The Effect of Floral Strips on the Abundance of Hymenopteran Parasitoids in Apple and Olive Organic Orchards
Abstract: Habitat manipulation techniques improve the availability of resources required by natural enemies to increase their effectiveness. This study focused on the effects of sown floral strips on hymenopteran parasitoid abundance. The experiments were conducted during spring 2007 in one organic low-input apple orchard and five organic olive orchards located in southern France. The density and the diversity of parasitic wasps collected from sown floral strips were higher than those from naturally occurring flora or mowed plants. The family of parasitic waspsof Braconidae was strongly dominant, followed by Mymaridae, Eulophidae and Pteromalidae. Among the 26 studied flowering species in the apple orchard, the greatest diversity and density of parasitic wasps were collected from Potentilla reptans, Achillea millefolium, Trifolium repens and Torilis arvensis. In terms of the early flowering plants, the most important results were observed in Euphorbia helioscopia, Senecio vulgaris and Veronica persica. To give an idea of the functional role of these plants, we studied the parasitic wasps of the diapausing larvae (cocoon) of codling moth Cydia pomonella. We recorded three emerged species: Ascogaster quadridentata, Pristomerus vulnerator and the hyperparasite Perilampus fulvicornis. However, none of these species have been observed on the 26 studied plants. Hence, this result may be suggesting that the studied plants do not have a functional role concerning these parasitoids. These studies may be advantageous for biological control programs in order to select flowering plant species attracting parasitic wasps specific to fruit pests.