Mass releases of Aphidius rhopalosiphi (Hymenoptera: Aphidiinae), and strip management to control of wheat aphids

Biological control of cereal aphids was attempted during two years, using two approaches: (1) mass-release of Aphidius rhopalosiphi (21,000 individuals/ha) in May and (2) use of a clover-ryegrass strip as a parasitoid reservoir. Two aphid species (Metopolophium festucae and Acyrtosiphon pisum) considered as alternative hosts for cereal aphid parasitoids occurred in the grassy strips. Three fields for each of the mass release or strip management were compared in 2000 with two control fields where no aphid control was done. Aphid population growth was significantly reduced under both mass release and management compared to controls. There was no significant difference between the two treatments. Yet, the parasitism rates were significantly higher under mass release and strip management than in the controls. In 2001, three fields per treatment were compared with three controls. Aphid numbers were very low in all fields, strip management being the only treatment to slow down aphid population growth.