Mass releases of Aphidius rhopalosiphi (Hymenoptera: Aphidiinae), and strip management to control of wheat aphids Amandine Levie a , Marie-Anne Legrand a , Pierre Dogot a , Christophe Pels a , Philippe V. Baret b , Thierry Hance a, * a Unite´ d’Ecologie et de Bioge´ographie, Centre de Recherche sur la Biodiversite´, Universite´ catholique de Louvain, Croix du Sud n84,5, 1348 Louvain-la-Neuve, Belgium b Unite´ de ge´ne´tique, Centre de Recherche sur la Biodiversite´, Universite´ catholique de Louvain, Croix-du-Sud 2 box 14, 1348 Louvain-la-Neuve, Belgium Received 13 February 2003; received in revised form 8 June 2004; accepted 28 June 2004 Abstract 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. # 2004 Elsevier B.V. All rights reserved. Keywords: Biological control; Field experiment; Mass release; Strip management; Parasitoid; Aphidius rhopalosiphi; Aphid 1. Introduction Mass releases of control agents are currently used against aphids in greenhouses (Hagvar and Hofsvang, 1991; van Lenteren et al., 1997). In field situations, natural populations of parasitoids can be increased by alternative hosts (Langer and Hance, 2004). According to Stary´ (1970), Cytisus scoparius (L.) (broom) helped the parasitoid Aphidius ervi Haliday in regulating the aphid Acyrthosiphon pisum Harris on alfalfa. The objective of the present study was to test and compare the impact of parasitoid mass-releases and www.elsevier.com/locate/agee Agriculture, Ecosystems and Environment 105 (2005) 17–21 * Corresponding author. Tel.: +32 10 47 34 93; fax: +32 10 47 34 90. E-mail address: Hance@ecol.ucl.ac.be (T. Hance). 0167-8809/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2004.06.004