parasitoids were released in cages which had been cl eared of insects by applying insecticide. The growths of the aphid populati ons in the different cages were analysed and compared. In 1998, the release of 50 pairs of parasitoids per cage had no significant effect on aphid pop ulation growth relative to that in the control cages. Even though the aphid population growth rates were less than 60% of that in the control cages, i n the cages in which 100 pairs and 200 pairs of parasitoids were released, it was not possible to show they statistically differed. The aphid populati ons in these three cages were held below 10 aphids per tiller. In 1999, the aphid density was higher and the population grew faster than in 1998. The release of 100 and 200 parasitoids per cage significantly reduced aphid pop ulation growth. A. rhopalosiphi seemed to be a good control agent in field cages, provided they were released at the beginning of aphid population gro wth.